Alliant Energy (LNT) 10-Q 3 May 24 2024 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	3 Months Ended
	Mar. 31, 2024 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	0000352541
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	1-9894
Entity Tax Identification Number	39-1380265
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	LNT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	256,379,032
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
IPL [Member]
Entity Information [Line Items]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Incorporation, State or Country Code	IA
Entity Address, Address Line One	Alliant Energy Tower
Entity Address, City or Town	Cedar Rapids
Entity Address, State or Province	IA
Entity Address, Postal Zip Code	52401
City Area Code	319
Local Phone Number	786-4411
Entity File Number	1-4117
Entity Tax Identification Number	42-0331370
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Information [Line Items]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	0-337
Entity Tax Identification Number	39-0714890
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues:
Electric utility	$ 791	$ 768
Gas utility	205	276
Other utility	13	11
Non-utility	22	22
Total revenues	1,031	1,077
Operating expenses:
Electric production fuel and purchased power	163	157
Electric transmission service	152	146
Cost of gas sold	114	181
Other operation and maintenance	160	174
Depreciation and amortization	189	166
Taxes other than income taxes	31	31
Total operating expenses	809	855
Operating income	222	222
Other (income) and deductions:
Interest expense	107	94
Equity income from unconsolidated investments, net	(15)	(17)
Allowance for funds used during construction	(19)	(19)
Other	1	3
Total other (income) and deductions	74	61
Income before income taxes	148	161
Income tax expense (benefit)	(10)	(2)
Net income	158	163
Net income attributable to common shareowners	$ 158	$ 163
Weighted average number of common shares outstanding:
Basic (in shares)	256,200	251,200
Diluted (in shares)	256,500	251,400
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.62	$ 0.65
Diluted (in dollars per share)	$ 0.62	$ 0.65
IPL [Member]
Revenues:
Electric utility	$ 392	$ 388
Gas utility	108	150
Other utility	13	11
Total revenues	513	549
Operating expenses:
Electric production fuel and purchased power	67	47
Electric transmission service	103	104
Cost of gas sold	60	95
Other operation and maintenance	86	95
Depreciation and amortization	96	96
Taxes other than income taxes	16	16
Total operating expenses	428	453
Operating income	85	96
Other (income) and deductions:
Interest expense	42	37
Allowance for funds used during construction	(10)	(3)
Other	0	1
Total other (income) and deductions	32	35
Income before income taxes	53	61
Income tax expense (benefit)	(10)	(11)
Net income	63	72
WPL [Member]
Revenues:
Electric utility	399	380
Gas utility	97	126
Total revenues	496	506
Operating expenses:
Electric production fuel and purchased power	96	109
Electric transmission service	49	42
Cost of gas sold	53	86
Other operation and maintenance	63	66
Depreciation and amortization	90	68
Taxes other than income taxes	14	14
Total operating expenses	365	385
Operating income	131	121
Other (income) and deductions:
Interest expense	41	36
Allowance for funds used during construction	(9)	(16)
Other	1	1
Total other (income) and deductions	33	21
Income before income taxes	98	100
Income tax expense (benefit)	6	12
Net income	$ 92	$ 88

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 32	$ 62
Accounts receivable, less allowance for expected credit losses	426	475
Production fuel, at weighted average cost	60	62
Gas stored underground, at weighted average cost	52	79
Materials and supplies, at weighted average cost	208	202
Regulatory assets	218	232
Other	112	160
Total current assets	1,108	1,272
Property, plant and equipment, net	17,354	17,157
Investments:
ATC Holdings	392	386
Other	219	216
Total investments	611	602
Other assets:
Regulatory assets	2,002	2,029
Deferred charges and other	173	177
Total other assets	2,175	2,206
Total assets	21,248	21,237
Current liabilities:
Current maturities of long-term debt	809	809
Commercial paper	334	475
Accounts payable	438	611
Regulatory liabilities	100	107
Other	303	302
Total current liabilities	1,984	2,304
Long-term debt, net (excluding current portion)	8,524	8,225
Other liabilities:
Deferred tax liabilities	2,038	2,042
Regulatory liabilities	1,036	1,023
Pension and other benefit obligations	245	249
Other	604	617
Total other liabilities	3,923	3,931
Commitments and contingencies (Note 13)
Common equity:
Common stock	3	3
Additional paid-in capital	3,033	3,030
Retained earnings	3,791	3,756
Accumulated other comprehensive income	2	1
Shares in deferred compensation trust - 341,937 and 379,006 shares at a weighted average cost of $34.96 and $34.48 per share	(12)	(13)
Total common equity	6,817	6,777
Total liabilities and equity	21,248	21,237
IPL [Member]
Current assets:
Cash and cash equivalents	12	53
Accounts receivable, less allowance for expected credit losses	204	242
Production fuel, at weighted average cost	29	27
Gas stored underground, at weighted average cost	17	35
Materials and supplies, at weighted average cost	126	122
Regulatory assets	85	93
Other	42	51
Total current assets	515	623
Property, plant and equipment, net	8,450	8,298
Other assets:
Regulatory assets	1,482	1,484
Deferred charges and other	85	84
Total other assets	1,567	1,568
Total assets	10,532	10,489
Current liabilities:
Current maturities of long-term debt	500	500
Accounts payable	213	262
Accrued taxes	61	50
Accrued interest	49	40
Regulatory liabilities	79	72
Other	97	101
Total current liabilities	999	1,025
Long-term debt, net (excluding current portion)	3,445	3,445
Other liabilities:
Deferred tax liabilities	1,098	1,091
Regulatory liabilities	569	572
Pension and other benefit obligations	49	51
Other	335	331
Total other liabilities	2,051	2,045
Commitments and contingencies (Note 13)
Common equity:
Common stock	33	33
Additional paid-in capital	2,937	2,887
Retained earnings	1,067	1,054
Total common equity	4,037	3,974
Total liabilities and equity	10,532	10,489
WPL [Member]
Current assets:
Cash and cash equivalents	11	7
Accounts receivable, less allowance for expected credit losses	209	219
Production fuel, at weighted average cost	31	35
Gas stored underground, at weighted average cost	35	44
Materials and supplies, at weighted average cost	78	77
Regulatory assets	133	139
Prepaid gross receipts tax	38	49
Other	19	43
Total current assets	554	613
Property, plant and equipment, net	8,450	8,415
Other assets:
Regulatory assets	520	545
Deferred charges and other	57	61
Total other assets	577	606
Total assets	9,581	9,634
Current liabilities:
Commercial paper	0	318
Accounts payable	174	293
Accrued interest	42	40
Regulatory liabilities	21	35
Other	105	89
Total current liabilities	342	775
Long-term debt, net (excluding current portion)	3,367	3,070
Other liabilities:
Deferred tax liabilities	811	827
Regulatory liabilities	467	451
Pension and other benefit obligations	119	121
Other	480	493
Total other liabilities	1,877	1,892
Commitments and contingencies (Note 13)
Common equity:
Common stock	66	66
Additional paid-in capital	2,533	2,478
Retained earnings	1,396	1,353
Total common equity	3,995	3,897
Total liabilities and equity	$ 9,581	$ 9,634

