Alliant Energy (LNT) 10-Q 2 Aug 24 2024 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	6 Months Ended
	Jun. 30, 2024 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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	256,499,575
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues:
Electric utility	$ 789	$ 799	$ 1,580	$ 1,567
Gas utility	69	77	273	353
Other utility	10	13	24	25
Non-utility	26	23	48	45
Total revenues	894	912	1,925	1,990
Operating expenses:
Electric production fuel and purchased power	138	166	301	322
Electric transmission service	147	138	300	284
Cost of gas sold	25	33	139	215
Asset valuation charge for IPL's Lansing Generating Station	60	0	60	0
Other operation and maintenance	177	163	336	338
Depreciation and amortization	188	167	376	333
Taxes other than income taxes	29	28	61	59
Total operating expenses	764	695	1,573	1,551
Operating income	130	217	352	439
Other (income) and deductions:
Interest expense	108	96	215	190
Equity income from unconsolidated investments, net	(15)	(14)	(31)	(31)
Allowance for funds used during construction	(19)	(24)	(38)	(43)
Other	2	(1)	4	2
Total other (income) and deductions	76	57	150	118
Income (loss) before income taxes	54	160	202	321
Income tax expense (benefit)	(33)	0	(43)	(2)
Net income attributable to common shareowners	$ 87	$ 160	$ 245	$ 323
Weighted average number of common shares outstanding:
Basic (in shares)	256,400	251,700	256,300	251,400
Diluted (in shares)	256,700	251,900	256,600	251,600
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.34	$ 0.64	$ 0.96	$ 1.28
Diluted (in dollars per share)	$ 0.34	$ 0.64	$ 0.95	$ 1.28
IPL [Member]
Revenues:
Electric utility	$ 404	$ 431	$ 795	$ 819
Gas utility	40	44	148	194
Other utility	9	12	23	24
Total revenues	453	487	966	1,037
Operating expenses:
Electric production fuel and purchased power	48	66	116	113
Electric transmission service	99	96	202	201
Cost of gas sold	17	20	77	116
Asset valuation charge for IPL's Lansing Generating Station	60	0	60	0
Other operation and maintenance	102	85	187	181
Depreciation and amortization	97	96	193	191
Taxes other than income taxes	14	14	30	29
Total operating expenses	437	377	865	831
Operating income	16	110	101	206
Other (income) and deductions:
Interest expense	42	37	84	74
Allowance for funds used during construction	(11)	(4)	(21)	(8)
Other	0	1	0	3
Total other (income) and deductions	31	34	63	69
Income (loss) before income taxes	(15)	76	38	137
Income tax expense (benefit)	(33)	(13)	(43)	(24)
Net income attributable to common shareowners	18	89	81	161
WPL [Member]
Revenues:
Electric utility	385	368	785	748
Gas utility	29	33	125	159
Other utility	1	1	1	1
Total revenues	415	402	911	908
Operating expenses:
Electric production fuel and purchased power	90	99	186	209
Electric transmission service	49	42	98	83
Cost of gas sold	8	13	62	99
Other operation and maintenance	67	67	128	133
Depreciation and amortization	87	69	178	137
Taxes other than income taxes	14	13	28	27
Total operating expenses	315	303	680	688
Operating income	100	99	231	220
Other (income) and deductions:
Interest expense	41	36	82	72
Allowance for funds used during construction	(8)	(19)	(17)	(35)
Other	0	(4)	2	(3)
Total other (income) and deductions	33	13	67	34
Income (loss) before income taxes	67	86	164	186
Income tax expense (benefit)	3	14	8	26
Net income attributable to common shareowners	$ 64	$ 72	$ 156	$ 160

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 92	$ 62
Accounts receivable, less allowance for expected credit losses	409	475
Production fuel, at weighted average cost	65	62
Gas stored underground, at weighted average cost	52	79
Materials and supplies, at weighted average cost	206	202
Regulatory assets	212	232
Other	178	160
Total current assets	1,214	1,272
Property, plant and equipment, net	17,706	17,157
Investments:
ATC Holdings	400	386
Other	223	216
Total investments	623	602
Other assets:
Regulatory assets	2,133	2,029
Deferred charges and other	160	177
Total other assets	2,293	2,206
Total assets	21,836	21,237
Current liabilities:
Current maturities of long-term debt	804	809
Commercial paper	52	475
Accounts payable	581	611
Regulatory liabilities	110	107
Other	307	302
Total current liabilities	1,854	2,304
Long-term debt, net (excluding current portion)	8,900	8,225
Other liabilities:
Deferred tax liabilities	2,086	2,042
Regulatory liabilities	1,026	1,023
Pension and other benefit obligations	240	249
Other	939	617
Total other liabilities	4,291	3,931
Commitments and contingencies (Note 14)
Common equity:
Common stock	3	3
Additional paid-in capital	3,042	3,030
Retained earnings	3,755	3,756
Accumulated other comprehensive income	3	1
Shares in deferred compensation trust - 352,514 and 379,006 shares at a weighted average cost of $35.38 and $34.48 per share	(12)	(13)
Total common equity	6,791	6,777
Total liabilities and equity	21,836	21,237
IPL [Member]
Current assets:
Cash and cash equivalents	9	53
Accounts receivable, less allowance for expected credit losses	186	242
Production fuel, at weighted average cost	36	27
Gas stored underground, at weighted average cost	18	35
Materials and supplies, at weighted average cost	123	122
Regulatory assets	84	93
Other	68	51
Total current assets	524	623
Property, plant and equipment, net	8,670	8,298
Other assets:
Regulatory assets	1,464	1,484
Deferred charges and other	74	84
Total other assets	1,538	1,568
Total assets	10,732	10,489
Current liabilities:
Current maturities of long-term debt	500	500
Accounts payable	252	262
Accrued taxes	56	50
Accrued interest	39	40
Regulatory liabilities	62	72
Other	110	101
Total current liabilities	1,019	1,025
Long-term debt, net (excluding current portion)	3,446	3,445
Other liabilities:
Deferred tax liabilities	1,150	1,091
Regulatory liabilities	556	572
Pension and other benefit obligations	48	51
Other	433	331
Total other liabilities	2,187	2,045
Commitments and contingencies (Note 14)
Common equity:
Common stock	33	33
Additional paid-in capital	3,012	2,887
Retained earnings	1,035	1,054
Total common equity	4,080	3,974
Total liabilities and equity	10,732	10,489
WPL [Member]
Current assets:
Cash and cash equivalents	80	7
Accounts receivable, less allowance for expected credit losses	209	219
Production fuel, at weighted average cost	30	35
Gas stored underground, at weighted average cost	34	44
Materials and supplies, at weighted average cost	79	77
Regulatory assets	128	139
Prepaid gross receipts tax	49	49
Other	38	43
Total current assets	647	613
Property, plant and equipment, net	8,554	8,415
Other assets:
Regulatory assets	669	545
Deferred charges and other	55	61
Total other assets	724	606
Total assets	9,925	9,634
Current liabilities:
Commercial paper	0	318
Accounts payable	261	293
Accrued interest	46	40
Regulatory liabilities	48	35
Other	83	89
Total current liabilities	438	775
Long-term debt, net (excluding current portion)	3,368	3,070
Other liabilities:
Deferred tax liabilities	804	827
Regulatory liabilities	470	451
Pension and other benefit obligations	114	121
Other	721	493
Total other liabilities	2,109	1,892
Commitments and contingencies (Note 14)
Common equity:
Common stock	66	66
Additional paid-in capital	2,533	2,478
Retained earnings	1,411	1,353
Total common equity	4,010	3,897
Total liabilities and equity	$ 9,925	$ 9,634

