Document And Entity Information	3 Months Ended
Document And Entity Information	Mar. 31, 2025 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2025
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	256,876,299
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	Q1
Amendment Flag	false
IPL [Member]
Entity Information [Line Items]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Incorporation, State or Country Code	IA
Entity Address, Address Line One	Alliant Energy Tower
Entity Address, City or Town	Cedar Rapids
Entity Address, State or Province	IA
Entity Address, Postal Zip Code	52401
City Area Code	319
Local Phone Number	786-4411
Entity File Number	1-4117
Entity Tax Identification Number	42-0331370
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Information [Line Items]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	0-337
Entity Tax Identification Number	39-0714890
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Revenues:
Electric utility	$ 853	$ 791
Gas utility	240	205
Other utility	13	13
Non-utility	22	22
Total revenues	1,128	1,031
Operating expenses:
Electric production fuel and purchased power	175	163
Electric transmission service	158	152
Cost of gas sold	137	114
Other operation and maintenance	160	160
Depreciation and amortization	211	189
Taxes other than income taxes	30	31
Total operating expenses	871	809
Operating income	257	222
Other (income) and deductions:
Interest expense	119	107
Equity income from unconsolidated investments, net	(13)	(15)
Allowance for funds used during construction	(18)	(19)
Other	3	1
Total other (income) and deductions	91	74
Income before income taxes	166	148
Income tax expense (benefit)	(47)	(10)
Net income attributable to common shareowners	$ 213	$ 158
Weighted average number of common shares outstanding:
Basic (in shares)	256,800	256,200
Diluted (in shares)	257,200	256,500
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.83	$ 0.62
Diluted (in dollars per share)	$ 0.83	$ 0.62
IPL [Member]
Revenues:
Electric utility	$ 430	$ 392
Gas utility	118	108
Other utility	12	13
Total revenues	560	513
Operating expenses:
Electric production fuel and purchased power	67	67
Electric transmission service	108	103
Cost of gas sold	65	60
Other operation and maintenance	82	86
Depreciation and amortization	115	96
Taxes other than income taxes	15	16
Total operating expenses	452	428
Operating income	108	85
Other (income) and deductions:
Interest expense	47	42
Allowance for funds used during construction	(9)	(10)
Total other (income) and deductions	38	32
Income before income taxes	70	53
Income tax expense (benefit)	(40)	(10)
Net income attributable to common shareowners	110	63
WPL [Member]
Revenues:
Electric utility	423	399
Gas utility	122	97
Other utility	1	0
Total revenues	546	496
Operating expenses:
Electric production fuel and purchased power	108	96
Electric transmission service	50	49
Cost of gas sold	72	53
Other operation and maintenance	67	63
Depreciation and amortization	93	90
Taxes other than income taxes	14	14
Total operating expenses	404	365
Operating income	142	131
Other (income) and deductions:
Interest expense	43	41
Allowance for funds used during construction	(9)	(9)
Other	3	1
Total other (income) and deductions	37	33
Income before income taxes	105	98
Income tax expense (benefit)	(5)	6
Net income attributable to common shareowners	$ 110	$ 92

