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Item 8. Financial Statements and Supplementary Data

2024-02-16 compared with 2023-02-24 · 357 added, 370 removed, 1817 unchanged (29% of the section changed)

FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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The communication of critical audit matters does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Regulatory Assets and Regulatory Liabilities - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Regulatory Accounting - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Critical Audit Matter Description

Alliant Energy Corporation, through its wholly-owned subsidiaries Interstate Power and Light Company and Wisconsin Power and Light Company, is subject to rate regulation by the Federal Energy Regulatory Commission and the respective state commissions in Iowa and Wisconsin (collectively the “regulatory agencies”).

Alliant Energy Corporation, through its wholly-owned subsidiaries Interstate Power and Light Company and Wisconsin Power and Light Company, is subject to rate regulation by regulatory agencies.

Management has determined it meets the requirements under accounting principles generally accepted in the United States of America to prepare its financial statements applying the Regulated Operations Topic 980 of the Financial Accounting Standards Board’s Accounting Standards Codification.

As of December 31, 2022, the Company had a recorded consolidated regulatory assets balance of $ 2,046 million and regulatory liabilities balance of $ 1,324 million.

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The Company’s rates are subject to regulatory rate-setting processes and periodic earnings oversight.

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The Company’s regulatory assets and regulatory liabilities are recognized in accordance with the rulings of the regulatory agencies.

A change in these rulings may result in a material impact on results of operations and the amount of assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of the regulatory assets and regulatory liabilities.

We identified the impact of rate regulation as a critical audit matter due to the significant judgments made by management to support its assertions about impacted account balances and disclosures and the high degree of subjectivity involved in assessing the impact of future regulatory orders on the financial statements.

A change in these rulings may result in a material impact on results of operations and the amount of certain assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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We identified the impact of rate regulation as a critical audit matter due to the significant judgments made by management to support its assertions about certain impacted account balances and disclosures and the high degree of subjectivity involved in assessing the impact of relevant future regulatory orders on the financial statements.

Management judgments include assessing the likelihood of the recovery of incurred costs and refund of obligations to customers in future rates.

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Our audit procedures related to the regulatory filings by management and the uncertainty of future decisions by the regulatory agencies included the following, among others:

• We tested the effectiveness of management’s controls over the evaluation of the likelihood of recovery in future customer rates for regulatory assets and the likelihood of a probable refund to customers or reduction in future customer rates for regulatory liabilities;

and the monitoring and evaluation of regulatory developments that may affect the likelihood of recovering costs in future rates or of a future reduction in rates.

• We obtained the Company’s analysis supporting the probability of recovery for regulatory assets or refund to customers or future reduction in customer rates for regulatory liabilities not yet addressed in a regulatory order to assess management’s assertion that amounts are probable of recovery in future customer rates or represent a probable refund to customers or reduction in future customer rates.

• We inquired of management regarding current events impacting the Company and inspected minutes of the board of directors and other committees of the Company and evaluated whether matters were identified that may have an impact on recorded regulatory asset and liability balances.

• We read relevant regulatory orders issued by the regulatory agencies for the Company and other relevant public utilities, regulatory statutes, interpretations, procedural memorandums, filings made by certain stakeholders, and other publicly available information to assess the likelihood of recovery in future customer rates based on precedents of the regulatory agencies’ treatment of similar costs under similar circumstances.

We evaluated the external information and whether there were matters in such information that would be contradictory to the assessment of recovery of the Company’s regulatory assets or refund of regulatory liabilities.

• We inquired of management about property, plant, and equipment, net that may be abandoned.

We inspected minutes of the board of directors and other committees of the Company, regulatory orders and other filings with the regulatory agencies to identify evidence that may contradict management’s assertion regarding probability of an abandonment or that may have an impact on the recorded balances.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including the regulatory balances recorded.

• We tested the effectiveness of management’s controls over the evaluation of certain regulatory assets and regulatory liabilities, including the monitoring and evaluation of regulatory developments that may affect the likelihood of recovering costs in future rates or of a future reduction in rates.

• We inspected and evaluated the Company’s analysis supporting the probability of recovery for certain regulatory assets or refund to customers or future reduction in customer rates for regulatory liabilities not yet addressed in a regulatory order to assess management’s assertions.

• We read relevant regulatory orders, interpretations, filings made by the Company or its stakeholders, and other publicly available information issued by the regulatory agencies that pertain to the Company.

We evaluated the external information and assessed whether there are matters in such information that would be contradictory to management’s assertion of probability of recovery of certain regulatory assets or refund of regulatory liabilities.

• We inspected minutes of the board of directors and other committees of the Company, regulatory orders and other filings with the regulatory agencies to identify evidence that may contradict management’s assertion regarding probability of abandonment or that may have an impact on the recorded balances.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

/s/ DELOITTE & TOUCHE LLP

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We have served as the Company’s auditor since 2002.

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ALLIANT ENERGY CORPORATION

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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Retained earnings 3,756 3,509

Accumulated other comprehensive income 1 —

Shares in deferred compensation trust - 379,006 and 402,134 shares at a weighted average cost of $ 34.48 and $ 32.63 per share

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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Deferred tax expense (benefit) and tax credits 14 13 ( 78 )

Equity component of allowance for funds used during construction ( 74 ) ( 44 ) ( 18 )

Other 35 27 35

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Accounts receivable ( 414 ) ( 672 ) ( 530 )

Materials and supplies ( 62 ) ( 27 ) ( 13 )

Regulatory assets 24 ( 108 ) 51

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Derivative liabilities 19 70 ( 17 )

Deferred income taxes 4 193 171

Deferred income taxes (a) 84 4 193

Pension and other benefit obligations ( 28 ) ( 97 ) ( 137 )

DAEC PPA amendment buyout payment — — ( 110 )

Other 12 ( 76 ) ( 64 )

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Cash receipts on sold receivables 453 598 502

Proceeds from sales of partial ownership interests in West Riverside 120 — —

Other ( 120 ) ( 47 ) ( 61 )

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Net change in commercial paper ( 167 ) 127 126

Contributions from noncontrolling interest 29 — —

Distributions to noncontrolling interest ( 29 ) — —

Other 3 2 ( 13 )

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Interest ($ 378 ) ($ 311 ) ($ 272 )

Income taxes, net ($ 6 ) ($ 3 ) $ 5

Income taxes, net (a)

$ 88 ($ 6 ) ($ 3 )

Significant non-cash investing and financing activities:

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Beneficial interest obtained in exchange for securitized accounts receivable $ 216 $ 185 $ 214

(a) 2023 includes $ 98 million of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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Additional Other Deferred Preferred

Common Paid-In Retained Comprehensive Compensation Stock Noncontrolling Total

Stock Capital Earnings Income (Loss) Trust of IPL Interest Equity

Common Paid-In Retained Comprehensive Compensation Stock Total

Stock Capital Earnings Income (Loss) Trust of IPL Equity

(in millions)

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( 403 ) ( 403 )

Equity forward settlements and Shareowner Direct Plan issuances 247 247

Shareowner Direct Plan issuances 1 27 28

Equity-based compensation plans and other 18 ( 1 ) 17

Adoption of new accounting standard, net of tax (refer to Note 1( l ) )

Other comprehensive loss, net of tax ( 2 ) ( 2 )

Redemption of IPL’s cumulative preferred stock ( 200 ) ( 200 )

Other comprehensive income, net of tax 1 1

Ending balance 3 2,749 3,250 — ( 12 ) — 5,990

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Equity-based compensation plans and other 3 1 ( 1 ) 3

Redemption of IPL’s cumulative preferred stock ( 200 ) ( 200 )

Other comprehensive income, net of tax 1 1

Ending balance 3 2,777 3,509 — ( 13 ) — 6,276

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( 456 ) ( 456 )

Shareowner Direct Plan issuances 25 25

At-the-market offering program, net and Shareowner Direct Plan issuances 246 246

Equity-based compensation plans and other 7 7

Contributions from noncontrolling interest 29 29

Distributions to noncontrolling interest ( 29 ) ( 29 )

Other comprehensive income, net of tax 1 1

Ending balance $ 3 $ 3,030 $ 3,756 $ 1 ($ 13 ) $ — $ 6,777

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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Regulatory Assets and Regulatory Liabilities - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Regulatory Accounting - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Critical Audit Matter Description

Interstate Power and Light Company is subject to rate regulation by the Federal Energy Regulatory Commission and state commission in Iowa (collectively the “regulatory agencies”).

Interstate Power and Light Company is subject to rate regulation by regulatory agencies.

As of December 31, 2022, the Company had a recorded consolidated regulatory assets balance of $ 1,386 million and regulatory liabilities balance of $ 754 million.