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 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)	256,499,575	256,096,848
Shares in deferred compensation trust (in shares)	352,514	379,006
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 35.38	$ 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	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Cash flows from operating activities:
Net income	$ 245	$ 323
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	376	333
Deferred tax expense (benefit) and tax credits	(47)	0
Asset valuation charge for IPL's Lansing Generating Station	60	0
Other	(4)	(18)
Other changes in assets and liabilities:
Accounts receivable	(242)	(186)
Gas stored underground	27	63
Derivative assets	(17)	86
Regulatory assets	43	(36)
Accounts payable	75	(84)
Regulatory liabilities	(12)	(116)
Deferred income taxes	86	24
Other	(28)	(78)
Net cash flows from operating activities	562	311
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(870)	(758)
Other construction and acquisition expenditures	(90)	(62)
Cash receipts on sold receivables	306	272
Proceeds from sales of partial ownership interests in West Riverside	123	120
Other	(2)	(54)
Net cash flows from (used for) investing activities	(533)	(482)
Cash flows from (used for) financing activities:
Common stock dividends	(246)	(226)
Proceeds from issuance of common stock, net	12	76
Proceeds from issuance of long-term debt	969	862
Payments to retire long-term debt	(305)	(404)
Net change in commercial paper and other short-term borrowings	(423)	(146)
Other	(6)	(1)
Net cash flows from (used for) financing activities	1	161
Net increase (decrease) in cash, cash equivalents and restricted cash	30	(10)
Cash, cash equivalents and restricted cash at beginning of period	63	24
Cash, cash equivalents and restricted cash at end of period	93	14
Supplemental cash flows information:
Interest	(207)	(179)
Income taxes, net	89	3
Significant non-cash investing and financing activities:
Accrued capital expenditures	272	300
Beneficial interest obtained in exchange for securitized accounts receivable	171	175
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	99
IPL [Member]
Cash flows from operating activities:
Net income	81	161
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	193	191
Deferred tax expense (benefit) and tax credits	(35)	5
Asset valuation charge for IPL's Lansing Generating Station	60	0
Other	7	(3)
Other changes in assets and liabilities:
Accounts receivable	(251)	(216)
Gas stored underground	17	33
Derivative assets	(18)	43
Accounts payable	19	(32)
Regulatory liabilities	(16)	(78)
Deferred income taxes	92	8
Other	(2)	(60)
Net cash flows from operating activities	147	52
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(500)	(251)
Cash receipts on sold receivables	306	272
Other	(15)	(36)
Net cash flows from (used for) investing activities	(209)	(15)
Cash flows from (used for) financing activities:
Common stock dividends	(100)	(140)
Capital contributions from parent	125	40
Net change in commercial paper and other short-term borrowings	0	55
Other	(7)	2
Net cash flows from (used for) financing activities	18	(43)
Net increase (decrease) in cash, cash equivalents and restricted cash	(44)	(6)
Cash, cash equivalents and restricted cash at beginning of period	53	15
Cash, cash equivalents and restricted cash at end of period	9	9
Supplemental cash flows information:
Interest	(85)	(74)
Income taxes, net	92	25
Significant non-cash investing and financing activities:
Accrued capital expenditures	119	95
Beneficial interest obtained in exchange for securitized accounts receivable	171	175
IPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	71
WPL [Member]
Cash flows from operating activities:
Net income	156	160
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	178	137
Other	(24)	(30)
Other changes in assets and liabilities:
Accounts receivable	10	33
Gas stored underground	10	31
Derivative assets	3	47
Regulatory assets	44	(35)
Accounts payable	41	(54)
Regulatory liabilities	5	(38)
Other	(32)	17
Net cash flows from operating activities	391	268
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(370)	(507)
Proceeds from sales of partial ownership interests in West Riverside	123	120
Other	0	(15)
Net cash flows from (used for) investing activities	(247)	(402)
Cash flows from (used for) financing activities:
Common stock dividends	(98)	(92)
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)	(246)
Other	(7)	(7)
Net cash flows from (used for) financing activities	(71)	132
Net increase (decrease) in cash, cash equivalents and restricted cash	73	(2)
Cash, cash equivalents and restricted cash at beginning of period	7	5
Cash, cash equivalents and restricted cash at end of period	80	3
Supplemental cash flows information:
Interest	(76)	(69)
Income taxes, net	(10)	(42)
Significant non-cash investing and financing activities:
Accrued capital expenditures	146	$ 196
WPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	$ 28

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 30, 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 six months ended June 30, 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. NOTE 1(b) Cash and Cash Equivalents - At June 30, 2024, Alliant Energy’s and WPL’s cash and cash equivalents included $73 million and $72 million of money market fund investments, respectively, with an interest rate of 5%.
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 six months ended June 30, 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. NOTE 1(b) Cash and Cash Equivalents - At June 30, 2024, Alliant Energy’s and WPL’s cash and cash equivalents included $73 million and $72 million of money market fund investments, respectively, with an interest rate of 5%.
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 six months ended June 30, 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. NOTE 1(b) Cash and Cash Equivalents - At June 30, 2024, Alliant Energy’s and WPL’s cash and cash equivalents included $73 million and $72 million of money market fund investments, respectively, with an interest rate of 5%.

Regulatory Matters

Regulatory Matters	6 Months Ended
	Jun. 30, 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL is currently allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period filed with the IUC in October 2023 included a request for continued recovery of and a return on the remaining net book value of Lansing through 2037. In June 2024, IPL reached a partial non-unanimous settlement agreement with certain stakeholders, which is subject to IUC approval. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing. As a result, the return on the remaining net book value is no longer probable of recovery from IPL’s retail electric customers, and in the second quarter of 2024, a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. A decision from the IUC on the settlement agreement is currently expected in the third quarter of 2024, with final rates expected to be effective October 1, 2024. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the six months ended June 30, 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the six months ended June 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.
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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL is currently allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period filed with the IUC in October 2023 included a request for continued recovery of and a return on the remaining net book value of Lansing through 2037. In June 2024, IPL reached a partial non-unanimous settlement agreement with certain stakeholders, which is subject to IUC approval. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing. As a result, the return on the remaining net book value is no longer probable of recovery from IPL’s retail electric customers, and in the second quarter of 2024, a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. A decision from the IUC on the settlement agreement is currently expected in the third quarter of 2024, with final rates expected to be effective October 1, 2024. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the six months ended June 30, 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the six months ended June 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.
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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL is currently allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period filed with the IUC in October 2023 included a request for continued recovery of and a return on the remaining net book value of Lansing through 2037. In June 2024, IPL reached a partial non-unanimous settlement agreement with certain stakeholders, which is subject to IUC approval. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing. As a result, the return on the remaining net book value is no longer probable of recovery from IPL’s retail electric customers, and in the second quarter of 2024, a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. A decision from the IUC on the settlement agreement is currently expected in the third quarter of 2024, with final rates expected to be effective October 1, 2024. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the six months ended June 30, 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the six months ended June 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.