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Current assets:
Cash and cash equivalents	$ 25	$ 81
Accounts receivable, less allowance for expected credit losses	361	427
Production fuel, at weighted average cost	53	54
Gas stored underground, at weighted average cost	16	55
Materials and supplies, at weighted average cost	196	186
Regulatory assets	172	210
Other	146	171
Total current assets	969	1,184
Property, plant and equipment, net	19,022	18,701
Investments:
ATC Holdings	426	415
Other	224	224
Total investments	650	639
Other assets:
Regulatory assets	2,102	2,064
Deferred charges and other	108	126
Total other assets	2,210	2,190
Total assets	22,851	22,714
Current liabilities:
Current maturities of long-term debt	1,371	1,171
Commercial paper	678	558
Accounts payable	405	532
Regulatory liabilities	109	69
Other	325	385
Total current liabilities	2,888	2,715
Long-term debt, net (excluding current portion)	8,580	8,677
Other liabilities:
Deferred tax liabilities	2,147	2,188
Regulatory liabilities	974	959
Pension and other benefit obligations	210	224
Other	959	947
Total other liabilities	4,290	4,318
Commitments and contingencies (Note 12)
Common equity:
Common stock	3	3
Additional paid-in capital	3,066	3,060
Retained earnings	4,037	3,954
Accumulated other comprehensive income (loss)	0	1
Shares in deferred compensation trust - 347,775 and 372,116 shares at a weighted average cost of $37.17 and $36.56 per share	(13)	(14)
Total common equity	7,093	7,004
Total liabilities and equity	22,851	22,714
IPL [Member]
Current assets:
Cash and cash equivalents	12	29
Accounts receivable, less allowance for expected credit losses	112	192
Production fuel, at weighted average cost	27	30
Gas stored underground, at weighted average cost	5	25
Materials and supplies, at weighted average cost	121	113
Regulatory assets	71	77
Other	44	43
Total current assets	392	509
Property, plant and equipment, net	9,584	9,336
Other assets:
Regulatory assets	1,522	1,509
Deferred charges and other	42	53
Total other assets	1,564	1,562
Total assets	11,540	11,407
Current liabilities:
Current maturities of long-term debt	300	300
Commercial paper	109	50
Accounts payable	193	263
Accounts payable to associated companies	39	47
Accrued taxes	78	77
Accrued interest	38	48
Regulatory liabilities	76	54
Other	72	89
Total current liabilities	905	928
Long-term debt, net (excluding current portion)	3,891	3,790
Other liabilities:
Deferred tax liabilities	1,171	1,179
Regulatory liabilities	485	492
Pension and other benefit obligations	45	46
Other	516	511
Total other liabilities	2,217	2,228
Commitments and contingencies (Note 12)
Common equity:
Common stock	33	33
Additional paid-in capital	3,257	3,212
Retained earnings	1,237	1,216
Total common equity	4,527	4,461
Total liabilities and equity	11,540	11,407
WPL [Member]
Current assets:
Cash and cash equivalents	11	51
Accounts receivable, less allowance for expected credit losses	235	220
Production fuel, at weighted average cost	26	24
Gas stored underground, at weighted average cost	11	30
Materials and supplies, at weighted average cost	70	69
Regulatory assets	101	133
Prepaid gross receipts tax	39	51
Other	40	57
Total current assets	533	635
Property, plant and equipment, net	8,937	8,861
Other assets:
Regulatory assets	580	555
Deferred charges and other	51	55
Total other assets	631	610
Total assets	10,101	10,106
Current liabilities:
Commercial paper	212	183
Accounts payable	155	209
Accrued interest	41	44
Regulatory liabilities	33	15
Other	85	94
Total current liabilities	526	545
Long-term debt, net (excluding current portion)	3,371	3,370
Other liabilities:
Deferred tax liabilities	828	865
Regulatory liabilities	489	467
Pension and other benefit obligations	92	102
Other	659	656
Total other liabilities	2,068	2,090
Commitments and contingencies (Note 12)
Common equity:
Common stock	66	66
Additional paid-in capital	2,533	2,533
Retained earnings	1,537	1,502
Total common equity	4,136	4,101
Total liabilities and equity	$ 10,101	$ 10,106