The Company’s rates are subject to regulatory rate-setting processes and periodic earnings oversight.

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The Company’s regulatory assets and regulatory liabilities are recognized in accordance with the rulings of the regulatory agencies.

A change in these rulings may result in a material impact on results of operations and the amount of assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of the regulatory assets and regulatory liabilities.

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A change in these rulings may result in a material impact on results of operations and the amount of certain assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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Management judgments include assessing the likelihood of the recovery of incurred costs and refund of obligations to customers in future rates.

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Our audit procedures related to the regulatory filings by management and the uncertainty of future decisions by the regulatory agencies included the following, among others:

and the monitoring and evaluation of regulatory developments that may affect the likelihood of recovering costs in future rates or of a future reduction in rates.

• We inquired of management about property, plant, and equipment, net that may be abandoned.

We inspected minutes of the board of directors and other committees of the Company, regulatory orders, and other filings with the regulatory agencies to identify evidence that may contradict management’s assertion regarding probability of an abandonment or that may have an impact on the recorded balances.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including the regulatory balances recorded.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

/s/ DELOITTE & TOUCHE LLP

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We have served as the Company’s auditor since 2002.

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INTERSTATE POWER AND LIGHT COMPANY

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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Current liabilities:

Current maturities of long-term debt $ 500 $ —

Accounts payable 262 239

Accounts payable to associated companies 28 39

Accrued taxes 50 52

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Regulatory liabilities 72 114

Other 101 141

Total current liabilities 1,025 581

Long-term debt, net 3,646 3,643

Long-term debt, net (excluding current portion) 3,445 3,646

Other liabilities:

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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(in millions)

Cash flows from (used for) operating activities:

Cash flows from operating activities:

Net income $ 366 $ 360 $ 365

Adjustments to reconcile net income to net cash flows from (used for) operating activities:

Adjustments to reconcile net income to net cash flows from operating activities:

Depreciation and amortization 388 381 375

Deferred tax benefit and tax credits ( 13 ) ( 14 ) ( 52 )

Equity component of allowance for funds used during construction ( 8 ) ( 7 ) ( 17 )

Other ( 2 ) ( 21 ) ( 10 )

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Accounts receivable ( 437 ) ( 611 ) ( 539 )

Materials and supplies ( 39 ) ( 13 ) ( 7 )

Regulatory assets 58 56 30

Derivative assets 84 ( 54 ) ( 55 )

Gas stored underground, at weighted average cost ( 20 ) ( 20 ) 2

Accounts payable ( 68 ) 65 15

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Derivative liabilities ( 16 ) 42 ( 8 )

Deferred income taxes ( 24 ) 62 79

Deferred income taxes (a) 36 ( 24 ) 62

Pension and other benefit obligations ( 11 ) ( 65 ) ( 59 )

DAEC PPA amendment buyout payment — — ( 110 )

Other ( 6 ) ( 86 ) ( 17 )

Net cash flows from (used for) operating activities 83 153 ( 6 )

Net cash flows from operating activities 261 83 153

Cash flows from (used for) investing activities:

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Proceeds from issuance of long-term debt 296 — 300

Payments to retire long-term debt — — ( 200 )

Other 7 4 ( 10 )

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Interest ($ 150 ) ($ 148 ) ($ 138 )

Income taxes, net $ 36 $ 47 ($ 18 )

Income taxes, net (a)

$ 117 $ 36 $ 47

Significant non-cash investing and financing activities:

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Beneficial interest obtained in exchange for securitized accounts receivable $ 216 $ 185 $ 214

(a) 2023 includes $ 76 million of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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INTERSTATE POWER AND LIGHT COMPANY

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Capital contributions from parent 50 50

Redemption of cumulative preferred stock ( 200 ) ( 200 )

Ending balance 33 2,807 929 — 3,769

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Common stock dividends ( 321 ) ( 321 )

Capital contributions from parent 50 50

Redemption of cumulative preferred stock ( 200 ) ( 200 )

Ending balance 33 2,807 968 — 3,808

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Common stock dividends ( 280 ) ( 280 )

Capital contributions from parent 80 80

Ending balance $ 33 $ 2,887 $ 1,054 $ — $ 3,974

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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Regulatory Assets and Regulatory Liabilities - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Regulatory Accounting - Impact of rate regulation on the financial statements - Refer to Notes 1, 2, and 3 to the financial statements

Critical Audit Matter Description

Wisconsin Power and Light Company is subject to rate regulation by the Federal Energy Regulatory Commission and state commission in Wisconsin (collectively the “regulatory agencies”).

Wisconsin Power and Light Company is subject to rate regulation by regulatory agencies.

As of December 31, 2022, the Company had a recorded consolidated regulatory assets balance of $ 660 million and regulatory liabilities balance of $ 570 million.

The Company’s rates are subject to regulatory rate-setting processes and periodic earnings oversight.

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The Company’s regulatory assets and regulatory liabilities are recognized in accordance with the rulings of the regulatory agencies.

A change in these rulings may result in a material impact on results of operations and the amount of assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of the regulatory assets and regulatory liabilities.

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A change in these rulings may result in a material impact on results of operations and the amount of certain assets and liabilities in the financial statements.

Future regulatory rulings may impact the carrying value and accounting treatment of certain regulatory assets and regulatory liabilities.

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Management judgments include assessing the likelihood of the recovery of incurred costs and refund of obligations to customers in future rates.

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Our audit procedures related to the regulatory filings by management and the uncertainty of future decisions by the regulatory agencies included the following, among others:

and the monitoring and evaluation of regulatory developments that may affect the likelihood of recovering costs in future rates or of a future reduction in rates.

• We inquired of management about property, plant, and equipment, net that may be abandoned.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including the regulatory balances recorded.

• We evaluated the Company’s disclosures related to the impacts of rate regulation and regulatory developments, including disclosures related to certain regulatory balances recorded.

/s/ DELOITTE & TOUCHE LLP

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We have served as the Company’s auditor since 2002.

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WISCONSIN POWER AND LIGHT COMPANY

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

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Current liabilities:

Current maturities of long-term debt $ — $ 250

Commercial paper $ 318 $ 290

Accounts payable 293 456

Accrued interest 40 38

Regulatory liabilities 35 92

Other 111 112

Total current liabilities 775 949

Long-term debt, net (excluding current portion) 2,770 2,179

Long-term debt, net 3,070 2,770

Other liabilities:

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Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

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Deferred tax expense (benefit) and tax credits ( 13 ) 4 ( 79 )

Equity component of allowance for funds used during construction ( 59 ) ( 36 ) ( 11 )

Other 25 21 22

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Derivative assets 65 ( 7 ) ( 87 )

Accounts payable ( 57 ) 22 4

Regulatory liabilities ( 57 ) ( 31 ) ( 67 )

Deferred income taxes 32 132 90

Deferred income taxes (a) 50 32 132

Pension and other benefit obligations ( 19 ) ( 19 ) ( 63 )

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Construction and acquisition expenditures ( 1,019 ) ( 1,020 ) ( 686 )

Proceeds from sales of partial ownership interests in West Riverside 120 — —

Other ( 47 ) ( 13 ) ( 30 )

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Net change in commercial paper 28 54 ( 21 )

Contributions from noncontrolling interest 29 — —

Distributions to noncontrolling interest ( 29 ) — —

Other ( 16 ) ( 9 ) ( 12 )

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Supplemental cash flows information:

Cash (paid) refunded during the period for:

Cash paid during the period for:

Interest ($ 146 ) ($ 111 ) ($ 101 )

Income taxes, net ($ 56 ) ($ 38 ) $ 13

Income taxes, net (a)

($ 50 ) ($ 56 ) ($ 38 )

Significant non-cash investing and financing activities:

Accrued capital expenditures $ 217 $ 319 $ 81

(a) 2023 includes $ 22 million of proceeds from renewable tax credits transferred to other corporate taxpayers

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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WISCONSIN POWER AND LIGHT COMPANY

CONSOLIDATED STATEMENTS OF EQUITY

Total WPL Common Equity

Common Paid-In Retained Noncontrolling Total

Stock Capital Earnings Interest Equity

Common Paid-In Retained Total

Stock Capital Earnings Equity

(in millions)

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Capital contributions from parent 530 530

Other ( 1 ) ( 1 )

Ending balance 66 2,233 1,192 3,491

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Capital contributions from parent 245 245

Contributions from noncontrolling interest 29 29

Distributions to noncontrolling interest ( 29 ) ( 29 )

Other ( 1 ) ( 1 )

Ending balance $ 66 $ 2,478 $ 1,353 $ 3,897

Refer to accompanying Combined Notes to Consolidated Financial Statements.