Property, Plant and Equipment

Property, Plant and Equipment	6 Months Ended
	Jun. 30, 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 $195 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 June 30, 2024 given construction costs were reasonably and prudently incurred. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of June 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $496 million) no longer meets the criteria to be considered probable of abandonment, and $806 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the six months ended June 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.
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 $195 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 June 30, 2024 given construction costs were reasonably and prudently incurred. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of June 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $496 million) no longer meets the criteria to be considered probable of abandonment, and $806 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the six months ended June 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.

Receivables

Receivables	6 Months Ended
	Jun. 30, 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. Effective May 2024, the limit on cash proceeds under the Receivables Agreement was changed to $110 million. As of June 30, 2024, IPL had $65 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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $110 $110 $110 $110 Average outstanding aggregate cash proceeds 73 101 48 79 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2024 December 31, 2023 Customer accounts receivable $131 $130 Unbilled utility revenues 94 98 Other receivables 2 1 Receivables sold to third party 227 229 Less: cash proceeds 45 1 Deferred proceeds 182 228 Less: allowance for expected credit losses 11 12 Fair value of deferred proceeds $171 $216 As of June 30, 2024, outstanding receivables past due under the Receivables Agreement were $16 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Collections $456 $514 $1,013 $1,104 Write-offs, net of recoveries 2 2 5 4 Effective July 2024, the limit on cash proceeds under the Receivables Agreement was changed to $60 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. Effective May 2024, the limit on cash proceeds under the Receivables Agreement was changed to $110 million. As of June 30, 2024, IPL had $65 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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $110 $110 $110 $110 Average outstanding aggregate cash proceeds 73 101 48 79 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2024 December 31, 2023 Customer accounts receivable $131 $130 Unbilled utility revenues 94 98 Other receivables 2 1 Receivables sold to third party 227 229 Less: cash proceeds 45 1 Deferred proceeds 182 228 Less: allowance for expected credit losses 11 12 Fair value of deferred proceeds $171 $216 As of June 30, 2024, outstanding receivables past due under the Receivables Agreement were $16 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Collections $456 $514 $1,013 $1,104 Write-offs, net of recoveries 2 2 5 4 Effective July 2024, the limit on cash proceeds under the Receivables Agreement was changed to $60 million.

Investments

Investments	6 Months Ended
	Jun. 30, 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 and six months ended June 30 was as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC Holdings ($13) ($12) ($25) ($25) Other (2) (2) (6) (6) ($15) ($14) ($31) ($31)

Common Equity

Common Equity	6 Months Ended
	Jun. 30, 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 248,460 Equity-based compensation plans 154,267 Shares outstanding, June 30, 2024 256,499,575 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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739
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 248,460 Equity-based compensation plans 154,267 Shares outstanding, June 30, 2024 256,499,575 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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739
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 248,460 Equity-based compensation plans 154,267 Shares outstanding, June 30, 2024 256,499,575 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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739

Debt

Debt	6 Months Ended
	Jun. 30, 2024
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 5.5% 4.8% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of June 30, 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 June 2024, AEF issued $375 million of 5.4% senior notes due 2027 (with Alliant Energy as guarantor). The net proceeds from this issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. 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 June 30, 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 June 30, 2024, the net carrying amount of the Notes was $570 million, with unamortized debt issuance costs of $5 million, and the estimated fair value (Level 2) of the Notes was $568 million. As of June 30, 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 June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 5.5% 4.8%
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 5.5% 4.8% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of June 30, 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 June 2024, AEF issued $375 million of 5.4% senior notes due 2027 (with Alliant Energy as guarantor). The net proceeds from this issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. 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	6 Months Ended
	Jun. 30, 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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908
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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908
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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2024
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216

Benefit Plans

Benefit Plans	6 Months Ended
	Jun. 30, 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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2 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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1 As of June 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $19 million, $9 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of June 30, 2024, 234,773 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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2 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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1 As of June 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $19 million, $9 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of June 30, 2024, 234,773 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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2 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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1 As of June 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $19 million, $9 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of June 30, 2024, 234,773 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	6 Months Ended
	Jun. 30, 2024
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2024
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 39 During the six months ended June 30, 2024, Alliant Energy’s and IPL’s derivative assets increased primarily due to new FTRs resulting from the annual FTR auction in the second quarter of 2024 operated by MISO. Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 June 30, 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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 June 30, 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 June 30, 2024, accumulated other comprehensive income included $3 million of income related to the interest rate swap. Reductions to interest expense of $1 million and $2 million for the three and six months ended June 30, 2024, respectively, and $1 million and $1 million for the three and six months ended June 30, 2023, respectively, 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 June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 39 During the six months ended June 30, 2024, Alliant Energy’s and IPL’s derivative assets increased primarily due to new FTRs resulting from the annual FTR auction in the second quarter of 2024 operated by MISO. Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 June 30, 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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 June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 39 During the six months ended June 30, 2024, Alliant Energy’s and IPL’s derivative assets increased primarily due to new FTRs resulting from the annual FTR auction in the second quarter of 2024 operated by MISO. Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 June 30, 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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	6 Months Ended
	Jun. 30, 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies

Commitments And Contingencies	6 Months Ended
	Jun. 30, 2024
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(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 repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At June 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $116 million, $38 million and $76 million, respectively. NOTE 14(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 June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. 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. In 2022, Whiting Petroleum completed a business combination with Oasis Petroleum Inc., resulting in Chord Energy Corporation. In May 2024, Chord Energy Corporation completed a business combination with Enerplus Corporation. These business combinations are not expected to affect the scope of the Whiting Petroleum affiliate’s partnership obligations or Alliant Energy’s related guarantees; however, such business combinations substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of June 30, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of June 30, 2024 and December 31, 2023. 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 June 30, 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 June 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, 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. As of June 30, 2024, IPL and WPL provided indemnifications associated with $147 million and $50 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers 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 14(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 June 30, 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, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(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 14(f) Collective Bargaining Agreements - At June 30, 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 54% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are currently unable to predict the outcome.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(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 repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At June 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $116 million, $38 million and $76 million, respectively. NOTE 14(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 June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. 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. In 2022, Whiting Petroleum completed a business combination with Oasis Petroleum Inc., resulting in Chord Energy Corporation. In May 2024, Chord Energy Corporation completed a business combination with Enerplus Corporation. These business combinations are not expected to affect the scope of the Whiting Petroleum affiliate’s partnership obligations or Alliant Energy’s related guarantees; however, such business combinations substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of June 30, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of June 30, 2024 and December 31, 2023. 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 June 30, 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 June 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, 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. As of June 30, 2024, IPL and WPL provided indemnifications associated with $147 million and $50 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers 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 14(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 June 30, 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, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(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 14(f) Collective Bargaining Agreements - At June 30, 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 54% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are currently unable to predict the outcome.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(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 repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At June 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $116 million, $38 million and $76 million, respectively. NOTE 14(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 June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. 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. In 2022, Whiting Petroleum completed a business combination with Oasis Petroleum Inc., resulting in Chord Energy Corporation. In May 2024, Chord Energy Corporation completed a business combination with Enerplus Corporation. These business combinations are not expected to affect the scope of the Whiting Petroleum affiliate’s partnership obligations or Alliant Energy’s related guarantees; however, such business combinations substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of June 30, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of June 30, 2024 and December 31, 2023. 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 June 30, 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 June 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, 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. As of June 30, 2024, IPL and WPL provided indemnifications associated with $147 million and $50 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers 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 14(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 June 30, 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, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(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 14(f) Collective Bargaining Agreements - At June 30, 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 54% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are currently unable to predict the outcome.