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2025	Dec. 31, 2024
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)	256,876,299	256,690,222
Shares in deferred compensation trust (in shares)	347,775	372,116
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 37.17	$ 36.56
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 Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Cash flows from operating activities:
Net income	$ 213	$ 158
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	211	189
Deferred tax expense (benefit) and tax credits	(51)	(12)
Other	1	(6)
Other changes in assets and liabilities:
Accounts receivable	(128)	(116)
Gas stored underground	39	27
Derivative assets	6	30
Regulatory assets	(12)	35
Accounts payable	(45)	12
Regulatory liabilities	53	(14)
Other	(38)	4
Net cash flows from operating activities	249	307
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(554)	(478)
Other construction and acquisition expenditures	(28)	(32)
Cash receipts on sold receivables	192	155
Other	(14)	2
Net cash flows from (used for) investing activities	(404)	(353)
Cash flows from (used for) financing activities:
Common stock dividends	(130)	(123)
Proceeds from issuance of long-term debt	0	597
Payments to retire long-term debt	0	(300)
Net change in commercial paper	220	(141)
Other	9	(15)
Net cash flows from (used for) financing activities	99	18
Net increase (decrease) in cash, cash equivalents and restricted cash	(56)	(28)
Cash, cash equivalents and restricted cash at beginning of period	81	63
Cash, cash equivalents and restricted cash at end of period	25	35
Supplemental cash flows information:
Interest	(139)	(97)
Income taxes, net	0	(2)
Significant non-cash investing and financing activities:
Accrued capital expenditures	144	204
Beneficial interest obtained in exchange for securitized accounts receivable	86	184
IPL [Member]
Cash flows from operating activities:
Net income	110	63
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	115	96
Deferred tax expense (benefit) and tax credits	(30)	(5)
Other	(6)	(6)
Other changes in assets and liabilities:
Accounts receivable	(112)	(119)
Accounts payable	(21)	(7)
Other	3	54
Net cash flows from operating activities	59	76
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(376)	(253)
Cash receipts on sold receivables	192	155
Other	(6)	(9)
Net cash flows from (used for) investing activities	(190)	(107)
Cash flows from (used for) financing activities:
Common stock dividends	(89)	(50)
Capital contributions from parent	45	50
Net change in commercial paper	159	0
Other	(1)	(10)
Net cash flows from (used for) financing activities	114	(10)
Net increase (decrease) in cash, cash equivalents and restricted cash	(17)	(41)
Cash, cash equivalents and restricted cash at beginning of period	29	53
Cash, cash equivalents and restricted cash at end of period	12	12
Supplemental cash flows information:
Interest	(58)	(32)
Income taxes, net	0	(2)
Significant non-cash investing and financing activities:
Accrued capital expenditures	81	110
Beneficial interest obtained in exchange for securitized accounts receivable	86	184
WPL [Member]
Cash flows from operating activities:
Net income	110	92
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	93	90
Other	(22)	(11)
Other changes in assets and liabilities:
Regulatory assets	6	29
Accounts payable	(24)	15
Regulatory liabilities	37	(18)
Deferred income taxes	(24)	(7)
Other	14	51
Net cash flows from operating activities	190	241
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(178)	(225)
Other	(7)	12
Net cash flows from (used for) investing activities	(185)	(213)
Cash flows from (used for) financing activities:
Common stock dividends	(75)	(49)
Capital contributions from parent	0	55
Proceeds from issuance of long-term debt	0	297
Net change in commercial paper	29	(318)
Other	1	(9)
Net cash flows from (used for) financing activities	(45)	(24)
Net increase (decrease) in cash, cash equivalents and restricted cash	(40)	4
Cash, cash equivalents and restricted cash at beginning of period	51	7
Cash, cash equivalents and restricted cash at end of period	11	11
Supplemental cash flows information:
Interest	(47)	(40)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 56	$ 91

Summary Of Significant Accounting Policies	3 Months Ended
Summary Of Significant Accounting Policies	Mar. 31, 2025
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters

3 Months Ended

Mar. 31, 2025

Public Utilities, General Disclosures [Line Items]

Regulatory Matters

REGULATORY MATTERS

Regulatory Assets and Regulatory Liabilities -

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Derivatives - Refer to Note 10 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

IPL [Member]

Public Utilities, General Disclosures [Line Items]

Regulatory Matters

REGULATORY MATTERS

Regulatory Assets and Regulatory Liabilities -

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Derivatives - Refer to Note 10 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

WPL [Member]

Public Utilities, General Disclosures [Line Items]

Regulatory Matters

REGULATORY MATTERS

Regulatory Assets and Regulatory Liabilities -

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Derivatives - Refer to Note 10 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the three months ended March 31, 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

Receivables

3 Months Ended

Mar. 31, 2025

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. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of March 31, 2025, IPL had no available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):



	2025	2024
Maximum outstanding aggregate cash proceeds	$110	$79
Average outstanding aggregate cash proceeds	108	24

The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):


	March 31, 2025	December 31, 2024
Customer accounts receivable	$139	$137
Unbilled utility revenues	72	108

Receivables sold to third party	211	245
Less: cash proceeds	110	70
Deferred proceeds	101	175
Less: allowance for expected credit losses	15	12
Fair value of deferred proceeds	$86	$163

As of March 31, 2025, outstanding receivables past due under the Receivables Agreement were $27 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):



	2025	2024
Collections	$607	$557
Write-offs, net of recoveries	3	3

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. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of March 31, 2025, IPL had no available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):



	2025	2024
Maximum outstanding aggregate cash proceeds	$110	$79
Average outstanding aggregate cash proceeds	108	24

The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):


	March 31, 2025	December 31, 2024
Customer accounts receivable	$139	$137
Unbilled utility revenues	72	108