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ALLIANT ENERGY CORPORATION

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freight brokerage services;

wind turbine blade recycling services;

and a rail-served warehouse in Iowa.

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The non-utility wind farm includes a 50 % cash equity ownership interest in a 225 MW wind farm located in Oklahoma.

The Sheboygan Falls Energy Facility is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is leased to WPL for an initial period of 20 years ending in 2025.

The Sheboygan Falls Energy Facility is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is currently leased to WPL through 2039.

Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries.

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Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.

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NOTE 1 (c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements.

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As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Federal Tax Reform repealed corporate federal alternative minimum tax and allowed unutilized alternative minimum tax credits to be refunded over four tax years beginning with the U.S.

federal tax return for calendar year 2018.

Pursuant to the Coronavirus Aid, Relief, and Economic Security Act, Alliant Energy received the remaining alternative minimum tax credits refunds in 2020.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries.

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Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return.

IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities.

IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities.

IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).

The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2022, 2021 and 2020.

The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers.

In 2023, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery storage facilities to other corporate taxpayers in exchange for cash.

Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes.

For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price.

Renewable tax credits and any related valuation allowances are derecognized when control of the tax credits is transferred to other corporate taxpayers.

A majority of the differences between actual renewable tax credits and renewable tax credits used to determine rates are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

The cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities.

Refer to Notes 12 and 17(d) for further discussion of the transfer of renewable tax credits to other corporate taxpayers, including related valuation allowances and indemnification requirements, respectively.

NOTE 1 (d) Cash, Cash Equivalents and Restricted Cash - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days.

At December 31, 2023, Alliant Energy’s and IPL’s cash and cash equivalents included $ 45 million of money market fund investments, with a weighted average interest rate of 5 %.

At December 31, 2023 and 2022, Alliant Energy’s restricted cash related to requirements in Sheboygan Power, LLC’s debt agreement.

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Utility Plant -

General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation.

Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense.

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These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions.

Depreciation expense is included within the recoverable cost of service component of rates collected from customers.

Depreciation expense is included within the recoverable cost of service

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component of rates collected from customers.

The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:

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2023 2022 2021 2023 2022 2021

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Other 6.2 % 6.1 % 6.1 % 4.6 % 4.9 % 5.4 %

In December 2021, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2023 as a result of a recently completed depreciation study.

WPL estimates the new average rates of depreciation for its electric generation, electric distribution and gas properties will be approximately 3.6 %, 2.7 % and 2.9 %, respectively, during 2023.

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting.

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The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered.

The unbilled component is estimated and recorded at the end of each reporting period based on estimated amounts of energy delivered to customers since the end of each customer’s last billing period.

The unbilled component is based on estimates of daily system demand volumes, customer usage by class, temperature impacts, line losses and the most recent customer rates.

The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period.

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The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

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Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

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Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for:

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Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity.

Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements.

Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are primarily recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements.

The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

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WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings.

Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s

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income statements.

An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

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Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

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Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements.

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The cumulative effects of the under-/over-collection of these costs for IPL are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

NOTE 1 (h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs.

The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets.

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Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.

Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on derivative instruments.

Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on commodity derivative instruments.

Refer to Notes 15 , 16 and 17(f) for further discussion of derivatives and related credit risk.

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If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.

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NOTE 1 (j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs.

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The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset.

Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets.

Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated

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operations are recorded to regulatory assets on the balance sheets.

Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets.

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The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments.

The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, significant weather related matters including the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs.

The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs.

The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.

In 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures.

Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020.

IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $ 12 million (after-tax $ 9 million) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 17(d) for further discussion).

This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s equity statement for 2020.

NOTE 1 (m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics:

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The financial statements do not reflect any consolidation of VIEs.

In 2022, WPL 2022 Solar Holdco, LLC was formed as a joint venture to own and operate project companies responsible for the construction, ownership and operation of various solar generation assets.

Members of the joint venture were a WPL subsidiary (the managing member) and a tax equity partner.

In the second quarter of 2022, the WPL subsidiary and the tax equity partner contributed $ 62 million and $ 29 million, respectively, to WPL 2022 Solar Holdco, LLC in exchange for membership interests, and $ 88 million of the contributed funds were paid to WPL in exchange for equity interests in the project companies.

The tax equity partner's contributions were represented as a noncontrolling interest within total equity on Alliant Energy’s and WPL’s balance sheets as of June 30, 2022.

In the second quarter of 2022, Alliant Energy and WPL consolidated this joint venture as it was a VIE in which WPL held a variable interest, and WPL controlled decisions that were significant to the joint venture’s ongoing operations and economic results (i.e., WPL was the primary beneficiary).

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In August 2022, the Inflation Reduction Act of 2022 was enacted.

Following its enactment, WPL evaluated the provisions of the new legislation and determined that retaining full ownership of the solar projects is expected to result in more cost benefits for its customers.

As a result, in the third quarter of 2022, WPL and the tax equity partner terminated the tax equity partnership, and WPL returned the $ 29 million of initial funding to the tax equity partner, resulting in the reversal of the noncontrolling interest within total equity on Alliant Energy’s and WPL’s balance sheets as of December 31, 2022.

Alliant Energy and WPL no longer expect their solar generation project construction costs to be financed with capital from tax equity partners, which would result in higher rate base amounts compared to those previously approved by the PSCW for WPL’s planned approximately 1,100 MW of solar generation.

Alliant Energy and WPL concluded that no disallowance of anticipated higher rate base amounts was required as of December 31, 2022 given full ownership of WPL's planned solar generation is expected to result in more cost benefits for WPL's customers.

NOTE 1 (n) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement.

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At December 31, regulatory assets were comprised of the following items (in millions):

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Alliant Energy IPL WPL

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Pension and OPEB costs 347 392 171 197 176 195

Commodity cost recovery 160 42 1 2 159 40

Assets retired early 273 70 259 53 14 17

AROs 194 151 160 110 34 41

Commodity cost recovery 120 160 12 1 108 159

Derivatives 102 84 34 48 68 36

Assets retired early 70 92 53 66 17 26

IPL’s DAEC PPA amendment 66 90 66 90 — —

WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48

IPL’s DAEC PPA amendment 42 66 42 66 — —

Other 205 146 68 63 137 83

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IPL’s regulatory assets that were not earning a return consisted primarily of retired analog electric meters, emission allowances and costs for certain construction projects.

WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the wholesale portion of under-collected costs, and costs for future expansion projects.

WPL’s regulatory assets that were not earning a return consisted primarily of costs for certain construction projects.

The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost.

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Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates.

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Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s retail and wholesale customers, which are based upon pension and OPEB costs determined in accordance with GAAP and are calculated in accordance with IPL’s and WPL’s respective regulatory jurisdictions.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms.

The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding.

In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 37 million deferral as of December 31, 2022, which will be collected in 2023 from its retail electric customers, plus interest.

In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 117 million deferral as of December 31, 2022, which is currently expected to be addressed in WPL’s next retail electric rate review.

AROs - Alliant Energy, IPL and WPL believe it is probable that certain differences between expenses accrued for AROs related to their utility operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets.

Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized.

Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Refer to Note 15 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2022, which result in comparable changes to regulatory assets/liabilities on the balance sheets.

Assets retired early - IPL and WPL have retired various natural gas- and coal-fired EGUs, and IPL has retired certain analog electric meters.

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Recovery Regulatory Approval

IPL Lansing 2023 $ 216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a)

IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC

IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC

Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC

IPL Analog electric meters 2019 24 Return of remaining net book value through 2028 IUB and FERC

WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $ 110 million in exchange for shortening the term of its DAEC PPA by 5 years.

The payment was included in “DAEC PPA amendment buyout payment” in Alliant Energy’s and IPL’s cash flows used for operating activities in 2020.

The buyout payment, including a return on, will be recovered from IPL’s retail and wholesale customers from 2021 through the end of 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

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(a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.

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In 2023, in conjunction with IPL's retirement of the Lansing Generating Station, IPL reclassified the remaining net book value of the associated AROs from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms.

In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 37 million deferral as of December 31, 2022, which was collected in 2023 from its retail electric customers, plus interest.

In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 117 million deferral as of December 31, 2022, which WPL is collecting from October 2023 through December 2025 from its retail electric customers, plus interest ($ 12 million was collected in 2023).

In 2023, actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $ 34 million regulatory liability as of December 31, 2023, which is expected to be addressed in a future regulatory proceeding.

Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Refer to Note 15 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2023, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project.

Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040.

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $ 110 million in exchange for shortening the term of its DAEC PPA by 5 years.