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	256,379,032	256,096,848
Shares in deferred compensation trust (in shares)	341,937	379,006
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 34.96	$ 34.48
IPL [Member]
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed Consolidated Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net income	$ 158	$ 163
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	189	166
Other	(18)	(6)
Other changes in assets and liabilities:
Accounts receivable	(116)	(86)
Gas stored underground	27	68
Derivative assets	30	115
Regulatory assets	35	(32)
Accounts payable	12	(97)
Regulatory liabilities	(14)	(95)
Other	4	(8)
Net cash flows from operating activities	307	188
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(478)	(417)
Other construction and acquisition expenditures	(32)	(34)
Cash receipts on sold receivables	155	173
Proceeds from sale of partial ownership interest in West Riverside	0	25
Other	2	(10)
Net cash flows from (used for) investing activities	(353)	(263)
Cash flows from (used for) financing activities:
Common stock dividends	(123)	(113)
Proceeds from issuance of long-term debt	597	862
Payments to retire long-term debt	(300)	0
Net change in commercial paper and other short-term borrowings	(141)	(532)
Other	(15)	(5)
Net cash flows from (used for) financing activities	18	212
Net increase (decrease) in cash, cash equivalents and restricted cash	(28)	137
Cash, cash equivalents and restricted cash at beginning of period	63	24
Cash, cash equivalents and restricted cash at end of period	35	161
Supplemental cash flows information:
Interest	(97)	(93)
Income taxes, net	(2)	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	204	254
Beneficial interest obtained in exchange for securitized accounts receivable	184	153
IPL [Member]
Cash flows from operating activities:
Net income	63	72
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	96	96
Other	(11)	1
Other changes in assets and liabilities:
Accounts receivable	(119)	(106)
Gas stored underground	18	34
Derivative assets	20	69
Accounts payable	(7)	(56)
Regulatory liabilities	4	(59)
Other	12	(27)
Net cash flows from operating activities	76	24
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(253)	(101)
Cash receipts on sold receivables	155	173
Other	(9)	(2)
Net cash flows from (used for) investing activities	(107)	70
Cash flows from (used for) financing activities:
Common stock dividends	(50)	(70)
Capital contributions from parent	50	0
Other	(10)	(4)
Net cash flows from (used for) financing activities	(10)	(74)
Net increase (decrease) in cash, cash equivalents and restricted cash	(41)	20
Cash, cash equivalents and restricted cash at beginning of period	53	15
Cash, cash equivalents and restricted cash at end of period	12	35
Supplemental cash flows information:
Interest	(32)	(37)
Income taxes, net	(2)	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	110	98
Beneficial interest obtained in exchange for securitized accounts receivable	184	153
WPL [Member]
Cash flows from operating activities:
Net income	92	88
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	90	68
Other	(11)	(12)
Other changes in assets and liabilities:
Gas stored underground	9	35
Derivative assets	12	46
Regulatory assets	29	(37)
Accounts payable	15	(48)
Derivative liabilities	(4)	28
Regulatory liabilities	(18)	(35)
Other	27	52
Net cash flows from operating activities	241	185
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(225)	(316)
Proceeds from sale of partial ownership interest in West Riverside	0	25
Other	12	(4)
Net cash flows from (used for) investing activities	(213)	(295)
Cash flows from (used for) financing activities:
Common stock dividends	(49)	(46)
Capital contributions from parent	55	180
Proceeds from issuance of long-term debt	297	297
Net change in commercial paper and other short-term borrowings	(318)	(230)
Other	(9)	(10)
Net cash flows from (used for) financing activities	(24)	191
Net increase (decrease) in cash, cash equivalents and restricted cash	4	81
Cash, cash equivalents and restricted cash at beginning of period	7	5
Cash, cash equivalents and restricted cash at end of period	11	86
Supplemental cash flows information:
Interest	(40)	(40)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 91	$ 152