Receivables sold to third party	211	245
Less: cash proceeds	110	70
Deferred proceeds	101	175
Less: allowance for expected credit losses	15	12
Fair value of deferred proceeds	$86	$163

As of March 31, 2025, outstanding receivables past due under the Receivables Agreement were $27 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):



	2025	2024
Collections	$607	$557
Write-offs, net of recoveries	3	3

Investments

3 Months Ended

Mar. 31, 2025

Schedule of Equity Method Investments [Line Items]

Investments

INVESTMENTS

Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):



	2025	2024
ATC Holdings	($14)	($12)


Other	1	(3)
	($13)	($15)

Common Equity

3 Months Ended

Mar. 31, 2025

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, 2025			256,690,222


Shareowner Direct Plan			99,700
Equity-based compensation plans			86,377

Shares outstanding, March 31, 2025			256,876,299

Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

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, 2025			256,690,222


Shareowner Direct Plan			99,700
Equity-based compensation plans			86,377

Shares outstanding, March 31, 2025			256,876,299

Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

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, 2025			256,690,222


Shareowner Direct Plan			99,700
Equity-based compensation plans			86,377

Shares outstanding, March 31, 2025			256,876,299

Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

+ Details

Debt

3 Months Ended

Mar. 31, 2025

Debt [Line Items]

Debt

DEBT

NOTE 6(a) Short-term Debt - In March 2025, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL, within the $1.3 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

NOTE 6(b) Long-term Debt - In March 2025, AEF entered into a $300 million variable rate (5% as of March 31, 2025) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2026. This term loan credit agreement amended and restated the term loan credit agreement that expired in March 2025, 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.

As of March 31, 2025, $100 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s balance sheets due to the existence of the long-term single credit facility that back-stops this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis. As of March 31, 2025, this commercial paper balance had a 4.6% interest rate. In the second quarter of 2025, Alliant Energy’s and IPL’s commercial paper classified as long-term debt increased $50 million.

Convertible Senior Notes - As of March 31, 2025, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (the Notes) to convert their Notes were not met, and the Notes were classified as “Current maturities of long-term debt” on Alliant Energy’s balance sheet. As of March 31, 2025, the net carrying amount of the Notes was $572 million, with unamortized debt issuance costs of $3 million, and the estimated fair value (Level 2) of the Notes was $617 million. As of March 31, 2025, 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 6(a) Short-term Debt - In March 2025, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL, within the $1.3 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

NOTE 6(b) Long-term Debt - In March 2025, AEF entered into a $300 million variable rate (5% as of March 31, 2025) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2026. This term loan credit agreement amended and restated the term loan credit agreement that expired in March 2025, 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.

As of March 31, 2025, $100 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s balance sheets due to the existence of the long-term single credit facility that back-stops this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis. As of March 31, 2025, this commercial paper balance had a 4.6% interest rate. In the second quarter of 2025, Alliant Energy’s and IPL’s commercial paper classified as long-term debt increased $50 million.

Convertible Senior Notes - As of March 31, 2025, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (the Notes) to convert their Notes were not met, and the Notes were classified as “Current maturities of long-term debt” on Alliant Energy’s balance sheet. As of March 31, 2025, the net carrying amount of the Notes was $572 million, with unamortized debt issuance costs of $3 million, and the estimated fair value (Level 2) of the Notes was $617 million. As of March 31, 2025, 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.

WPL [Member]

Debt [Line Items]

Debt

DEBT

NOTE 6(a) Short-term Debt - In March 2025, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL, within the $1.3 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

NOTE 6(b) Long-term Debt - In March 2025, AEF entered into a $300 million variable rate (5% as of March 31, 2025) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2026. This term loan credit agreement amended and restated the term loan credit agreement that expired in March 2025, 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.

As of March 31, 2025, $100 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s balance sheets due to the existence of the long-term single credit facility that back-stops this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis. As of March 31, 2025, this commercial paper balance had a 4.6% interest rate. In the second quarter of 2025, Alliant Energy’s and IPL’s commercial paper classified as long-term debt increased $50 million.