The buyout payment, including a return on, is being recovered from IPL’s retail and wholesale customers from 2021 through the end of 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):

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WPL’s West Riverside liquidated damages 1 32 — — 1 32

Electric transmission cost recovery 20 51 10 27 10 24

Other 84 65 56 39 28 26

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A significant portion of the remaining regulatory liabilities is not used to adjust revenue requirement calculations.

Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform.

The majority of these benefits related to accelerated depreciation are subject to tax normalization rules.

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WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in 2020.

A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities.

In 2020, the PSCW authorized WPL to record the liquidated damages as a regulatory liability, which the PSCW authorized to be returned to WPL’s retail customers in 2022 and 2023, resulting in decreases in regulatory liabilities on Alliant Energy’s and WPL’s balance sheets and decreases in depreciation and amortization expenses in Alliant Energy’s and WPL’s income statements in 2022.

Electric transmission cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s electric transmission cost recovery mechanisms.

In 2020, pursuant to an IUB order, IPL issued $ 42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements in 2020.

Derecho Windstorm - In August 2020, a derecho windstorm caused considerable damage to IPL’s electric distribution system in its service territory, and over 250,000 of its customers lost power.

IPL completed its initial restoration and rebuilding efforts in August 2020.

As of December 31, 2022, approximately $ 140 million of costs from the windstorm were recorded substantially to “Property, plant and equipment, net” on Alliant Energy’s and IPL’s balance sheets.

In December 2020, IPL received approval from the IUB for utilization of a regulatory account to track certain incremental costs and benefits incurred resulting from the windstorm.

These incremental costs and benefits were not addressed in the IUB’s order for IPL’s 2020 forward-looking Test Period electric subsequent proceeding, and are expected to be addressed in future regulatory proceedings.

Tax benefits and the incremental operation and maintenance expenses resulting from the windstorm were deferred and recorded as a net regulatory liability of $ 8 million as of December 31, 2022, which is included in “Other” regulatory liabilities in the above table.

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A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for

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payment, which were non-cash investing activities.

Pursuant to PSCW authorization, WPL’s amortization of liquidated damages related to West Riverside construction procurement contracts was used to offset increases in WPL’s retail electric 2022/2023 Test Period revenue requirement, resulting in decreases in regulatory liabilities on Alliant Energy’s and WPL’s balance sheets and decreases in depreciation and amortization expenses in Alliant Energy’s and WPL’s income statements in 2023.

Rate Reviews -

IPL’s Retail Electric Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers based on a 2020 forward-looking Test Period.

The key drivers for IPL’s request included recovery of capital projects, including new wind generation.

IPL concurrently filed for interim retail electric rates based on 2018 historical data as adjusted for certain known and measurable changes occurring in the first quarter of 2019.

An interim retail electric base rate increase of $ 90 million, on an annual basis, was implemented effective April 1, 2019.

In October 2019, IPL reached a settlement agreement with certain stakeholders for an annual retail electric base rate increase of $ 127 million.

In January 2020, the IUB issued an order approving the settlement with final rates, which were effective February 26, 2020.

The agreement includes both the recovery of and a return on IPL’s early retired EGUs, and the recovery of IPL’s retired analog electric meters.

In addition, as discussed in Note 1(g) , the net impact of certain costs and benefits resulting from IPL’s 1,000 MW expansion of wind generation in 2019 and 2020 is being recovered from its retail electric customers through the renewable energy rider.

The agreement also includes IPL providing retail electric billing credits, which began in the third quarter of 2020 through June 2021, and in aggregate include $ 27 million of excess deferred tax benefits and $ 8 million from a partial refund of interim rates implemented in 2019.

In 2021, the IUB issued an order for IPL’s 2020 forward-looking Test Period electric subsequent proceeding, which compared actual revenues and costs to those initially forecasted by IPL, and authorized IPL to maintain its current retail electric rates.

IPL’s Retail Gas Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers based on a 2020 forward-looking Test Period.

In October 2019, IPL reached a settlement agreement with certain stakeholders for an annual retail gas base rate increase of $ 12 million.

In December 2019, the IUB issued an order approving the settlement with final rates, which were effective January 10, 2020.

In 2021, the IUB issued an order for IPL’s 2020 forward-looking Test Period gas subsequent proceeding, which compared actual revenues and costs to those initially forecasted by IPL, and authorized IPL to maintain its current retail gas rates.

WPL’s Retail Electric and Gas Rate Review (2019/2020 Forward-looking Test Period) - In December 2018, the PSCW issued an order approving WPL’s proposed settlement for its retail electric and gas rate review covering the 2019/2020 Test Period, which was based on a stipulated agreement between WPL and certain stakeholders.

Under the settlement, WPL retail electric and gas base rates did not change from then current levels through the end of 2020.

In September 2020, pursuant to an August 2020 PSCW order, WPL refunded $ 12 million of 2019 fuel-related cost over-collections to its retail electric customers.

In addition, WPL’s amortization of excess deferred taxes resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform was used to offset increases in WPL’s 2020 increased revenue requirements.

WPL’s Retail Electric and Gas Rate Review (2021 Forward-looking Test Period) - In December 2020, the PSCW issued an order authorizing WPL to maintain its then current retail electric and gas base rates, authorized return on common equity, regulatory capital structure and earnings sharing mechanism through the end of 2021.

WPL utilized anticipated fuel-related cost savings and excess deferred income tax benefits in 2021 to offset the revenue requirement impacts of increasing electric and gas rate base, including the Kossuth wind farm, which was placed in service in October 2020, and the expansion of its gas distribution system in Western Wisconsin, which was placed in service in November 2020.

WPL’s Retail Electric and Gas Rate Reviews (2022/2023 Forward-looking Test Period) - In December 2021, the PSCW issued an order authorizing annual base rate increases of $ 114 million and $ 15 million for WPL’s retail electric and gas customers, respectively, covering the 2022/2023 forward-looking Test Period, which was based on a stipulated agreement between WPL and certain stakeholders.

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In addition, the PSCW authorized WPL to receive a recovery of and a return on the remaining net book value of Edgewater Unit 5 through 2023.

Retail electric rate changes were effective on January 1, 2022 and extend through the end of 2023.

WPL's settlement extended, with certain modifications, an earnings sharing mechanism through 2023.

Retail electric rate changes were effective on January 1, 2022 and extended through the end of 2023.

Retail gas rate changes were effective on January 1, 2022 and extended through the end of 2022.

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In December 2022, the PSCW issued an order authorizing an additional annual base rate increase of $ 9 million for WPL’s retail gas customers, covering the 2023 forward-looking Test Period, which reflects changes in weighted average cost of capital, updated depreciation rates and modifications to certain regulatory asset and regulatory liability amortizations.

These retail gas rate changes were effective on January 1, 2023 and extended through the end of 2023.

WPL’s Retail Electric and Gas Rate Reviews (2024/2025 Forward-looking Test Period) - In December 2023, the PSCW issued an order authorizing annual base rate increases of $ 49 million and $ 13 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2024, for the 2024 forward-looking Test Period.

The PSCW’s order also authorized WPL to implement an additional $ 60 million increase in annual rates for its retail electric customers, effective January 1, 2025, for the 2025 forward-looking Test Period.

PROPERTY, PLANT AND EQUIPMENT

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Electric plant:

Generation in service $ 8,060 $ 7,539 $ 4,962 $ 4,922 $ 3,098 $ 2,617

Generation in service (a) $ 9,180 $ 8,060 $ 5,025 $ 4,962 $ 4,155 $ 3,098

Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036

Other in service 567 543 356 354 211 189

Anticipated to be retired early (a) 2,103 2,094 491 487 1,612 1,607

Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612

Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935

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Other plant in service 653 624 411 402 242 222

Accumulated depreciation ( 5,690 ) ( 5,263 ) ( 3,149 ) ( 2,897 ) ( 2,541 ) ( 2,366 )

Accumulated depreciation (b) ( 5,924 ) ( 5,690 ) ( 3,180 ) ( 3,149 ) ( 2,744 ) ( 2,541 )

Net plant 15,210 14,257 7,654 7,846 7,556 6,411

Leased Sheboygan Falls Energy Facility, net (b) — — — — 15 21

Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15

Leased land for solar generation, net 172 133 33 — 139 133

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Non-utility and other:

Non-utility Generation, net (c) 71 75 — — — —

Corporate Services and other, net (d) 423 412 — — — —

Non-utility Generation, net (d) 68 71 — — — —

Corporate Services and other, net (e) 455 423 — — — —

Total non-utility and other 523 494 — — — —

Total property, plant and equipment $ 17,157 $ 16,247 $ 8,298 $ 8,046 $ 8,415 $ 7,722

(a) In 2020, IPL and WPL received approval from MISO to retire Lansing and Edgewater Unit 5, respectively, and currently anticipate retiring Lansing in the first half of 2023 and Edgewater Unit 5 by June 1, 2025.