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2024
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684 Derivatives - Refer to Note 1 0 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486
IPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684 Derivatives - Refer to Note 1 0 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486
WPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684 Derivatives - Refer to Note 1 0 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486

Property, Plant and Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2024
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of March 31, 2024 given construction costs were reasonably and prudently incurred.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of March 31, 2024 given construction costs were reasonably and prudently incurred.

Receivables

Receivables	3 Months Ended
	Mar. 31, 2024
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (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. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of March 31, 2024, IPL had $92 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 for the three months ended March 31 were as follows (in millions): 2024 2023 Maximum outstanding aggregate cash proceeds $79 $89 Average outstanding aggregate cash proceeds 24 58 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2024 December 31, 2023 Customer accounts receivable $125 $130 Unbilled utility revenues 89 98 Other receivables 1 1 Receivables sold to third party 215 229 Less: cash proceeds 18 1 Deferred proceeds 197 228 Less: allowance for expected credit losses 13 12 Fair value of deferred proceeds $184 $216 As of March 31, 2024, outstanding receivables past due under the Receivables Agreement were $22 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2024 2023 Collections $557 $591 Write-offs, net of recoveries 3 2 Effective April 2024, the limit on cash proceeds under the Receivables Agreement is $80 million.
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (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. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of March 31, 2024, IPL had $92 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 for the three months ended March 31 were as follows (in millions): 2024 2023 Maximum outstanding aggregate cash proceeds $79 $89 Average outstanding aggregate cash proceeds 24 58 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2024 December 31, 2023 Customer accounts receivable $125 $130 Unbilled utility revenues 89 98 Other receivables 1 1 Receivables sold to third party 215 229 Less: cash proceeds 18 1 Deferred proceeds 197 228 Less: allowance for expected credit losses 13 12 Fair value of deferred proceeds $184 $216 As of March 31, 2024, outstanding receivables past due under the Receivables Agreement were $22 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2024 2023 Collections $557 $591 Write-offs, net of recoveries 3 2 Effective April 2024, the limit on cash proceeds under the Receivables Agreement is $80 million.

Investments

Investments	3 Months Ended
	Mar. 31, 2024
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions): 2024 2023 ATC Holdings ($12) ($13) Other (3) (4) ($15) ($17)

Common Equity

Common Equity	3 Months Ended
	Mar. 31, 2024
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 127,917 Equity-based compensation plans 154,267 Shares outstanding, March 31, 2024 256,379,032 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713
IPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 127,917 Equity-based compensation plans 154,267 Shares outstanding, March 31, 2024 256,379,032 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713
WPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 127,917 Equity-based compensation plans 154,267 Shares outstanding, March 31, 2024 256,379,032 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713

Debt

Debt	3 Months Ended
	Mar. 31, 2024
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of March 31, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated term loan credit agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be allocated or disbursed for the development and acquisition of WPL’s solar EGUs. Convertible Senior Notes - As of March 31, 2024, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (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 March 31, 2024, the net carrying amount of the Notes was $569 million, with unamortized debt issuance costs of $6 million, and the estimated fair value (Level 2) of the Notes was $567 million. As of March 31, 2024, 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.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8%
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of March 31, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated term loan credit agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be allocated or disbursed for the development and acquisition of WPL’s solar EGUs.

Revenues

Revenues	3 Months Ended
	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2024
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12% Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12% Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12% Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214