Segments Of Business

Segments Of Business	6 Months Ended
	Jun. 30, 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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160
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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160
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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160

Related Parties

Related Parties	6 Months Ended
	Jun. 30, 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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC billings to WPL $39 $44 $76 $78 WPL billings to ATC 4 5 7 11 WPL owed ATC net amounts of $11 million as of June 30, 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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC billings to WPL $39 $44 $76 $78 WPL billings to ATC 4 5 7 11 WPL owed ATC net amounts of $11 million as of June 30, 2024 and $10 million as of December 31, 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net income	$ 245	$ 323

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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 six months ended June 30, 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.
Cash and Cash Equivalents	At June 30, 2024, Alliant Energy’s and WPL’s cash and cash equivalents included $73 million and $72 million of money market fund investments, respectively, with an interest rate of 5%.
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 six months ended June 30, 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 six months ended June 30, 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.
Cash and Cash Equivalents	At June 30, 2024, Alliant Energy’s and WPL’s cash and cash equivalents included $73 million and $72 million of money market fund investments, respectively, with an interest rate of 5%.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	6 Months Ended
	Jun. 30, 2024
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $958 $934 $848 $831 $110 $103 AROs 408 194 218 160 190 34 Pension and OPEB costs 334 347 165 171 169 176 Assets retired early 197 273 184 259 13 14 Derivatives 95 102 33 34 62 68 Commodity cost recovery 89 120 2 12 87 108 WPL’s Western Wisconsin gas distribution expansion investments 43 44 — — 43 44 IPL’s Duane Arnold Energy Center PPA amendment 30 42 30 42 — — Other 191 205 68 68 123 137 $2,345 $2,261 $1,548 $1,577 $797 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $601 $566 $296 $299 $305 $267 Cost of removal obligations 374 366 232 242 142 124 Derivatives 50 65 30 34 20 31 Commodity cost recovery 51 48 16 13 35 35 Other 60 85 44 56 16 29 $1,136 $1,130 $618 $644 $518 $486

Receivables (Tables)

Receivables (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $110 $110 $110 $110 Average outstanding aggregate cash proceeds 73 101 48 79
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2024 December 31, 2023 Customer accounts receivable $131 $130 Unbilled utility revenues 94 98 Other receivables 2 1 Receivables sold to third party 227 229 Less: cash proceeds 45 1 Deferred proceeds 182 228 Less: allowance for expected credit losses 11 12 Fair value of deferred proceeds $171 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Collections $456 $514 $1,013 $1,104 Write-offs, net of recoveries 2 2 5 4
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 and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $110 $110 $110 $110 Average outstanding aggregate cash proceeds 73 101 48 79
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2024 December 31, 2023 Customer accounts receivable $131 $130 Unbilled utility revenues 94 98 Other receivables 2 1 Receivables sold to third party 227 229 Less: cash proceeds 45 1 Deferred proceeds 182 228 Less: allowance for expected credit losses 11 12 Fair value of deferred proceeds $171 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 Collections $456 $514 $1,013 $1,104 Write-offs, net of recoveries 2 2 5 4

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30 was as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC Holdings ($13) ($12) ($25) ($25) Other (2) (2) (6) (6) ($15) ($14) ($31) ($31)

Common Equity (Tables)

Common Equity (Tables)	6 Months Ended
	Jun. 30, 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 248,460 Equity-based compensation plans 154,267 Shares outstanding, June 30, 2024 256,499,575
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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739
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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739
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 June 30, 2024 Beginning balance, March 31, 2024 $3 $3,033 $3,791 $2 ($12) $6,817 Net income attributable to Alliant Energy common shareowners 87 87 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 3 3 Other comprehensive income, net of tax 1 1 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $3 $2,780 $3,559 ($1) ($13) $6,328 Net income attributable to Alliant Energy common shareowners 160 160 Common stock dividends ($0.4525 per share) (113) (113) At-the-market offering program and Shareowner Direct Plan issuances 70 70 Equity-based compensation plans and other 4 (1) 3 Other comprehensive income, net of tax 4 4 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income Trust Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 245 245 Common stock dividends ($0.96 per share) (246) (246) Shareowner Direct Plan issuances 12 12 Equity-based compensation plans and other 1 1 Other comprehensive income, net of tax 2 2 Ending balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 323 323 Common stock dividends ($0.905 per share) (226) (226) At-the-market offering program and Shareowner Direct Plan issuances 76 76 Equity-based compensation plans and other 1 (1) — Other comprehensive income, net of tax 3 3 Ending balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $33 $2,937 $1,067 $4,037 Net income 18 18 Common stock dividends (50) (50) Capital contributions from parent 75 75 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $33 $2,807 $970 $3,810 Net income 89 89 Common stock dividends (70) (70) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 81 81 Common stock dividends (100) (100) Capital contributions from parent 125 125 Ending balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 161 161 Common stock dividends (140) (140) Capital contributions from parent 40 40 Ending balance, June 30, 2023 $33 $2,847 $989 $3,869 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2024 Beginning balance, March 31, 2024 $66 $2,533 $1,396 $3,995 Net income 64 64 Common stock dividends (49) (49) Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Three Months Ended June 30, 2023 Beginning balance, March 31, 2023 $66 $2,413 $1,234 $3,713 Net income 72 72 Common stock dividends (46) (46) Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 156 156 Common stock dividends (98) (98) Capital contributions from parent 55 55 Ending balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Six Months Ended June 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 160 160 Common stock dividends (92) (92) Capital contributions from parent 180 180 Ending balance, June 30, 2023 $66 $2,413 $1,260 $3,739

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 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): June 30, 2024 Alliant Energy IPL WPL Amount outstanding $52 $— $— Weighted average interest rates 5.5% —% —% Available credit facility capacity $948 $250 $300 Alliant Energy IPL WPL Three Months Ended June 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $435 $391 $19 $70 $57 $91 Average amount outstanding (based on daily outstanding balances) $275 $88 $2 $6 $8 $18 Weighted average interest rates 5.5% 5.3% 5.5% 5.3% 5.4% 5.2% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $381 $330 $1 $3 $131 $160 Weighted average interest rates 5.5% 4.8% 5.5% 5.3% 5.5% 4.8%

Revenues (Tables)