In 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, and currently anticipates retiring Columbia Units 1 and 2 by June 1, 2026.

Alliant Energy and IPL concluded that Lansing, and Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2, met the criteria to be considered probable of abandonment as of December 31, 2022.

IPL and WPL are currently allowed a full recovery of and a full return on its respective EGUs from both its retail and wholesale customers, and as a result, Alliant Energy, IPL and WPL concluded that no disallowance was required as of December 31, 2022.

As of December 31, 2022, net book values were $ 233 million for Lansing, $ 511 million for Edgewater Unit 5, and $ 440 million for Columbia Units 1 and 2 in aggregate.

(b) Less accumulated amortization of $ 106 million and $ 100 million for WPL as of December 31, 2022 and 2021, respectively.

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(a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $ 180 million.

In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding.

Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $ 1,650 /kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10 %.

Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred.

(b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets.

In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively.

WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026.

Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023.

WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023.

As of December 31, 2023, net book values were $ 504 million for Edgewater Unit 5, and $ 428 million for Columbia Units 1 and 2 in aggregate.

(c) Less accumulated amortization of $ 112 million and $ 106 million for WPL as of December 31, 2023 and 2022, respectively.

Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023.

For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.

(c) Less accumulated depreciation of $ 71 million and $ 67 million for Alliant Energy as of December 31, 2022 and 2021, respectively.

(d) Less accumulated depreciation of $ 75 million and $ 71 million for Alliant Energy as of December 31, 2023 and 2022, respectively.

(e) Less accumulated depreciation of $ 275 million and $ 269 million for Alliant Energy as of December 31, 2023 and 2022, respectively.

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting.

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Non-utility Generation - The Sheboygan Falls Energy Facility was placed in service in 2005 and is depreciated using the straight-line method over a 35 -year period.

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Corporate Services and Other - Property, plant and equipment related to Corporate Services include a customer billing and information system for IPL and WPL and other computer software, and the corporate headquarters building located in Madison, Wisconsin.

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a Mississippi River barge, rail and truck freight terminal in Illinois;

wind turbine blade recycling services;

and a rail-served warehouse in Iowa).

All Corporate Services and Other property, plant and equipment are depreciated using the straight-line method over periods ranging from 5 to 30 years.

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JOINTLY-OWNED ELECTRIC UTILITY PLANT

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Columbia Units 1-2 53.5 % 818 361 6

West Riverside Energy Center and Solar Facility 91.0 % 716 53 2

West Riverside Energy Center and Solar Facility (a) 73.8 % 581 60 6

Forward Wind Energy Center 42.6 % 118 53 —

Alliant Energy $ 2,570 $ 952 $ 33

(a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc.

acquired partial ownership interests in West Riverside.

The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023.

NOTE 5 (a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):

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$ 475 $ 516 $ 242 $ 259 $ 219 $ 244

In 2023, gross write-offs for accounts receivable were as follows (in millions):

Originated in 2022 Originated in 2023

Alliant Energy $ 12 $ 13

NOTE 5 (b) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities.

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Under the Receivables Agreement, IPL has the right to receive cash proceeds, up to a certain limit, from the third party in exchange for the receivables sold.

Effective April 2021, the limit on cash proceeds is $ 110 million.

The limit on cash proceeds fluctuates between $ 5 million and $ 110 million, which IPL may change periodically throughout the year.

As of December 31, 2023, the limit on cash proceeds was $ 5 million and IPL had

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$ 4 million of available capacity under its sales of accounts receivable program.

Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less.

As of December 31, 2022, IPL had $ 30 million of available capacity under its sales of accounts receivable program.

IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions):

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Maximum Average

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Unbilled utility revenues 98 132

Other receivables 1 —

Receivables sold to third party 229 277

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Write-offs, net of recoveries 12 9 9

Effective January 2024, the limit on cash proceeds under the Receivables Agreement is $ 110 million.

Unconsolidated Equity Investments - Alliant Energy’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):

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Refer to Note 17(g) for discussion of a reduction in earnings recorded in 2022 related to a court decision, which is currently expected to reduce the base return on equity authorized for MISO transmission owners, including ATC.

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Non-utility Wind Farm in Oklahoma - The non-utility wind farm located in Oklahoma provides electricity to a third-party under a long-term PPA, and has both cash and tax equity ownership.

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Refer to Note 17(d) for discussion of the guarantee.

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Corporate Venture Investments - Alliant Energy has various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help advance the transition towards a cleaner, more sustainable, and inclusive energy future, by identifying and researching innovative technologies and business models within the emerging energy economy.

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Shares outstanding, January 1 251,134,966 250,474,529 249,868,415

Equity forward agreements — — 4,275,127

At-the-market offering program 4,372,561 — —

Shareowner Direct Plan 454,987 437,669 492,565

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At December 31, 2023, Alliant Energy had a total of 13 million shares available for issuance in the aggregate, pursuant to its 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan.

At-the-Market Offering Program - In December 2022, Alliant Energy filed a prospectus supplement under which it may sell up to $ 225 million of its common stock through an at-the-market offering program.

Alliant Energy has not issued any shares under this program.

Equity Forward Agreements - In 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock.

In 2020, Alliant Energy settled $ 222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $ 51.98 per share.

Alliant Energy used the net proceeds from the settlements for general corporate purposes.

At-the-Market Offering Program - In December 2022, Alliant Energy filed a prospectus supplement to sell up to $ 225 million of its common stock through an at-the-market offering program.

As of December 31, 2023, Alliant Energy issued 4,372,561 shares of common stock through this program and received cash proceeds of $ 223 million, net of $ 2 million in commissions and fees.

The proceeds from the issuances of common stock were used for general corporate purposes.

This at-the-market offering program has expired.

Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market.

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NOTE 9 (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding.

At December 31, 2022, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2026, totaled $ 1 billion ($ 500 million for Alliant Energy at the parent company level, $ 100 million for IPL and $ 400 million for WPL).

At December 31, 2023, the short-term borrowing capacity under a single credit facility agreement totaled $ 1 billion ($ 450 million for Alliant Energy at the parent company level, $ 150 million for IPL and $ 400 million for WPL).

Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $ 500 million, $ 400 million and $ 500 million, respectively, within the $ 1 billion total commitment.

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Weighted average interest rates 5.2 % 2.1 % 5.3 % — % 5.1 % 1.6 %

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In January 2024, Alliant Energy, IPL and WPL extended their single credit facility agreement, which currently expires in December 2028, and reallocated credit facility capacity amounts to $ 350 million for Alliant Energy at the parent company level, $ 150 million for IPL and $ 500 million for WPL, within the $ 1 billion total commitment.

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NOTE 9 (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):

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400 400 — 400 400 —

5.7 %, due 2033 (b)

300 300 — — — —

6.45 %, due 2033

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300 — 300 300 — 300

3.95 %, due 2032 (b)

3.95 %, due 2032

600 — 600 600 — 600

4.95 % due 2033 (c)

300 — 300 — — —

6.25 %, due 2034

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350 — 350 350 — 350

2.25 % (Retired in 2022)

3,100 — 3,100 2,800 — 2,800

AEF term loan credit agreement through March 2024, 6 % at December 31, 2023 (with Alliant Energy as guarantor) (d)

300 — — 400 — —

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200 — — 200 — —

AEF term loan credit agreement through March 2024, 5 % at December 31, 2022 (with Alliant Energy as guarantor) (c)

400 — — — — —

AEF 1.4 % senior notes, due 2026 (with Alliant Energy as guarantor) (a)

Alliant Energy 3.875 % convertible senior notes, due 2026 (e)

575 — — — — —

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300 — — 300 — —

AEF 3.6 % senior notes, due 2032 (with Alliant Energy as guarantor) (a)(d)

AEF 5.95 % senior notes, due 2029 (with Alliant Energy as guarantor) (a)(f)

300 — — — — —

Sheboygan Power, LLC 5.06 % senior secured notes, due 2023 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)

AEF 3.6 % senior notes, due 2032 (with Alliant Energy as guarantor) (a)

350 — — 350 — —

AEF term loan credit agreement, 1 % at December 31, 2021 (with Alliant Energy as guarantor) (Retired in 2022)

Sheboygan Power, LLC 5.06 % senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)

AEF 3.75 % senior notes (with Alliant Energy as guarantor) (Retired in 2023)

— — — 400 — —

Corporate Services 3.45 % senior notes (Retired in 2022)

Other, 1 % at December 31, 2023, due 2024 to 2025

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Unamortized debt (discount) and premium, net ( 21 ) ( 9 ) ( 11 ) ( 22 ) ( 8 ) ( 11 )

Long-term debt, net (e) $ 7,668 $ 3,646 $ 2,770 $ 6,735 $ 3,643 $ 2,179

Long-term debt, net (g) $ 8,225 $ 3,445 $ 3,070 $ 7,668 $ 3,646 $ 2,770

(a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer.