Benefit Plans

Benefit Plans	3 Months Ended
	Mar. 31, 2024
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — — As of March 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40 As of March 31, 2024, 242,680 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — — As of March 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40 As of March 31, 2024, 242,680 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — — As of March 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40 As of March 31, 2024, 242,680 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Derivative Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2024
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39 During the three months ended March 31, 2024, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of FTRs, natural gas and electricity contracts, and lower natural gas prices. 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. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At March 31, 2024 and December 31, 2023, 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. 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. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 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 - The interest rate derivative associated with AEF’s interest rate swap maturing in January 2026 was valued based on quoted prices that utilize current market interest rate forecasts. As of March 31, 2024 , $3 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 March 31, 2024, accumulated other comprehensive income included $2 million of income related to the interest rate swap. For the three months ended March 31, 2024 and 2023 , $1 million and $1 million , respectively, of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39 During the three months ended March 31, 2024, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of FTRs, natural gas and electricity contracts, and lower natural gas prices. 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. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At March 31, 2024 and December 31, 2023, 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. 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. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 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.
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39 During the three months ended March 31, 2024, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of FTRs, natural gas and electricity contracts, and lower natural gas prices. 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. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At March 31, 2024 and December 31, 2023, 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. 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. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 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.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s and WPL’s expansion of solar generation, and IPL’s repowering of the existing Franklin County wind farm. At March 31, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $191 million, $80 million and $111 million, respectively. NOTE 13(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 March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. 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 and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2024 and December 31, 2023. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $51 million as of March 31, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. 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 March 31, 2024 and December 31, 2023. 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 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. 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 March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. 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 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. 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 13(f) Collective Bargaining Agreements - At March 31, 2024, employees covered by collective bargaining agreements represented 53%, 70% 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.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s and WPL’s expansion of solar generation, and IPL’s repowering of the existing Franklin County wind farm. At March 31, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $191 million, $80 million and $111 million, respectively. NOTE 13(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 March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. 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 and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2024 and December 31, 2023. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $51 million as of March 31, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. 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 March 31, 2024 and December 31, 2023. 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 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. 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 March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. 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 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. 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 13(f) Collective Bargaining Agreements - At March 31, 2024, employees covered by collective bargaining agreements represented 53%, 70% 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.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s and WPL’s expansion of solar generation, and IPL’s repowering of the existing Franklin County wind farm. At March 31, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $191 million, $80 million and $111 million, respectively. NOTE 13(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 March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. 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 and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2024 and December 31, 2023. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $51 million as of March 31, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. 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 March 31, 2024 and December 31, 2023. 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 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. 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 March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. 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 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. 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 13(f) Collective Bargaining Agreements - At March 31, 2024, employees covered by collective bargaining agreements represented 53%, 70% 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.

Segments Of Business

Segments Of Business	3 Months Ended
	Mar. 31, 2024
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 2024
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2024 2023 ATC billings to WPL $37 $34 WPL billings to ATC 3 6 WPL owed ATC net amounts of $10 million as of March 31, 2024 and $10 million as of December 31, 2023.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2024 2023 ATC billings to WPL $37 $34 WPL billings to ATC 3 6 WPL owed ATC net amounts of $10 million as of March 31, 2024 and $10 million as of December 31, 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net income	$ 158	$ 163

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	3 Months Ended
	Mar. 31, 2024
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2024
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $939 $934 $839 $831 $100 $103 Pension and OPEB costs 340 347 168 171 172 176 Assets retired early 267 273 253 259 14 14 Asset retirement obligations (AROs) 200 194 165 160 35 34 Commodity cost recovery 100 120 5 12 95 108 Derivatives 97 102 33 34 64 68 WPL’s Western Wisconsin gas distribution expansion investments 44 44 — — 44 44 IPL’s Duane Arnold Energy Center PPA amendment 36 42 36 42 — — Other 197 205 68 68 129 137 $2,220 $2,261 $1,567 $1,577 $653 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $563 $566 $297 $299 $266 $267 Cost of removal obligations 380 366 241 242 139 124 Derivatives 49 65 28 34 21 31 Commodity cost recovery 61 48 25 13 36 35 Other 83 85 57 56 26 29 $1,136 $1,130 $648 $644 $488 $486

Receivables (Tables)

Receivables (Tables)	3 Months Ended
	Mar. 31, 2024
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions): 2024 2023 Maximum outstanding aggregate cash proceeds $79 $89 Average outstanding aggregate cash proceeds 24 58
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2024 December 31, 2023 Customer accounts receivable $125 $130 Unbilled utility revenues 89 98 Other receivables 1 1 Receivables sold to third party 215 229 Less: cash proceeds 18 1 Deferred proceeds 197 228 Less: allowance for expected credit losses 13 12 Fair value of deferred proceeds $184 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2024 2023 Collections $557 $591 Write-offs, net of recoveries 3 2
IPL [Member]
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions): 2024 2023 Maximum outstanding aggregate cash proceeds $79 $89 Average outstanding aggregate cash proceeds 24 58
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2024 December 31, 2023 Customer accounts receivable $125 $130 Unbilled utility revenues 89 98 Other receivables 1 1 Receivables sold to third party 215 229 Less: cash proceeds 18 1 Deferred proceeds 197 228 Less: allowance for expected credit losses 13 12 Fair value of deferred proceeds $184 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2024 2023 Collections $557 $591 Write-offs, net of recoveries 3 2

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2024
Schedule of Equity Method Investments [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions): 2024 2023 ATC Holdings ($12) ($13) Other (3) (4) ($15) ($17)

Common Equity (Tables)

Common Equity (Tables)	3 Months Ended
	Mar. 31, 2024
Schedule of Capitalization, Equity [Line Items]
Common Share Activity	A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 127,917 Equity-based compensation plans 154,267 Shares outstanding, March 31, 2024 256,379,032
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713
IPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713
WPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 158 158 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) 1 (2) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 163 163 Common stock dividends ($0.4525 per share) (113) (113) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other (3) (3) Other comprehensive loss, net of tax (1) (1) Ending balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 63 63 Common stock dividends (50) (50) Capital contributions from parent 50 50 Ending balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 72 72 Common stock dividends (70) (70) Ending balance, March 31, 2023 $33 $2,807 $970 $3,810 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 92 92 Common stock dividends (49) (49) Capital contributions from parent 55 55 Ending balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Three Months Ended March 31, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 88 88 Common stock dividends (46) (46) Capital contributions from parent 180 180 Ending balance, March 31, 2023 $66 $2,413 $1,234 $3,713