Revenues (Tables)	6 Months Ended
	Jun. 30, 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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908
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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908
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 June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $291 $284 $151 $151 $140 $133 Retail - commercial 191 201 118 129 73 72 Retail - industrial 237 245 118 130 119 115 Wholesale 43 49 13 14 30 35 Bulk power and other 27 20 4 7 23 13 Total Electric Utility 789 799 404 431 385 368 Gas Utility: Retail - residential 38 42 22 24 16 18 Retail - commercial 19 22 11 12 8 10 Retail - industrial 2 3 1 2 1 1 Transportation/other 10 10 6 6 4 4 Total Gas Utility 69 77 40 44 29 33 Other Utility: Steam 9 11 9 11 — — Other utility 1 2 — 1 1 1 Total Other Utility 10 13 9 12 1 1 Non-Utility and Other: Travero and other 26 23 — — — — Total Non-Utility and Other 26 23 — — — — Total revenues $894 $912 $453 $487 $415 $402 Alliant Energy IPL WPL Six Months Ended June 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $588 $569 $301 $294 $287 $275 Retail - commercial 377 385 232 241 145 144 Retail - industrial 460 460 229 236 231 224 Wholesale 89 95 26 26 63 69 Bulk power and other 66 58 7 22 59 36 Total Electric Utility 1,580 1,567 795 819 785 748 Gas Utility: Retail - residential 165 210 90 117 75 93 Retail - commercial 80 110 41 56 39 54 Retail - industrial 6 9 4 6 2 3 Transportation/other 22 24 13 15 9 9 Total Gas Utility 273 353 148 194 125 159 Other Utility: Steam 20 22 20 22 — — Other utility 4 3 3 2 1 1 Total Other Utility 24 25 23 24 1 1 Non-Utility and Other: Travero and other 48 45 — — — — Total Non-Utility and Other 48 45 — — — — Total revenues $1,925 $1,990 $966 $1,037 $911 $908

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2024
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14%
Summary Of Tax Credit Carryforwards	At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14%
Summary Of Tax Credit Carryforwards	At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and six months ended June 30, 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, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the three and six months ended June 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (61%) —% (21%) (1%) 220% (17%) (113%) (18%) 4% 16% 5% 14%
Summary Of Tax Credit Carryforwards	At June 30, 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 $386 $6 $1 Federal tax credits 2032-2044 631 405 216

Benefit Plans (Tables)

Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57
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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57
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 and six months ended June 30 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 Three Months Six Months Three Months Six Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $2 $2 $1 $— $1 $1 Interest cost 11 12 22 23 2 2 4 4 Expected return on plan assets (14) (13) (27) (26) (1) (1) (2) (2) Amortization of actuarial loss 6 7 12 14 — 1 — 1 $4 $7 $9 $13 $2 $2 $3 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $1 $1 $2 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (13) (13) (1) (1) (2) (2) Amortization of actuarial loss 3 3 5 6 — 1 — 1 $2 $3 $3 $5 $— $1 $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $1 $1 $1 $— $— $— $— Interest cost 5 5 10 10 1 1 2 2 Expected return on plan assets (6) (6) (12) (11) — — — — Amortization of actuarial loss 3 4 6 7 — — — — $3 $4 $5 $7 $1 $1 $2 $2
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $3 $7 $6 $2 $2 $4 $3 $1 $1 $3 $2 Income tax benefits 1 1 2 2 — — 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30, 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) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	6 Months Ended
	Jun. 30, 2024
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the six months ended June 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (1) — (1) Liabilities incurred (a) 355 102 253 Accretion expense 5 3 2 Balance, June 30 $603 $253 $350 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2024
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025
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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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 June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025
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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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 June 30, 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 Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,563 2024-2026 22,363 2024-2025 181,348 2024-2032 3,150 2024-2025 IPL 706 2024-2026 7,387 2024-2025 81,924 2024-2030 — — WPL 857 2024-2026 14,976 2024-2025 99,424 2024-2032 3,150 2024-2025
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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $68 $44 $52 $30 $16 $14 Non-current derivative assets 35 44 20 24 15 20 Current derivative liabilities 42 51 22 22 20 29 Non-current derivative liabilities 49 47 9 8 40 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 June 30, 2024 Derivative assets $103 $75 $72 $56 $31 $19 Derivative liabilities 91 63 31 15 60 48 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)	6 Months Ended
	Jun. 30, 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 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 June 30, 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 $73 $73 $— $— $73 $45 $45 $— $— $45 Commodity derivatives 103 — 46 57 103 88 — 59 29 88 Interest rate derivatives 3 — 3 — 3 1 — 1 — 1 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 91 — 85 6 91 98 — 93 5 98 Long-term debt (incl. current maturities) 9,704 — 9,352 — 9,352 9,034 — 8,677 — 8,677 IPL June 30, 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 $1 $1 $— $— $1 $45 $45 $— $— $45 Commodity derivatives 72 — 26 46 72 54 — 30 24 54 Deferred proceeds 171 — — 171 171 216 — — 216 216 Liabilities: Commodity derivatives 31 — 25 6 31 30 — 25 5 30 Long-term debt (incl. current maturities) 3,946 — 3,577 — 3,577 3,945 — 3,664 — 3,664 WPL June 30, 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 $72 $72 $— $— $72 $— $— $— $— $— Commodity derivatives 31 — 20 11 31 34 — 29 5 34 Liabilities: Commodity derivatives 60 — 60 — 60 68 — 68 — 68 Long-term debt 3,368 — 3,141 — 3,141 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 June 30 2024 2023 2024 2023 Beginning balance, April 1 $7 ($5) $184 $153 Total net losses included in changes in net assets (realized/unrealized) (5) (7) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (9) 5 (13) 22 Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($5) ($7) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (8) (11) — — Purchases 59 62 — — Sales (1) (1) — — Settlements (a) (23) (15) (45) (10) Ending balance, June 30 $51 $54 $171 $175 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 June 30 ($8) ($11) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2024 2023 2024 2023 Beginning balance, April 1 $5 $— $184 $153 Total net losses included in changes in net assets (realized/unrealized) (2) (13) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (7) 4 (13) 22 Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($2) ($13) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (6) (12) — — Purchases 45 51 — — Sales (1) (1) — — Settlements (a) (17) (13) (45) (10) Ending balance, June 30 $40 $41 $171 $175 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 June 30 ($6) ($12) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended June 30 2024 2023 Beginning balance, April 1 $2 ($5) Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 6 Purchases 14 11 Settlements (2) 1 Ending balance, June 30 $11 $13 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 June 30 ($3) $6 WPL Commodity Contract Derivative Assets and (Liabilities), net Six Months Ended June 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 1 Purchases 14 11 Settlements (6) (2) Ending balance, June 30 $11 $13 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 June 30 ($2) $1 (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 asset s (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2024 ($4) $55 ($4) $44 $— $11 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies (