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Treasury rates at the time of redemption.

(b) In August 2022, WPL issued $ 600 million of 3.95 % debentures due 2032.

The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds were disbursed for the development and acquisition of WPL’s solar EGUs.

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(c) In March 2022, AEF entered into a $ 300 million variable rate term loan credit agreement and used the borrowings under this agreement to retire its $ 300 million variable rate term loan credit agreement that expired in March 2022.

In December 2022, AEF increased the amount outstanding under the new term loan credit agreement by $ 100 million and used the additional borrowings to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

In January 2023, AEF entered into a $ 300 million interest rate swap maturing in January 2026.

Under the terms of the swap, AEF exchanged variable rate borrowings for a fixed rate of 3.93 %.

(d) In February 2022, AEF issued $ 350 million of 3.6 % senior notes due 2032.

The net proceeds from the issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

(e) There were no significant sinking fund requirements related to the outstanding long-term debt.

In December 2022, AEF entered into a $ 50 million variable rate term loan credit agreement (with Alliant Energy as guarantor), which expires in January 2024.

AEF received the proceeds from the issuance in January 2023, and used the borrowings under this agreement to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

(b) In September 2023, IPL issued $ 300 million of 5.7 % senior debentures due 2033.

The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments.

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The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of its solar EGUs.

(d) In January 2023, AEF entered into a $ 300 million interest rate swap maturing in January 2026 to mitigate interest rate risk.

Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93 % on a portion of its variable-rate term loan borrowings.

In December 2023, AEF retired the remaining $ 100 million variable-rate term loan borrowings.

Refer to Note 15 for additional information on the interest rate swap.

(e) Refer to “ Convertible Senior Notes ” below for additional information.

(f) In November 2023, AEF issued $ 300 million of 5.95 % senior notes due 2029.

The net proceeds from AEF’s issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

(g) There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes - In March 2023, Alliant Energy issued $ 575 million of 3.875 % convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes.

The Notes will mature on March 15, 2026 unless earlier converted or repurchased.

Alliant Energy may not redeem the Notes prior to the maturity date.

Holders may convert their Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

• during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130 % of the conversion price on each applicable trading day during such period;

• during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $ 1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day;

• upon the occurrence of specified corporate events.

On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their Notes at any time, regardless of the foregoing circumstances.

Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $ 1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $ 64.32 per share of Alliant Energy’s common stock).

The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest.

In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100 % of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2023, the conditions allowing holders of the Notes to convert their Notes were not met, and as a result, the Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet.

As of December 31, 2023, the net carrying amount of the Notes was $ 568 million, with unamortized debt issuance costs of $ 7 million, and the estimated fair value (Level 2) of the Notes was $ 572 million.

As of December 31, 2023, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes.

Five-Year Schedule of Long-term Debt Maturities - At December 31, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions):

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AEF 309 — 200 — 300

Alliant Energy parent company — — 575 — —

Alliant Energy $ 809 $ 300 $ 775 $ 300 $ 800

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Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.

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Weighted average discount rate 4 % 4 % 4 % 4 % 4 % 4 %

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business through 2025, the initial lease term.

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business.

WPL is responsible for the operation of the EGU and has exclusive rights to its output.

This finance lease contains two lease renewal periods, which are not included in the finance lease obligation, as well as an option to purchase the facility at the end of the initial lease term.

In 2023, WPL renewed this financing lease through 2039.

This lease contains one remaining lease renewal period, which is not included in the finance lease obligation.

For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to its investments in solar generation, WPL entered into land lease agreements with unaffiliated parties that commenced in 2021 and 2022.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced.

The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities.

The leases do not contain purchase options and are fixed lease payments.

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Finance lease details are as follows (dollars in millions):

December 31, 2023 December 31, 2022

Alliant Energy WPL Alliant Energy WPL

Alliant Energy IPL WPL Alliant Energy IPL WPL

Property, plant and equipment, net:

Sheboygan Falls Energy Facility n/a $ 15 n/a $ 21

Sheboygan Falls Energy Facility N/A N/A $ 79 N/A N/A $ 15

Leased land for solar generation $ 172 $ 33 139 $ 133 $ — 133

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Other current liabilities:

Sheboygan Falls Energy Facility n/a $ 12 n/a $ 10

Sheboygan Falls Energy Facility N/A N/A $ 11 N/A N/A $ 12

Leased land for solar generation $ — $ — — $ 5 $ — 5

— — 11 5 — 17

Other liabilities:

Sheboygan Falls Energy Facility n/a 19 n/a 31

Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19

Leased land for solar generation 172 33 139 131 — 131

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Total finance lease liabilities $ 172 $ 33 $ 228 $ 136 $ — $ 167

Weighted average remaining lease term 34 years 28 years 34 years 10 years

Weighted average discount rate 5 % 5 % 3 % 9 %

Alliant Energy WPL

Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years

Weighted average discount rate 5 % 5 % 5 % 5 % N/A 5 %

Alliant Energy IPL WPL

2023 2022 2021 2023 2022 2021 2023 2022 2021

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Total finance lease expense $ 7 $ 3 $ — $ 1 $ — $ — $ 14 $ 13 $ 11

In 2022, Alliant Energy’s and WPL’s finance lease liabilities arising from obtaining leased assets were $ 125 million, which represent non-cash financing activities.

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):

Alliant Energy IPL WPL

2023 2022 2023 2022 2023 2022

Finance lease liabilities arising from obtaining leased assets

$ 34 $ 125 $ 33 $ — $ 71 $ 125

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Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions):

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Alliant Energy 8 8 8 8 8 320 360 188 172

IPL 2 2 2 2 2 59 69 36 33

WPL 21 17 13 13 13 334 411 183 228

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This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values.

FERC also allows IPL and WPL to enter into power supply agreements with

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municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa;

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and a rail-served warehouse in Iowa.

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Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions):

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Investment tax credits ( 1 ) ( 1 ) ( 1 ) ( 1 ) — — — — ( 1 )

Provision recorded as a change in accrued interest ( 1 ) — — ( 1 ) — — — — —

$ 4 $ 22 ($ 74 ) ($ 58 ) ($ 50 ) ($ 36 ) $ 60 $ 66 ($ 51 )

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Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.

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Federal credit carryforwards 649 672 449 450 191 209

Net operating losses carryforwards - federal — 39 — 36 — —

Net operating losses carryforwards - state 26 32 1 — — —

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Federal tax credits 2031-2043 649 449 191

Valuation Allowances - In 2022, Alliant Energy fully utilized its federal net operating losses carryforwards.

This allowed for the utilization of federal tax credit carryforwards prior to their expiration, resulting in the reversal of Alliant Energy’s valuation allowances in 2022.

Valuation Allowances - Refer to N ote 1 (c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions.

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(a) The 2020 and 2021 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return.

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Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12 % to 9.8 %, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.

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These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5 %, compared to the 9.8 % Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted.

In September 2022, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4 %, effective January 1, 2023.

In September 2022 and September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4 % effective January 1, 2023, and 7.1 % effective January 1, 2024, respectively.

Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled.

Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured based upon the new rate effective January 1, 2023, which resulted in a $ 77 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a decrease in their deferred tax liabilities in 2022.

Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $ 77 million and $ 74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively.

The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2023, which resulted in a charge of $ 8 million recorded to income tax expense in Alliant Energy’s income statement and a decrease in deferred income tax assets on Alliant Energy’s balance sheet in 2022.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in charges of $ 8 million and $ 10 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022 and 2023, respectively.

Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

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Rate of compensation increase 3.30 % 3.30 % 3.30 % N/A N/A N/A

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Qualified Defined Benefit Pension Plan OPEB Plans

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Rate of compensation increase 3.30 % 3.30 % 3.30 % N/A N/A N/A

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Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations.