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2024
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2024 Alliant Energy IPL WPL Amount outstanding $334 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $666 $200 $300 Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $14 $— $390 $349 Average amount outstanding (based on daily outstanding balances) $487 $574 $1 $— $255 $304 Weighted average interest rates 5.5% 4.8% 5.5% —% 5.5% 4.8%

Revenues (Tables)

Revenues (Tables)	3 Months Ended
	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $297 $285 $150 $143 $147 $142 Retail - commercial 186 185 114 112 72 73 Retail - industrial 223 216 112 107 111 109 Wholesale 47 46 13 12 34 34 Bulk power and other 38 36 3 14 35 22 Total Electric Utility 791 768 392 388 399 380 Gas Utility: Retail - residential 126 167 68 93 58 74 Retail - commercial 61 88 30 44 31 44 Retail - industrial 5 7 3 4 2 3 Transportation/other 13 14 7 9 6 5 Total Gas Utility 205 276 108 150 97 126 Other Utility: Steam 12 10 12 10 — — Other utility 1 1 1 1 — — Total Other Utility 13 11 13 11 — — Non-Utility and Other: Travero and other 22 22 — — — — Total Non-Utility and Other 22 22 — — — — Total revenues $1,031 $1,077 $513 $549 $496 $506

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2024
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12%
Summary Of Tax Credit Carryforwards	At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12%
Summary Of Tax Credit Carryforwards	At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Overall income tax rate (7%) (1%) (19%) (18%) 6% 12%
Summary Of Tax Credit Carryforwards	At March 31, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $403 $6 $1 Federal tax credits 2032-2044 685 462 214

Benefit Plans (Tables)

Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2024
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Alliant Energy 2024 2023 2024 2023 Service cost $1 $1 $— $1 Interest cost 11 11 2 2 Expected return on plan assets (13) (13) (1) (1) Amortization of actuarial loss 6 7 — — $5 $6 $1 $2 Defined Benefit Pension Plans OPEB Plans IPL 2024 2023 2024 2023 Service cost $1 $1 $— $— Interest cost 5 5 1 1 Expected return on plan assets (7) (7) (1) (1) Amortization of actuarial loss 2 3 — — $1 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2024 2023 2024 2023 Interest cost $5 $5 $1 $1 Expected return on plan assets (6) (5) — — Amortization of actuarial loss 3 3 — — $2 $3 $1 $1
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2024 2023 2024 2023 2024 2023 Compensation expense $4 $3 $2 $2 $2 $1 Income tax benefits 1 1 1 — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 123,098 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 140,683 48.40 Restricted stock units 120,557 48.40

Derivative Instruments (Tables)

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39
Balance Sheet Offsetting	However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39
Balance Sheet Offsetting	However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2024, 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 MWhs Years MWhs Years Dths Years Alliant Energy 1,412 2024-2026 4,162 2024 173,746 2024-2032 IPL 673 2024-2026 1,444 2024 78,790 2024-2030 WPL 739 2024-2026 2,718 2024 94,956 2024-2032
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $16 $44 $12 $30 $4 $14 Non-current derivative assets 40 44 22 24 18 20 Current derivative liabilities 49 51 23 22 26 29 Non-current derivative liabilities 45 47 7 8 38 39
Balance Sheet Offsetting	However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net March 31, 2024 Derivative assets $56 $26 $34 $17 $22 $9 Derivative liabilities 94 64 30 13 64 51 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5
IPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5
WPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $10 $10 $— $— $10 $45 $45 $— $— $45 Commodity derivatives 56 — 46 10 56 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 94 — 91 3 94 98 — 93 5 98 Long-term debt (incl. current maturities) 9,333 — 9,051 — 9,051 9,034 — 8,677 — 8,677 IPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $6 $6 $— $— $6 $45 $45 $— $— $45 Commodity derivatives 34 — 26 8 34 54 — 30 24 54 Deferred proceeds 184 — — 184 184 216 — — 216 216 Liabilities: Commodity derivatives 30 — 27 3 30 30 — 25 5 30 Long-term debt (incl. current maturities) 3,945 — 3,607 — 3,607 3,945 — 3,664 — 3,664 WPL March 31, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $22 $— $20 $2 $22 $34 $— $29 $5 $34 Liabilities: Commodity derivatives 64 — 64 — 64 68 — 68 — 68 Long-term debt 3,367 — 3,176 — 3,176 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (3) (4) — — Settlements (a) (14) (20) (32) (32) Ending balance, March 31 $7 ($5) $184 $153 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($3) ($4) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (4) 1 — — Settlements (a) (10) (17) (32) (32) Ending balance, March 31 $5 $— $184 $153 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 March 31 ($4) $1 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) 1 (5) Settlements (4) (3) Ending balance, March 31 $2 ($5) 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 March 31 $1 ($5) (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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2024 ($1) $8 ($1) $6 $— $2 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies (

Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2024, 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 IPL WPL Natural gas $807 $335 $472 Coal 167 110 57 Other (a) 124 52 25 $1,098 $497 $554 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2024, 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): Alliant Energy IPL WPL Range of estimated future costs $8 - $29 $6 - $18 $2 - $11 Current and non-current environmental liabilities $13 $8 $5