Convertible Senior Notes - As of March 31, 2025, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (the Notes) to convert their Notes were not met, and the Notes were classified as “Current maturities of long-term debt” on Alliant Energy’s balance sheet. As of March 31, 2025, the net carrying amount of the Notes was $572 million, with unamortized debt issuance costs of $3 million, and the estimated fair value (Level 2) of the Notes was $617 million. As of March 31, 2025, 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.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481544/470-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481544/470-10-50-6

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477092/405-40-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477092/405-40-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477092/405-40-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477092/405-40-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 405
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477092/405-40-50-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/470/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 26: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 27: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

+ Details

Revenues

3 Months Ended

Mar. 31, 2025

Disaggregation of Revenue [Line Items]

Revenues from Contracts with Customers

REVENUES

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

IPL [Member]

Disaggregation of Revenue [Line Items]

Revenues from Contracts with Customers

REVENUES

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

WPL [Member]

Disaggregation of Revenue [Line Items]

Revenues from Contracts with Customers

REVENUES

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-9

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-10

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-15

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-13

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org/606/tableOfContent

+ Details

Income Taxes

3 Months Ended

Mar. 31, 2025

Income Taxes [Line Items]

Income Taxes

INCOME TAXES

Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Deferred Tax Assets and Liabilities -

Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

IPL [Member]

Income Taxes [Line Items]

Income Taxes

INCOME TAXES

Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Deferred Tax Assets and Liabilities -

Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

WPL [Member]

Income Taxes [Line Items]

Income Taxes

INCOME TAXES

Income Tax Rates - Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Deferred Tax Assets and Liabilities -

Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

- Definition

The entire disclosure for income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12C

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477891/740-270-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/740/tableOfContent

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-14

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-21

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-17

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479360/740-10-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482603/740-30-50-2

+ Details

Benefit Plans

3 Months Ended

Mar. 31, 2025

Benefit Plans

BENEFIT PLANS

NOTE 9(a) Pension and OPEB Plans -

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

As of March 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years.

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

As of March 31, 2025, 408,289 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

IPL [Member]

Benefit Plans

BENEFIT PLANS

NOTE 9(a) Pension and OPEB Plans -

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

As of March 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years.

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

As of March 31, 2025, 408,289 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

WPL [Member]

Benefit Plans

BENEFIT PLANS

NOTE 9(a) Pension and OPEB Plans -

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

As of March 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $22 million, $11 million and $10 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years.

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

As of March 31, 2025, 408,289 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Derivative Instruments

3 Months Ended

Mar. 31, 2025

Derivative Instruments [Line Items]

Derivative Instruments

DERIVATIVE INSTRUMENTS

Commodity Derivatives -

Notional Amounts - As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Based on IPL’s and WPL’s cost recovery mechanisms, the 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 March 31, 2025 and December 31, 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

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.

IPL [Member]

Derivative Instruments [Line Items]

Derivative Instruments

DERIVATIVE INSTRUMENTS

Commodity Derivatives -

Notional Amounts - As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Based on IPL’s and WPL’s cost recovery mechanisms, the 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 March 31, 2025 and December 31, 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

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

WPL [Member]

Derivative Instruments [Line Items]

Derivative Instruments

DERIVATIVE INSTRUMENTS

Commodity Derivatives -

Notional Amounts - As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Based on IPL’s and WPL’s cost recovery mechanisms, the 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 March 31, 2025 and December 31, 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

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

3 Months Ended

Mar. 31, 2025

Fair Value Measurements

FAIR VALUE MEASUREMENTS

Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

IPL [Member]

Fair Value Measurements

FAIR VALUE MEASUREMENTS

Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

WPL [Member]

Fair Value Measurements

FAIR VALUE MEASUREMENTS

Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 107
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-107

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 940
-SubTopic 820
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478119/940-820-50-1

+ Details

Commitments And Contingencies

3 Months Ended

Mar. 31, 2025

Commitments and Contingencies Disclosure

COMMITMENTS AND CONTINGENCIES

NOTE 12(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, and improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At March 31, 2025, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $301 million, $136 million and $163 million, respectively.

NOTE 12(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

NOTE 12(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, has guaranteed 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.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of March 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $54 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 March 31, 2025 and December 31, 2024.

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 purchased power agreement (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 $43 million as of March 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2025 and December 31, 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of March 31, 2025, IPL and WPL provided indemnifications associated with $193 million and $121 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.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of March 31, 2025, IPL’s and WPL’s related guarantees were approximately $6 million and $15 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of March 31, 2025.

NOTE 12(d) Environmental Matters -

Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act.

IPL [Member]

Commitments and Contingencies Disclosure

COMMITMENTS AND CONTINGENCIES

NOTE 12(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, and improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At March 31, 2025, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $301 million, $136 million and $163 million, respectively.