Commitments And Contingencies (Tables)	6 Months Ended
	Jun. 30, 2024
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At June 30, 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 June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At June 30, 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 June 30, 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 $773 $316 $457 Coal 155 106 49 Other (a) 118 50 25 $1,046 $472 $531 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At June 30, 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)	6 Months Ended
	Jun. 30, 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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160
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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160
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. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2024 Revenues $789 $69 $10 $868 $26 $894 Operating income (loss) 131 1 (16) 116 14 130 Net income attributable to Alliant Energy common shareowners 82 5 87 Three Months Ended June 30, 2023 Revenues $799 $77 $13 $889 $23 $912 Operating income 200 2 7 209 8 217 Net income (loss) attributable to Alliant Energy common shareowners 161 (1) 160 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2024 Revenues $1,580 $273 $24 $1,877 $48 $1,925 Operating income (loss) 295 48 (11) 332 20 352 Net income attributable to Alliant Energy common shareowners 237 8 245 Six Months Ended June 30, 2023 Revenues $1,567 $353 $25 $1,945 $45 $1,990 Operating income 363 52 11 426 13 439 Net income attributable to Alliant Energy common shareowners 321 2 323 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $404 $40 $9 $453 Operating income (loss) 34 (1) (17) 16 Net income 18 Three Months Ended June 30, 2023 Revenues $431 $44 $12 $487 Operating income 105 — 5 110 Net income 89 Six Months Ended June 30, 2024 Revenues $795 $148 $23 $966 Operating income (loss) 91 21 (11) 101 Net income 81 Six Months Ended June 30, 2023 Revenues $819 $194 $24 $1,037 Operating income 171 27 8 206 Net income 161 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2024 Revenues $385 $29 $1 $415 Operating income 97 2 1 100 Net income 64 Three Months Ended June 30, 2023 Revenues $368 $33 $1 $402 Operating income 95 2 2 99 Net income 72 Six Months Ended June 30, 2024 Revenues $785 $125 $1 $911 Operating income 204 27 — 231 Net income 156 Six Months Ended June 30, 2023 Revenues $748 $159 $1 $908 Operating income 192 25 3 220 Net income 160

Related Parties (Tables)

Related Parties (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC billings to WPL $39 $44 $76 $78 WPL billings to ATC 4 5 7 11
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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $49 $48 $92 $88 $46 $43 $86 $80 Sales credited — 1 — 8 14 10 36 22 Purchases billed 105 94 201 187 16 2 23 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2024 December 31, 2023 June 30, 2024 December 31, 2023 Net payables to Corporate Services $138 $129 $67 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2024 2023 2024 2023 ATC billings to WPL $39 $44 $76 $78 WPL billings to ATC 4 5 7 11

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 73	$ 45
Money market fund investments weighted-average interest rate, percentage	5%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 1	45
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 72	$ 0
Money market fund investments weighted-average interest rate, percentage	5%

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Regulatory Matters [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 60	$ 0	$ 60	$ 0
IPL [Member]
Regulatory Matters [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 60	$ 0	$ 60	$ 0

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Regulatory assets	$ 2,345	$ 2,261
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	958	934
Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	408	194
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	334	347
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	197	273
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	95	102
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	89	120
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	43	44
IPL's Duane Arnold Energy Center PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	30	42
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	191	205
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,548	1,577
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	848	831
IPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	218	160
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	165	171
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	184	259
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	33	34
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	2	12
IPL [Member] | IPL's Duane Arnold Energy Center PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	30	42
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	68	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	797	684
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	110	103
WPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	190	34
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	169	176
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	13	14
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	62	68
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	87	108
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	43	44
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 123	$ 137

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,136	$ 1,130
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	601	566
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	374	366
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	50	65
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	51	48
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	60	85
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	618	644
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	296	299
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	232	242
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30	34
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	16	13
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	44	56
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	518	486
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	305	267
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	142	124
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20	31
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	35	35
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 16	$ 29

Property, Plant and Equipment (

Property, Plant and Equipment (Narrative) (Details) - WPL [Member] $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($) lease_renewal_period_option MW
Property, Plant and Equipment [Line Items]
Electric capacity of solar project | MW	1,100
Construction project cost target exceedance	$ 195
Sheboygan Falls Energy Facility
Property, Plant and Equipment [Line Items]
Financing lease, lease renewal periods remaining | lease_renewal_period_option	0
West Riverside Energy Center [Member]
Property, Plant and Equipment [Line Items]
Ownership interest, percent	56.60%
Electric Generation | Edgewater Unit 5
Property, Plant and Equipment [Line Items]
Net book value, Edgewater Unit 5	$ 496
Utility electric generation plant in service, Edgewater Unit 5	$ 806

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] - USD ($) $ in Millions	Jul. 31, 2024	Jun. 30, 2024
Receivables [Line Items]
Available capacity		$ 65
Maximum [Member]
Receivables [Line Items]
Limit on cash proceeds to be received from third-party		110
Subsequent Event [Member] | Maximum [Member]
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	$ 60
Financial Asset, Past Due [Member]
Receivables [Line Items]
Outstanding receivables past due		$ 16

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 110	$ 110	$ 110	$ 110
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 73	$ 101	$ 48	$ 79

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Receivables [Line Items]
Fair value of deferred proceeds	$ 171	$ 216
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	171	216
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	131	130
Unbilled utility revenues	94	98
Other receivables	2	1
Receivables sold to third party	227	229
Less: cash proceeds	45	1
Deferred proceeds	182	228
Less: allowance for expected credit losses	11	12
Fair value of deferred proceeds	$ 171	$ 216

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Receivables [Line Items]
Collections	$ 456	$ 514	$ 1,013	$ 1,104
Write-offs, net of recoveries	$ 2	$ 2	$ 5	$ 4

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (15)	$ (14)	$ (31)	$ (31)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(13)	(12)	(25)	(25)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(2)	(2)	(6)	(6)
Total [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (15)	$ (14)	$ (31)	$ (31)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	6 Months Ended
	Jun. 30, 2024 shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2024 (in shares)	256,096,848
Shareowner Direct Plan (in shares)	248,460
Equity-based compensation plans (in shares)	154,267
Shares outstanding, June 30, 2024 (in shares)	256,499,575