Segments Of Business (Tables)

Segments Of Business (Tables)	3 Months Ended
	Mar. 31, 2024
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2024 Revenues $791 $205 $13 $1,009 $22 $1,031 Operating income 164 47 5 216 6 222 Net income attributable to Alliant Energy common shareowners 155 3 158 Three Months Ended March 31, 2023 Revenues $768 $276 $11 $1,055 $22 $1,077 Operating income 163 50 4 217 5 222 Net income attributable to Alliant Energy common shareowners 160 3 163 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $392 $108 $13 $513 Operating income 57 22 6 85 Net income 63 Three Months Ended March 31, 2023 Revenues $388 $150 $11 $549 Operating income 66 27 3 96 Net income 72 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2024 Revenues $399 $97 $— $496 Operating income (loss) 107 25 (1) 131 Net income 92 Three Months Ended March 31, 2023 Revenues $380 $126 $— $506 Operating income 97 23 1 121 Net income 88

Related Parties (Tables)

Related Parties (Tables)	3 Months Ended
	Mar. 31, 2024
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2024 2023 ATC billings to WPL $37 $34 WPL billings to ATC 3 6
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2024 2023 2024 2023 Corporate Services billings $43 $40 $40 $36 Sales credited — 7 22 13 Purchases billed 96 93 7 15
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2024 December 31, 2023 March 31, 2024 December 31, 2023 Net payables to Corporate Services $132 $129 $70 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2024 2023 ATC billings to WPL $37 $34 WPL billings to ATC 3 6

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Regulatory assets	$ 2,220	$ 2,261
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	939	934
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	340	347
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	267	273
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	200	194
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	100	120
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	97	102
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	44	44
IPL's Duane Arnold Energy Center PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	36	42
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	197	205
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,567	1,577
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	839	831
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	168	171
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	253	259
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	165	160
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	5	12
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	33	34
IPL [Member] | IPL's Duane Arnold Energy Center PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	36	42
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	68	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	653	684
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	100	103
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	172	176
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	14	14
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	35	34
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	95	108
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	64	68
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	44	44
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 129	$ 137

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,136	$ 1,130
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	563	566
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	380	366
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	49	65
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	61	48
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	83	85
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	648	644
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	297	299
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	241	242
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	28	34
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	13
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	57	56
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	488	486
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	266	267
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	139	124
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21	31
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36	35
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 26	$ 29

Property, Plant and Equipment (

Property, Plant and Equipment (Narrative) (Details) - WPL [Member] $ in Millions	Mar. 31, 2024 USD ($) MW
Property, Plant and Equipment [Line Items]
Electric Capacity of Solar Project | MW	1,100
Construction Project Cost Target Exceedance | $	$ 180

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions	Apr. 30, 2024	Mar. 31, 2024
Receivables [Line Items]
Available capacity		$ 92
Subsequent Event [Member]
Receivables [Line Items]
Available capacity	$ 80
Financial Asset, Past Due [Member]
Receivables [Line Items]
Outstanding receivables past due		$ 22

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Maximum [Member]
Receivables [Line Items]
Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 79	$ 89
Average [Member]
Receivables [Line Items]
Average outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 24	$ 58

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Receivables [Line Items]
Fair value of deferred proceeds	$ 184	$ 216
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	184	216
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	125	130
Unbilled utility revenues	89	98
Other receivables	1	1
Receivables sold to third party	215	229
Less: cash proceeds	18	1
Deferred proceeds	197	228
Less: allowance for expected credit losses	13	12
Fair value of deferred proceeds	$ 184	$ 216

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Receivables [Line Items]
Collections	$ 557	$ 591
Write-offs, net of recoveries	$ 3	$ 2

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (15)	$ (17)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(12)	(13)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(3)	(4)
Total [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (15)	$ (17)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	3 Months Ended
	Mar. 31, 2024 shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2024 (in shares)	256,096,848
Shareowner Direct Plan (in shares)	127,917
Equity-based compensation plans (in shares)	154,267
Shares outstanding, March 31, 2024 (in shares)	256,379,032

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 6,777
Beginning balance	6,777	$ 6,276
Net income attributable to common shareowners	158	163
Net income	158	163
Common stock dividends	(123)	(113)
Shareowner Direct Plan issuances	6	6
Equity-based compensation plans and other	(2)	(3)
Other comprehensive income (loss), net of tax	1	(1)
Ending balance	6,817
Ending balance	$ 6,817	$ 6,328
Common stock dividends (in dollars per share)	$ 0.48	$ 0.4525
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 3
Ending balance	3	3
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,030	2,777
Shareowner Direct Plan issuances	6	6
Equity-based compensation plans and other	(3)	(3)
Ending balance	3,033	2,780
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,756	3,509
Net income attributable to common shareowners	158	163
Common stock dividends	(123)	(113)
Ending balance	3,791	3,559
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1	0
Other comprehensive income (loss), net of tax	1	(1)
Ending balance	2	(1)
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(13)	(13)
Equity-based compensation plans and other	1
Ending balance	(12)	(13)
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,974
Beginning balance	3,974	3,808
Net income	63	72
Common stock dividends	(50)	(70)
Capital contributions from parent	50	0
Ending balance	4,037
Ending balance	4,037	3,810
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33
Ending balance	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,887	2,807
Capital contributions from parent	50
Ending balance	2,937	2,807
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,054	968
Net income	63	72
Common stock dividends	(50)	(70)
Ending balance	1,067	970
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,897
Beginning balance	3,897	3,491
Net income	92	88
Common stock dividends	(49)	(46)
Capital contributions from parent	55	180
Ending balance	3,995
Ending balance	3,995	3,713
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66
Ending balance	66	66
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,478	2,233
Capital contributions from parent	55	180
Ending balance	2,533	2,413
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,353	1,192
Net income	92	88
Common stock dividends	(49)	(46)
Ending balance	$ 1,396	$ 1,234