NOTE 12(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

NOTE 12(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, has guaranteed 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.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of March 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $54 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 March 31, 2025 and December 31, 2024.

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 purchased power agreement (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 $43 million as of March 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2025 and December 31, 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of March 31, 2025, IPL and WPL provided indemnifications associated with $193 million and $121 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.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of March 31, 2025, IPL’s and WPL’s related guarantees were approximately $6 million and $15 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of March 31, 2025.

NOTE 12(d) Environmental Matters -

Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act.

WPL [Member]

Commitments and Contingencies Disclosure

COMMITMENTS AND CONTINGENCIES

NOTE 12(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, and improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At March 31, 2025, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $301 million, $136 million and $163 million, respectively.

NOTE 12(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

NOTE 12(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, has guaranteed 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.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of March 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $54 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 March 31, 2025 and December 31, 2024.

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 purchased power agreement (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 $43 million as of March 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of March 31, 2025 and December 31, 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of March 31, 2025, IPL and WPL provided indemnifications associated with $193 million and $121 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.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of March 31, 2025, IPL’s and WPL’s related guarantees were approximately $6 million and $15 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of March 31, 2025.

NOTE 12(d) Environmental Matters -

Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act.

Segments Of Business

3 Months Ended

Mar. 31, 2025

Segment Reporting Information [Line Items]

Segments Of Business

SEGMENTS OF BUSINESS

Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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 reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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 reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 48
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-48

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (ee)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 5: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 10: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-31

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-34

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-26C

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-26B

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-15

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-40

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/280/tableOfContent

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-26

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-41

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-21

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-21

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-32

+ Details

Related Parties

3 Months Ended

Mar. 31, 2025

Related Parties

RELATED PARTIES

Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):



	2025	2024
ATC billings to WPL	$38	$37
WPL billings to ATC	6	3

WPL owed ATC net amounts of $10 million as of March 31, 2025 and $10 million as of December 31, 2024.

IPL [Member]

Related Parties

RELATED PARTIES

Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

WPL [Member]

Related Parties

RELATED PARTIES

Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):



	2025	2024
ATC billings to WPL	$38	$37
WPL billings to ATC	6	3

WPL owed ATC net amounts of $10 million as of March 31, 2025 and $10 million as of December 31, 2024.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

+ Details

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Pay vs Performance Disclosure
Net income	$ 213	$ 158

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 60
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476176/805-60-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 323
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Subparagraph (g)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478666/740-323-65-2

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481687/323-10-50-3

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482765/220-10-50-6

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480175/815-40-65-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-8

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-11

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-11

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483443/250-10-50-4

Reference 17: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479168/946-830-55-10

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479105/946-220-45-7

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-3

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 23: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1A

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480097/470-10-S99-1B

Reference 32: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482689/260-10-45-60B

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-7

Reference 34: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 35: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-1A

Reference 36: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-1B

Reference 37: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

+ Details

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2025
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 Accounting Policies (Policy)	3 Months Ended
Summary Of Significant Accounting Policies (Policy)	Mar. 31, 2025
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
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 Securities and Exchange Commission. 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 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2025

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

IPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

WPL [Member]

Regulatory Assets [Line Items]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$1,011	$989	$884	$870	$127	$119
Asset retirement obligations	414	401	289	281	125	120
Pension and OPEB costs	312	315	156	157	156	158
Assets retired early	173	180	162	168	11	12
Commodity cost recovery	56	68	2	2	54	66
Derivatives	53	60	11	15	42	45
Non-service pension and OPEB costs	53	51	20	19	33	32
WPL’s Western Wisconsin gas distribution expansion investments	41	42	—	—	41	42


Other	161	168	69	74	92	94
	$2,274	$2,274	$1,593	$1,586	$681	$688

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):


	Alliant Energy		IPL		WPL
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Tax-related	$595	$582	$276	$286	$319	$296
Cost of removal obligations	341	347	201	205	140	142
Derivatives	61	53	31	29	30	24
Commodity cost recovery	40	17	27	12	13	5




Other	46	29	26	14	20	15
	$1,083	$1,028	$561	$546	$522	$482

Receivables (Tables)

3 Months Ended

Mar. 31, 2025

Receivables [Line Items]

Maximum And Average Outstanding Cash Proceeds

IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):