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Expected return on plan assets (a) ( 22 ) ( 31 ) ( 31 ) ( 1 ) ( 1 ) —

Amortization of prior service credit (b) — — — — — ( 1 )

Amortization of actuarial loss (c) 13 15 19 1 2 2

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(b) Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

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(c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

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In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $ 7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

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Benefit Plan Assets and Obligations - A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):

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Plan participants’ contributions — — 4 4

Actuarial gain ( 269 ) ( 46 ) ( 37 ) ( 12 )

Actuarial (gain) loss 23 ( 269 ) ( 3 ) ( 37 )

Gross benefits paid ( 74 ) ( 152 ) ( 20 ) ( 18 )

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$ 335 $ 373 $ 11 $ 20

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Defined Benefit Pension Plans OPEB Plans

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Plan participants’ contributions — — 2 2

Actuarial gain ( 123 ) ( 23 ) ( 14 ) ( 4 )

Actuarial (gain) loss 9 ( 123 ) ( 1 ) ( 14 )

Gross benefits paid ( 35 ) ( 77 ) ( 8 ) ( 7 )

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Under funded status at December 31 ($ 35 ) ($ 45 ) ($ 4 ) ($ 10 )

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Defined Benefit Pension Plans OPEB Plans

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Plan participants’ contributions — — 2 2

Actuarial gain ( 117 ) ( 18 ) ( 13 ) ( 5 )

Actuarial (gain) loss 10 ( 117 ) ( 2 ) ( 13 )

Gross benefits paid ( 32 ) ( 67 ) ( 8 ) ( 8 )

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Under funded status at December 31 ($ 75 ) ($ 90 ) ($ 47 ) ($ 51 )

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Defined Benefit Pension Plans OPEB Plans

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$ 148 $ 165 $ 3 $ 6

Actuarial gains related to benefit obligations in 2022 and 2021 for defined benefit pension and OPEB plans were primarily due to increases in the discount rates.

In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates.

In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates.

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Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):

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Regulatory assets $ 28 $ 30 $ 24 $ 25

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Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):

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$ 90 $ 90 $ 90 $ 91 $ 90 $ 408

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IPL 2024 2025 2026 2027 2028 2029 - 2033

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Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term.

Investment risk of plan assets is mitigated through diversification, including U.S.

and international equity, fixed income and global asset strategies.

Investment risk of plan assets is mitigated through diversification, including equity, fixed income and global asset strategies.

Global asset strategies may include investments in global equity, global debt and currencies.

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For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities.

The allocations shown below exclude market exposure obtained through the overlay management service and cash held at IPL's qualified defined benefit pension plan as a result of a contribution made late in 2022.

The allocations shown below exclude market exposure obtained through the overlay management service.

At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

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Cash and equivalents 0 % - 5 % 2 %

Equity securities - U.S.

14 % - 61 % 33 %

Equity securities - international 11 % - 31 % 21 %

Equity securities 47 % - 67 % 56 %

Global asset securities 0 % - 15 % 5 %

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Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts.

The investment strategy of the Corporate Services 401(h) assets mirrors those of the defined benefit pension plans, which are discussed above.

For VEBA trusts with assets greater than $ 5 million and the WPL 401(h) assets, the mix among asset classes is governed by allocation targets.

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At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $ 5 million and the WPL 401(h) assets were as follows:

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Target Range Actual

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Cash and equivalents 0 % - 5 % 1 %

Equity securities - U.S.

0 % - 55 % 35 %

Equity securities 0 % - 55 % 36 %

Fixed income securities 40 % - 100 % 63 %

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These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets.

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At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

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Cash and equivalents $ 19 $ — $ 19 $ — $ 79 $ — $ 79 $ —

Equity securities - U.S.

185 185 — — 256 256 — —

Equity securities 223 223 — — 185 185 — —

Global asset securities 39 39 — — 35 35 — —

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Accrued investment income 2 1

Due to brokers, net (pending trades with brokers) — ( 1 )

Total pension plan assets $ 732 $ 706

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Cash and equivalents $ 9 $ — $ 9 $ — $ 62 $ — $ 62 $ —

Equity securities - U.S.

83 83 — — 117 117 — —

Equity securities 107 107 — — 83 83 — —

Global asset securities 19 19 — — 16 16 — —

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Cash and equivalents $ 8 $ — $ 8 $ — $ 13 $ — $ 13 $ —

Equity securities - U.S.

82 82 — — 114 114 — —

Equity securities 93 93 — — 82 82 — —

Global asset securities 16 16 — — 16 16 — —

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Total pension plan assets $ 306 $ 291

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At December 31, the fair values of OPEB plan assets were as follows (in millions):

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Cash and equivalents $ 9 $ — $ 9 $ — $ 3 $ — $ 3 $ —

Equity securities - U.S.

9 9 — — 11 11 — —

Equity securities 8 8 — — 9 9 — —

Global asset securities — — — — 1 1 — —

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Cash and equivalents $ 1 $ — $ 1 $ — $ 1 $ — $ 1 $ —

Equity securities - U.S.

5 5 — — 8 8 — —

Equity securities 6 6 — — 5 5 — —

Fixed income securities 36 36 — — 34 34 — —

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Total OPEB plan assets $ 61 $ 58

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Fair Level Level Level Fair Level Level Level

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Cash and equivalents $ 1 $ — $ 1 $ — $ — $ — $ — $ —

Equity securities - U.S.

1 1 — — 1 1 — —

Equity securities 2 2 — — 1 1 — —

Fixed income securities 11 11 — — 13 13 — —

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NOTE 13 (b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees.

The 2020 OIP replaced the Amended and Restated 2010 OIP, which permitted similar grants.

At December 31, 2022, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP and the Amended and Restated 2010 OIP, and 8 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP.

At December 31, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP.

Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock.

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As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $ 8 million, $ 4 million and $ 3 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years .

Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income

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Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements.

As of December 31, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

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Nonvested awards, December 31 233,954 52.60 190,273 54.13 196,429 51.59

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Restricted Stock Units - Equity Awards - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period.

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Nonvested units, December 31 234,259 52.58 198,275 54.53 217,819 50.54

Performance Restricted Stock Units - Equity Awards - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 grants.

The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200 % of the target number of units under each award type.

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Nonvested units, December 31 257,639 52.76 199,874 54.74 196,429 50.74

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NOTE 13 (c) Deferred Compensation Plan - Alliant Energy maintains a DCP under which key employees may defer up to 100 % of base salary and short-term cash incentive compensation and members of its Board of Directors may elect to defer all or part of their retainer and committee fees.

NOTE 13 (c) Deferred Compensation Plan - Alliant Energy maintains a DCP under which certain key employees may defer up to 100 % of base salary and short-term cash incentive compensation and members of its Board of Directors may elect to defer all or part of their retainer and committee fees.

Key employees who have made the maximum allowed contribution to the Alliant Energy 401(k) Savings Plan may receive an additional credit to the DCP.

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At December 31, 2023 and 2022, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $ 21 million and $ 19 million, respectively.

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ASSET RETIREMENT OBLIGATIONS

Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, wind farms, ash ponds, active ash landfills, solar generation, coal yards, above ground storage tanks and batteries.

Recognized AROs relate to legal obligations for the removal, closure, dismantlement and management of several assets including, but not limited to, wind farms, active ash landfills, ash ponds, solar generation, above ground storage tanks and batteries.

Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls.

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Commodity Derivatives -

Purpose - Derivative instruments were used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and rail transportation costs.

Purpose - Derivative instruments were utilized for risk management purposes to mitigate pricing volatility for fuel used to supply natural gas-fired EGUs, natural gas supplied to retail customers, and purchased electricity, as well as optimize the value of natural gas pipeline capacity and electric generation, which may include swap, physical forward and option contracts.

In addition, FTRs help manage transmission congestion costs in the MISO market.

Risk policies are maintained that govern the use of such derivative instruments.

Derivative instruments were not designated as hedging instruments and included the following:

Risk management purpose Type of instrument

Mitigate pricing volatility for:

Fuel used to supply natural gas-fired EGUs Natural gas swap, options and physical forward contracts (IPL and WPL)

Natural gas supplied to retail customers Natural gas swap, options and physical forward contracts (IPL and WPL)

Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL)

Electric generation and load Electric swap contracts (IPL and WPL)

Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL)

Natural gas swap contracts (IPL)

Optimize the value of electric generation Electric swap contracts (IPL and WPL)

Manage transmission congestion costs FTRs (IPL and WPL)

Manage rail transportation costs Diesel fuel swap contracts (WPL)

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Notional Amounts - As of December 31, 2023, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

Electricity FTRs Natural Gas Coal

MWhs Years MWhs Years Dths Years Tons Years

Electricity FTRs Natural Gas

MWhs Years MWhs Years Dths Years

Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032

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Non-current derivative liabilities 47 20 8 6 39 14

In 2022, Alliant Energy’s, IPL’s and WPL’s derivative assets increased primarily as a result of higher natural gas prices.

Alliant Energy’s, IPL’s and WPL’s derivative liabilities increased primarily due to new natural gas contracts entered into in 2022 and declining natural gas prices subsequent to the execution of the new contracts.

In 2023, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of natural gas and electricity contracts, and lower natural gas prices.

Alliant Energy’s, IPL’s and WPL’s non-current derivative liabilities increased primarily due to lower natural gas prices.