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 6,777
Beginning balance	$ 6,817	$ 6,328	6,777	$ 6,276
Net income attributable to common shareowners	87	160	245	323
Net income			245	323
Common stock dividends	(123)	(113)	(246)	(226)
Shareowner Direct Plan issuances	6	70	12	76
Equity-based compensation plans and other	3	3	1	0
Other comprehensive income (loss), net of tax	1	4	2	3
Ending balance	6,791		6,791
Ending balance	$ 6,791	$ 6,452	$ 6,791	$ 6,452
Common stock dividends (in dollars per share)	$ 0.48	$ 0.4525	$ 0.96	$ 0.905
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 3	$ 3	$ 3
Ending balance	3	3	3	3
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,033	2,780	3,030	2,777
Shareowner Direct Plan issuances	6	70	12	76
Equity-based compensation plans and other	3	4		1
Ending balance	3,042	2,854	3,042	2,854
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,791	3,559	3,756	3,509
Net income attributable to common shareowners	87	160	245	323
Common stock dividends	(123)	(113)	(246)	(226)
Ending balance	3,755	3,606	3,755	3,606
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2	(1)	1	0
Other comprehensive income (loss), net of tax	1	4	2	3
Ending balance	3	3	3	3
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(12)	(13)	(13)	(13)
Equity-based compensation plans and other		(1)	1	(1)
Ending balance	(12)	(14)	(12)	(14)
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,974
Beginning balance	4,037	3,810	3,974	3,808
Net income attributable to common shareowners	18	89	81	161
Net income	18	89	81	161
Common stock dividends	(50)	(70)	(100)	(140)
Capital contributions from parent	75	40	125	40
Ending balance	4,080		4,080
Ending balance	4,080	3,869	4,080	3,869
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33	33	33
Ending balance	33	33	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,937	2,807	2,887	2,807
Capital contributions from parent	75	40	125	40
Ending balance	3,012	2,847	3,012	2,847
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,067	970	1,054	968
Net income	18	89	81	161
Common stock dividends	(50)	(70)	(100)	(140)
Ending balance	1,035	989	1,035	989
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,897
Beginning balance	3,995	3,713	3,897	3,491
Net income attributable to common shareowners	64	72	156	160
Net income	64	72	156	160
Common stock dividends	(49)	(46)	(98)	(92)
Capital contributions from parent			55	180
Ending balance	4,010		4,010
Ending balance	4,010	3,739	4,010	3,739
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66	66	66
Ending balance	66	66	66	66
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,533	2,413	2,478	2,233
Capital contributions from parent			55	180
Ending balance	2,533	2,413	2,533	2,413
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,396	1,234	1,353	1,192
Net income	64	72	156	160
Common stock dividends	(49)	(46)	(98)	(92)
Ending balance	$ 1,411	$ 1,260	$ 1,411	$ 1,260

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2025	Dec. 31, 2023
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Payments to retire long-term debt	305	$ 404
Long-term debt, fair value	9,352			$ 8,677
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	450
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	250
Long-term debt, fair value	3,577			3,664
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	300
Long-term debt, fair value	3,141			$ 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
Senior Notes [Member] | 5.4% senior notes, due 2027 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 375
Interest rate, percent	5.40%
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	$ 570
Unamortized debt issuance costs	5
Long-term debt, fair value	$ 568
Shares included in diluted earnings per share (in shares)	0

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Jun. 30, 2024 USD ($)
Debt [Line Items]
Amount outstanding	$ 52
Weighted average interest rates	5.50%
Available credit facility capacity	$ 948
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0%
Available credit facility capacity	$ 250
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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 435	$ 391	$ 632	$ 793
Average amount outstanding (based on daily outstanding balances)	$ 275	$ 88	$ 381	$ 330
Weighted average interest rates	5.50%	5.30%	5.50%	4.80%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 19	$ 70	$ 19	$ 70
Average amount outstanding (based on daily outstanding balances)	$ 2	$ 6	$ 1	$ 3
Weighted average interest rates	5.50%	5.30%	5.50%	5.30%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 57	$ 91	$ 390	$ 349
Average amount outstanding (based on daily outstanding balances)	$ 8	$ 18	$ 131	$ 160
Weighted average interest rates	5.40%	5.20%	5.50%	4.80%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 894	$ 912	$ 1,925	$ 1,990
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	789	799	1,580	1,567
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	291	284	588	569
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	191	201	377	385
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	237	245	460	460
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	43	49	89	95
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	20	66	58
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69	77	273	353
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	38	42	165	210
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	22	80	110
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	3	6	9
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	22	24
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	13	24	25
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	20	22
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	4	3
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	23	48	45
Non-utility and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	23	48	45
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	453	487	966	1,037
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	404	431	795	819
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	151	151	301	294
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118	129	232	241
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118	130	229	236
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14	26	26
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	7	7	22
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	40	44	148	194
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	24	90	117
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	12	41	56
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	4	6
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	6	13	15
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	12	23	24
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	20	22
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	3	2
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	415	402	911	908
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	385	368	785	748
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	140	133	287	275
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	72	145	144
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	119	115	231	224
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	35	63	69
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23	13	59	36
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29	33	125	159
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	18	75	93
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	10	39	54
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	2	3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	4	9	9
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	1	1
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1	$ 1	$ 1	$ 1

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Taxes [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 60	$ 0	$ 60	$ 0
Steam Plant
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets	20		20
IPL [Member]
Income Taxes [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	60	0	60	0
Asset retirement obligation charge for IPL's steam assets	102	85	187	181
IPL [Member] | Steam Plant
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets	20		20
WPL [Member]
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets	$ 67	$ 67	$ 128	$ 133

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Effective Tax Rate [Line Items]
Overall income tax rate	(61.00%)	0%	(21.00%)	(1.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	220%	(17.00%)	(113.00%)	(18.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	4%	16%	5%	14%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2024 USD ($)
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 386
Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	631
IPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	6
IPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	405
WPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
WPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	$ 216

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 19
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	$ 9
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 8
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	234,773

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	11	12	22	23
Expected return on plan assets	(14)	(13)	(27)	(26)
Amortization of actuarial loss	6	7	12	14
Total	4	7	9	13
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0	1	1
Interest cost	2	2	4	4
Expected return on plan assets	(1)	(1)	(2)	(2)
Amortization of actuarial loss	0	1	0	1
Total	2	2	3	4
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	1	2
Interest cost	5	5	10	10
Expected return on plan assets	(6)	(6)	(13)	(13)
Amortization of actuarial loss	3	3	5	6
Total	2	3	3	5
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	2	2
Expected return on plan assets	(1)	(1)	(2)	(2)
Amortization of actuarial loss	0	1	0	1
Total	0	1	0	1
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1	1
Interest cost	5	5	10	10
Expected return on plan assets	(6)	(6)	(12)	(11)
Amortization of actuarial loss	3	4	6	7
Total	3	4	5	7
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	2	2
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	0	0	0	0
Total	$ 1	$ 1	$ 2	$ 2

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Compensation expense	$ 3	$ 3	$ 7	$ 6
Income tax benefits	1	1	2	2
IPL [Member]
Compensation expense	2	2	4	3
Income tax benefits	0	0	1	1
WPL [Member]
Compensation expense	1	1	3	2
Income tax benefits	$ 0	$ 0	$ 1	$ 1

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	6 Months Ended
	Jun. 30, 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	127,267
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 46.04
Performance Shares (net income and diversity metrics) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	145,449
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.49
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	128,620
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.57

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 246
Revisions in estimated cash flows			(2)
Liabilities settled			(1)
Liabilities incurred			355
Accretion expense			5
Balance, June 30	$ 603		603
Steam Plant
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligation charge for IPL's steam assets	20		20
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			148
Revisions in estimated cash flows			0
Liabilities settled			0
Liabilities incurred			102
Accretion expense			3
Balance, June 30	253		253
Asset retirement obligation charge for IPL's steam assets	102	$ 85	187	$ 181
IPL [Member] | Steam Plant
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligation charge for IPL's steam assets	20		20
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			98
Revisions in estimated cash flows			(2)
Liabilities settled			(1)
Liabilities incurred			253
Accretion expense			2
Balance, June 30	350		350
Asset retirement obligation charge for IPL's steam assets	$ 67	$ 67	$ 128	$ 133