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2025	Dec. 31, 2023
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Payments to retire long-term debt	300	$ 0
Long-term debt, fair value	9,051			$ 8,677
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	500
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	200
Long-term debt, fair value	3,607			3,664
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	300
Long-term debt, fair value	3,176			$ 2,933
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	6%
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member] | Forecast [Member]
Debt [Line Items]
Long-term debt			$ 100
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2024 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Payments to retire long-term debt	$ 300
Debentures [Member] | 5.375% debenture, due 2034 [Member] | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	5.375%
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member]
Debt [Line Items]
Long-term debt, carrying value	$ 569
Unamortized debt issuance costs	6
Long-term debt, fair value	$ 567
Shares included in diluted earnings per share (in shares)	0

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Mar. 31, 2024 USD ($)
Debt [Line Items]
Amount outstanding	$ 334
Weighted average interest rates	5.50%
Available credit facility capacity	$ 666
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0%
Available credit facility capacity	$ 200
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0%
Available credit facility capacity	$ 300

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 632	$ 793
Average amount outstanding (based on daily outstanding balances)	$ 487	$ 574
Weighted average interest rates	5.50%	4.80%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 14	$ 0
Average amount outstanding (based on daily outstanding balances)	$ 1	$ 0
Weighted average interest rates	5.50%	0%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 390	$ 349
Average amount outstanding (based on daily outstanding balances)	$ 255	$ 304
Weighted average interest rates	5.50%	4.80%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,031	$ 1,077
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	791	768
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	297	285
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	186	185
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	223	216
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	46
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	38	36
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	205	276
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	126	167
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61	88
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	7
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	11
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	10
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	22
Non-utility and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	22
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	513	549
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	392	388
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	150	143
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	114	112
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	112	107
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	12
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	14
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	108	150
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	68	93
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	44
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	4
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	9
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	11
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	10
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	496	506
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	399	380
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	147	142
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72	73
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	111	109
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34	34
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	35	22
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	97	126
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	58	74
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31	44
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	5
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Effective Tax Rate [Line Items]
Overall income tax rate	(7.00%)	(1.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(19.00%)	(18.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	6%	12%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2024 USD ($)
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 403
Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	685
IPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	6
IPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	462
WPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
WPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	$ 214

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 22
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 11
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 10
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	242,680

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1
Interest cost	11	11
Expected return on plan assets	(13)	(13)
Amortization of actuarial loss	6	7
Total	5	6
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1
Interest cost	2	2
Expected return on plan assets	(1)	(1)
Amortization of actuarial loss	0	0
Total	1	2
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	5	5
Expected return on plan assets	(7)	(7)
Amortization of actuarial loss	2	3
Total	1	2
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	(1)	(1)
Amortization of actuarial loss	0	0
Total	0	0
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	5	5
Expected return on plan assets	(6)	(5)
Amortization of actuarial loss	3	3
Total	2	3
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Expected return on plan assets	0	0
Amortization of actuarial loss	0	0
Total	$ 1	$ 1

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Compensation expense	$ 4	$ 3
Income tax benefits	1	1
IPL [Member]
Compensation expense	2	2
Income tax benefits	1	0
WPL [Member]
Compensation expense	2	1
Income tax benefits	$ 0	$ 0

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Performance Shares (total shareowner return metric) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	123,098
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 46.04
Performance Shares (net income and diversity metric) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	140,683
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.40
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	120,557
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.40

Derivative Instruments (Narrati

Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Derivative Instruments [Line Items]
Non-current interest rate derivative assets	$ 173		$ 177
Accumulated other comprehensive income, interest rate swap	2		$ 1
Interest expense, interest rate swap	107	$ 94
Alliant Energy Finance LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Non-current interest rate derivative assets	3
Accumulated other comprehensive income, interest rate swap	2
Interest expense, interest rate swap	$ 1	$ 1

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member]	3 Months Ended
	Mar. 31, 2024 Dekatherms MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,412
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	673
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	739
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	4,162
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,444
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	2,718
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	173,746
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	78,790
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	94,956

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 16	$ 44
Non-current derivative assets	40	44
Current derivative liabilities	49	51
Non-current derivative liabilities	45	47
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	12	30
Non-current derivative assets	22	24
Current derivative liabilities	23	22
Non-current derivative liabilities	7	8
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	4	14
Non-current derivative assets	18	20
Current derivative liabilities	26	29
Non-current derivative liabilities	$ 38	$ 39