Alliant Energy’s and IPL’s current derivative liabilities decreased primarily due to settlements of natural gas contracts.

Based on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

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At December 31, 2023 and 2022, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

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Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets.

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Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Interest Rate Derivative - In January 2023, AEF entered into a $ 300 million interest rate swap maturing in January 2026 to mitigate interest rate risk.

Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93 % on a portion of its variable-rate term loan borrowings.

The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts.

As of December 31, 2023, $ 1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet.

This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss.

As of December 31, 2023, accumulated other comprehensive income included $ 1 million of income related to the interest rate swap.

In 2023, $ 3 million of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.

FAIR VALUE MEASUREMENTS

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Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date.

Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting

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Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation.

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Refer to Note 5(b) for additional information regarding deferred proceeds.

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Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on a discounted cash flow methodology using observable data from comparably traded securities with similar credit profiles, and was substantially classified as Level 2.

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Money market fund investments $ 45 $ 45 $ — $ — $ 45 $ 10 $ 10 $ — $ — $ 10

Derivatives 237 — 206 31 237 176 — 146 30 176

Commodity derivatives 88 — 59 29 88 237 — 206 31 237

Interest rate derivatives 1 — 1 — 1 — — — — —

Deferred proceeds 216 — — 216 216 185 — — 185 185

Liabilities and equity:

Derivatives 79 — 67 12 79 9 — 8 1 9

Commodity derivatives 98 — 93 5 98 79 — 67 12 79

Long-term debt (incl.

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Money market fund investments $ 45 $ 45 $ — $ — $ 45 $ 10 $ 10 $ — $ — $ 10

Derivatives 138 — 111 27 138 84 — 65 19 84

Commodity derivatives 54 — 30 24 54 138 — 111 27 138

Deferred proceeds 216 — — 216 216 185 — — 185 185

Liabilities and equity:

Derivatives 46 — 35 11 46 4 — 3 1 4

Long-term debt 3,646 — 3,228 — 3,228 3,643 — 4,124 — 4,124

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Commodity derivatives 30 — 25 5 30 46 — 35 11 46

Long-term debt (incl.

current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228

WPL 2023 2022

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Amount 1 2 3 Total Amount 1 2 3 Total

Derivatives $ 99 $ — $ 95 $ 4 $ 99 $ 92 $ — $ 81 $ 11 $ 92

Commodity derivatives $ 34 $ — $ 29 $ 5 $ 34 $ 99 $ — $ 95 $ 4 $ 99

Liabilities and equity:

Derivatives 33 — 32 1 33 5 — 5 — 5

Long-term debt (incl.

current maturities) 2,770 — 2,542 — 2,542 2,429 — 2,862 — 2,862

Commodity derivatives 68 — 68 — 68 33 — 32 1 33

Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

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The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $ 3 ($ 18 ) $ — $ —

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IPL Commodity Contract Derivative

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(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

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Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivativ e assets (liabiliti es) at December 31 as follows (in millions):

Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions):

Alliant Energy IPL WPL

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COMMITMENTS AND CONTINGENCIES

At December 31, 2022, Alliant Energy’s and WPL’s minimum future commitments in 2023 for these projects were $ 184 million and $ 180 million, respectively.

NOTE 17 (a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of solar generation, WPL’s expansion of battery storage, and IPL’s repowering of the existing Franklin County wind farm.

At December 31, 2023, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2024 for these projects were $ 188 million, $ 131 million, and $ 57 million, respectively.

NOTE 17 (b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers.

In addition, there are various purchase commitments associated with other goods and services.

At December 31, 2022, the related minimum future commitments were as follows (in millions):

At December 31, 2023, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):

Alliant Energy 2024 2025 2026 2027 2028 Thereafter Total

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$ 237 $ 123 $ 57 $ 45 $ 22 $ 47 $ 531

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WPL 2024 2025 2026 2027 2028 Thereafter Total

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Alliant Energy estimates its expected loss to be a portion of the $ 49 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners.

Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay;

however, as of both December 31, 2022 and 2021, a liability of $ 5 million is recorded in “Other liabilities” on Alliant Energy’s balance sheets for expected credit losses related to the contingent obligations that are in the scope of these guarantees.

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Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2023 and 2022.

Whiting Petroleum completed a business combination with Oasis Petroleum Inc.

in July 2022.

The combined operations are now known as Chord Energy Corporation.

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Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2023 and 2022.

Transfers of Renewable Tax Credits - In 2023, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery storage facilities to other corporate taxpayers in exchange for cash.

IPL and WPL provided indemnifications associated with $ 76 million and $ 22 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in 2023 in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements.

Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

NOTE 17 (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations.

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IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment.

At December 31, 2022, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions).

At December 31, 2022, such amounts for WPL were not material.

Alliant Energy IPL

At December 31, 2023, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the

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MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):

Alliant Energy IPL WPL

Range of estimated future costs $ 9 - $ 36 $ 5 - $ 11 $ 4 - $ 25

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Refer to Notes 5(a) and 15 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.

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NOTE 17 (g) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with FERC requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC and ATC.

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In 2020, FERC issued orders in response to various rehearing requests and increased the base return on equity authorized for the MISO transmission owners from 9.88 % to 10.02 % for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016.

In August 2022, the U.S.

Court of Appeals for the District of Columbia Circuit vacated FERC’s prior orders that established the base return on equity authorized for the MISO transmission owners and remanded the cases to FERC for further proceedings, which may result in additional changes to the base return on equity authorized for the MISO transmission owners.

As a result of the August 2022 court decision, Alliant Energy recorded a $ 6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the anticipated reduction in the base return on equity authorized for the MISO transmission owners.

In 2022, the U.S.

Court of Appeals for the District of Columbia vacated FERC’s prior orders that established the base return on equity authorized for the MISO transmission owners and remanded the cases to FERC for further proceedings, which may result in additional changes to the base return on equity authorized for the MISO transmission owners.

As a result of the 2022 court decision, Alliant Energy recorded a $ 6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the anticipated reduction in the base return on equity authorized for the MISO transmission owners.

Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.

NOTE 17 (h) Collective Bargaining Agreements - At December 31, 2023, employees covered by collective bargaining agreements represented 53 %, 69 % and 83 % of total employees of Alliant Energy, IPL and WPL, respectively.

In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18 % and 53 % of total employees of Alliant Energy and IPL, respectively.

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SEGMENTS OF BUSINESS

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Income taxes 2 2 4

Net income attributable to Alliant Energy common shareowners 675 11 686

Net income (loss) attributable to Alliant Energy common shareowners 711 ( 8 ) 703

Total assets 17,833 1,684 606 20,123 1,114 21,237

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Depreciation and amortization 601 56 7 664 7 671

Operating income (loss) 716 63 ( 11 ) 768 27 795

Operating income 805 97 3 905 23 928

Interest expense 269 56 325

Equity income from unconsolidated investments, net ( 1 ) — — ( 1 ) ( 50 ) ( 51 )

Income tax expense (benefit) ( 87 ) 13 ( 74 )

Income taxes 16 6 22

Net income attributable to Alliant Energy common shareowners 675 11 686

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Construction and acquisition expenditures 1,318 74 — 1,392 92 1,484

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ATC Holdings,

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Construction and acquisition expenditures 980 90 — 1,070 99 1,169

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IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments:

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Depreciation and amortization 342 32 7 381

Operating income (loss) 420 43 ( 3 ) 460

Operating income 397 53 3 453

Interest expense 148

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Depreciation and amortization 338 31 6 375

Operating income 358 50 2 410

Operating income (loss) 420 43 ( 3 ) 460

Interest expense 139

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Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions):

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2023 Electric Gas Other Total

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Construction and acquisition expenditures 970 49 — 1,019

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2022 Electric Gas Other Total

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Depreciation and amortization 259 24 — 283

Operating income (loss) 296 20 ( 8 ) 308

Operating income 408 44 — 452

Interest expense 121

Income tax benefit ( 51 )

Income taxes 66

Net income 315

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WPL billings to ATC 20 18 18

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As of December 31, 2023 and 2022, WPL owed ATC net amounts of $ 10 million and $ 10 million, respectively.

In 2020, WPL received $ 46 million from ATC related to construction deposits WPL previously provided ATC for transmission network upgrades for West Riverside, which is substantially recorded in “Other” in Alliant Energy’s and WPL’s cash flows from investing activities.

WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 10 for discussion of WPL’s Sheboygan Falls Energy Facility lease.

CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE

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Compared sentence by sentence after normalising whitespace, quotation marks, case and digits, so re-formatting and restated figures do not read as changed language. Wording changes appear as one removal and one addition. The current filing and the prior one are authoritative.

What changed 10-K

Item 8. Financial Statements and Supplementary Data