Derivative Instruments (Narrati

Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Derivative Instruments [Line Items]
Non-current interest rate derivative assets	$ 160		$ 160		$ 177
Accumulated other comprehensive income, interest rate swap	3		3		$ 1
Interest expense, interest rate swap	108	$ 96	215	$ 190
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		3
Accumulated other comprehensive income, interest rate swap	3		3
Interest expense, interest rate swap	$ 1	$ 1	$ 2	$ 1

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands	6 Months Ended
	Jun. 30, 2024 Dekatherms MWh gal
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,563
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	706
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	857
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	22,363
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	7,387
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	14,976
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	181,348
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	81,924
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	99,424
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,150
Diesel Fuel (Gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	0
Diesel Fuel (Gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,150

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 68	$ 44
Non-current derivative assets	35	44
Current derivative liabilities	42	51
Non-current derivative liabilities	49	47
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	52	30
Non-current derivative assets	20	24
Current derivative liabilities	22	22
Non-current derivative liabilities	9	8
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	16	14
Non-current derivative assets	15	20
Current derivative liabilities	20	29
Non-current derivative liabilities	$ 40	$ 39

Derivative Instruments (Balance

Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$ 103	$ 88
Derivative assets, Net	75	47
Derivative liabilities, Gross (as reported)	91	98
Derivative liabilities, Net	63	57
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	72	54
Derivative assets, Net	56	32
Derivative liabilities, Gross (as reported)	31	30
Derivative liabilities, Net	15	8
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	31	34
Derivative assets, Net	19	15
Derivative liabilities, Gross (as reported)	60	68
Derivative liabilities, Net	$ 48	$ 49

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Carrying Amount [Member]
Assets:
Money market fund investments	$ 73	$ 45
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	9,704	9,034
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	1	45
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	3,946	3,945
Carrying Amount [Member] | WPL [Member]
Assets:
Money market fund investments	72	0
Liabilities:
Long-term debt (incl. current maturities)	3,368	3,070
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	103	88
Liabilities:
Derivatives	91	98
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	72	54
Liabilities:
Derivatives	31	30
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	31	34
Liabilities:
Derivatives	60	68
Carrying Amount [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Money market fund investments	73	45
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	9,352	8,677
IPL [Member]
Assets:
Money market fund investments	1	45
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	3,577	3,664
WPL [Member]
Assets:
Money market fund investments	72	0
Liabilities:
Long-term debt (incl. current maturities)	3,141	2,933
Commodity Contracts [Member]
Assets:
Derivatives	103	88
Liabilities:
Derivatives	91	98
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	72	54
Liabilities:
Derivatives	31	30
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	31	34
Liabilities:
Derivatives	60	68
Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Level 1 [Member]
Assets:
Money market fund investments	73	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	1	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Assets:
Money market fund investments	72	0
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)	9,352	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)	3,577	3,664
Level 2 [Member] | WPL [Member]
Assets:
Money market fund investments	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,141	2,933
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	46	59
Liabilities:
Derivatives	85	93
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	26	30
Liabilities:
Derivatives	25	25
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	20	29
Liabilities:
Derivatives	60	68
Level 2 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	3	1
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	171	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | WPL [Member]
Assets:
Money market fund investments	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	57	29
Liabilities:
Derivatives	6	5
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	46	24
Liabilities:
Derivatives	6	5
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	11	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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 7	$ (5)	$ 24	$ 19
Total net gains (losses) included in changes in net assets (realized/unrealized)	(5)	(7)	(8)	(11)
Purchases	59	62	59	62
Sales	(1)	(1)	(1)	(1)
Settlements	(9)	5	(23)	(15)
Ending balance	51	54	51	54
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 June 30	(5)	(7)	(8)	(11)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5	0	19	16
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	(13)	(6)	(12)
Purchases	45	51	45	51
Sales	(1)	(1)	(1)	(1)
Settlements	(7)	4	(17)	(13)
Ending balance	40	41	40	41
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 June 30	(2)	(13)	(6)	(12)
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2	(5)	5	3
Total net gains (losses) included in changes in net assets (realized/unrealized)	(3)	6	(2)	1
Purchases	14	11	14	11
Settlements	(2)	1	(6)	(2)
Ending balance	11	13	11	13
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 June 30	(3)	6	(2)	1
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	184	153	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(13)	22	(45)	(10)
Ending balance	171	175	171	175
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 June 30	0	0	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	184	153	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	(13)	22	(45)	(10)
Ending balance	171	175	171	175
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 June 30	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 51	$ 7	$ 24	$ 54	$ (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	(4)
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	55		21
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	40	5	19	41	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	(4)
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	44		16
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	11	$ 2	5	$ 13	$ (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	$ 11		$ 5

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2024
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,046
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			472
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 531
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			54%
Federal Energy Regulatory Commission [Member]
Commitments and Contingencies [Line Items]
MISO base return on equity, percentage	10.02%	9.88%
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			$ 51
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent			6%
Obligations, maximum			$ 49
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			116
Capital Purchase Commitment [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			38
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			76
Purchased Power [Member] | Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			17
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			147
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			$ 50

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,046
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	472
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	531
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	773
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	316
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	457
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	155
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	106
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	49
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	118
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	50
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	6 Months Ended
	Jun. 30, 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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 894	$ 912	$ 1,925	$ 1,990
Operating income (loss)	130	217	352	439
Net income (loss) attributable to common shareowners	87	160	245	323
Net income			245	323
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	453	487	966	1,037
Operating income (loss)	16	110	101	206
Net income (loss) attributable to common shareowners	18	89	81	161
Net income	18	89	81	161
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	415	402	911	908
Operating income (loss)	100	99	231	220
Net income (loss) attributable to common shareowners	64	72	156	160
Net income	64	72	156	160
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	789	799	1,580	1,567
Operating income (loss)	131	200	295	363
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	404	431	795	819
Operating income (loss)	34	105	91	171
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	385	368	785	748
Operating income (loss)	97	95	204	192
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	69	77	273	353
Operating income (loss)	1	2	48	52
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	40	44	148	194
Operating income (loss)	(1)	0	21	27
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	29	33	125	159
Operating income (loss)	2	2	27	25
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10	13	24	25
Operating income (loss)	(16)	7	(11)	11
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	9	12	23	24
Operating income (loss)	(17)	5	(11)	8
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1	1	1	1
Operating income (loss)	1	2	0	3
Non-utility and Other [Member]
Segment Reporting Information [Line Items]
Revenues	26	23	48	45
Operating income (loss)	14	8	20	13
Net income (loss) attributable to common shareowners	5	(1)	8	2
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	868	889	1,877	1,945
Operating income (loss)	116	209	332	426
Net income (loss) attributable to common shareowners	$ 82	$ 161	$ 237	$ 321

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
WPL [Member] | WPL Owed ATC LLC [Member] | Related Party [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 11	$ 10

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 49	$ 48	$ 92	$ 88
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	46	43	86	80
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	0	1	0	8
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	14	10	36	22
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	105	94	201	187
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 16	$ 2	$ 23	$ 17

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Related Party [Member] - Corporate Services [Member] - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 138	$ 129
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 67	$ 72

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - WPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 39	$ 44	$ 76	$ 78
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 4	$ 5	$ 7	$ 11