Derivative Instruments (Balance

Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$ 56	$ 88
Derivative assets, Net	26	47
Derivative liabilities, Gross (as reported)	94	98
Derivative liabilities, Net	64	57
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	34	54
Derivative assets, Net	17	32
Derivative liabilities, Gross (as reported)	30	30
Derivative liabilities, Net	13	8
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	22	34
Derivative assets, Net	9	15
Derivative liabilities, Gross (as reported)	64	68
Derivative liabilities, Net	$ 51	$ 49

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Carrying Amount [Member]
Assets:
Money market fund investments	$ 10	$ 45
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	9,333	9,034
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	6	45
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	3,945	3,945
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	3,367	3,070
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	56	88
Liabilities:
Derivatives	94	98
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	54
Liabilities:
Derivatives	30	30
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	22	34
Liabilities:
Derivatives	64	68
Carrying Amount [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Money market fund investments	10	45
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	9,051	8,677
IPL [Member]
Assets:
Money market fund investments	6	45
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	3,607	3,664
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	3,176	2,933
Commodity Contracts [Member]
Assets:
Derivatives	56	88
Liabilities:
Derivatives	94	98
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	54
Liabilities:
Derivatives	30	30
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	22	34
Liabilities:
Derivatives	64	68
Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Level 1 [Member]
Assets:
Money market fund investments	10	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	6	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	0
Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	9,051	8,677
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,607	3,664
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	3,176	2,933
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	46	59
Liabilities:
Derivatives	91	93
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	26	30
Liabilities:
Derivatives	27	25
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	20	29
Liabilities:
Derivatives	64	68
Level 2 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	184	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	10	29
Liabilities:
Derivatives	3	5
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	8	24
Liabilities:
Derivatives	3	5
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	2	5
Liabilities:
Derivatives	0	0
Level 3 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	$ 0	$ 0

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 24	$ 19
Total net gains (losses) included in changes in net assets (realized/unrealized)	(3)	(4)
Settlements	(14)	(20)
Ending balance	7	(5)
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 March 31	(3)	(4)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	19	16
Total net gains (losses) included in changes in net assets (realized/unrealized)	(4)	1
Settlements	(10)	(17)
Ending balance	5	0
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 March 31	(4)	1
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5	3
Total net gains (losses) included in changes in net assets (realized/unrealized)	1	(5)
Settlements	(4)	(3)
Ending balance	2	(5)
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 March 31	1	(5)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Settlements	(32)	(32)
Ending balance	184	153
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 March 31	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Settlements	(32)	(32)
Ending balance	184	153
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 March 31	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 7	$ 24	$ (5)	$ 19
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets		3
Fair value, net derivative liabilities	(1)
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	8	21
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	5	19	0	16
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets		3
Fair value, net derivative liabilities	(1)
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	6	16
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	2	5	$ (5)	$ 3
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	0	0
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 2	$ 5

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,098
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	497
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	554
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	191
Capital Purchase Commitment [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	80
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	111
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	51
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	17
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Indemnifications, renewable tax credit transfers	76
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Indemnifications, renewable tax credit transfers	$ 22
Workforce Subject to Collective Bargaining Arrangements [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement, percentage	53%
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement, percentage	70%
Workforce Subject to Collective Bargaining Arrangements [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement, percentage	83%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement, percentage	18%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement, percentage	53%
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent	6%
Obligations, maximum	$ 49
Federal Energy Regulatory Commission [Member]
Commitments and Contingencies [Line Items]
MISO base return on equity, percentage		10.02%	9.88%

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,098
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	497
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	554
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	807
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	335
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	472
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	167
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	110
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	57
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	124
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	52
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 25

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 13
IPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	8
WPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	5
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	8
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	6
Minimum [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	2
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	29
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	18
Maximum [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 11

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,031	$ 1,077
Operating income (loss)	222	222
Net income (loss) attributable to common shareowners	158	163
Net income	158	163
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	513	549
Operating income (loss)	85	96
Net income	63	72
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	496	506
Operating income (loss)	131	121
Net income	92	88
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	791	768
Operating income (loss)	164	163
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	392	388
Operating income (loss)	57	66
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	399	380
Operating income (loss)	107	97
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	205	276
Operating income (loss)	47	50
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	108	150
Operating income (loss)	22	27
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	97	126
Operating income (loss)	25	23
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	13	11
Operating income (loss)	5	4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	13	11
Operating income (loss)	6	3
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Operating income (loss)	(1)	1
Non-utility and Other [Member]
Segment Reporting Information [Line Items]
Revenues	22	22
Operating income (loss)	6	5
Net income (loss) attributable to common shareowners	3	3
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	1,009	1,055
Operating income (loss)	216	217
Net income (loss) attributable to common shareowners	$ 155	$ 160

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
WPL [Member] | WPL Owed ATC LLC [Member] | Related Party [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 10	$ 10

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 43	$ 40
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	40	36
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	0	7
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	22	13
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	96	93
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 7	$ 15

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Related Party [Member] - Corporate Services [Member] - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 132	$ 129
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 70	$ 72

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - WPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 37	$ 34
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 3	$ 6