	2025	2024
Maximum outstanding aggregate cash proceeds	$110	$79
Average outstanding aggregate cash proceeds	108	24

Attributes of Receivables Sold Under the Receivables Agreement

The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):


	March 31, 2025	December 31, 2024
Customer accounts receivable	$139	$137
Unbilled utility revenues	72	108

Receivables sold to third party	211	245
Less: cash proceeds	110	70
Deferred proceeds	101	175
Less: allowance for expected credit losses	15	12
Fair value of deferred proceeds	$86	$163

Additional Attributes Of Receivables Sold Under The Receivables Agreement

Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):



	2025	2024
Collections	$607	$557
Write-offs, net of recoveries	3	3

IPL [Member]

Receivables [Line Items]

Maximum And Average Outstanding Cash Proceeds

IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):



	2025	2024
Maximum outstanding aggregate cash proceeds	$110	$79
Average outstanding aggregate cash proceeds	108	24

Attributes of Receivables Sold Under the Receivables Agreement

The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):


	March 31, 2025	December 31, 2024
Customer accounts receivable	$139	$137
Unbilled utility revenues	72	108

Receivables sold to third party	211	245
Less: cash proceeds	110	70
Deferred proceeds	101	175
Less: allowance for expected credit losses	15	12
Fair value of deferred proceeds	$86	$163

Additional Attributes Of Receivables Sold Under The Receivables Agreement

Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):



	2025	2024
Collections	$607	$557
Write-offs, net of recoveries	3	3

Investments (Tables)

3 Months Ended

Mar. 31, 2025

Schedule of Equity Method Investments [Line Items]

Unconsolidated Equity Investments

Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):



	2025	2024
ATC Holdings	($14)	($12)


Other	1	(3)
	($13)	($15)

Common Equity (Tables)

3 Months Ended

Mar. 31, 2025

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, 2025			256,690,222


Shareowner Direct Plan			99,700
Equity-based compensation plans			86,377

Shares outstanding, March 31, 2025			256,876,299

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

IPL [Member]

Schedule of Capitalization, Equity [Line Items]

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

WPL [Member]

Schedule of Capitalization, Equity [Line Items]

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):



Alliant Energy				Accumulated	Shares in
		Additional		Other	Deferred	Total
	Common	Paid-In	Retained	Comprehensive	Compensation	Common
	Stock	Capital	Earnings	Income (Loss)	Trust	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$3	$3,060	$3,954	$1	($14)	$7,004
Net income attributable to Alliant Energy common shareowners			213			213
Common stock dividends ($0.5075 per share)			(130)			(130)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other					1	1



Other comprehensive loss, net of tax				(1)		(1)
Ending balance, March 31, 2025	$3	$3,066	$4,037	$—	($13)	$7,093
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$3	$3,030	$3,756	$1	($13)	$6,777
Net income attributable to Alliant Energy common shareowners			158			158
Common stock dividends ($0.48 per share)			(123)			(123)
Shareowner Direct Plan issuances		6				6
Equity-based compensation plans and other		(3)			1	(2)



Other comprehensive income, net of tax				1		1
Ending balance, March 31, 2024	$3	$3,033	$3,791	$2	($12)	$6,817



IPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$33	$3,212	$1,216	$4,461
Net income			110	110
Common stock dividends			(89)	(89)
Capital contributions from parent		45		45
Ending balance, March 31, 2025	$33	$3,257	$1,237	$4,527
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$33	$2,887	$1,054	$3,974
Net income			63	63
Common stock dividends			(50)	(50)
Capital contributions from parent		50		50
Ending balance, March 31, 2024	$33	$2,937	$1,067	$4,037



WPL		Additional		Total
	Common	Paid-In	Retained	Common
	Stock	Capital	Earnings	Equity
Three Months Ended March 31, 2025
Beginning balance, December 31, 2024	$66	$2,533	$1,502	$4,101
Net income			110	110
Common stock dividends			(75)	(75)




Ending balance, March 31, 2025	$66	$2,533	$1,537	$4,136
Three Months Ended March 31, 2024
Beginning balance, December 31, 2023	$66	$2,478	$1,353	$3,897
Net income			92	92
Common stock dividends			(49)	(49)
Capital contributions from parent		55		55



Ending balance, March 31, 2024	$66	$2,533	$1,396	$3,995

Debt (Tables)

3 Months Ended

Mar. 31, 2025

Short-term Debt [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

IPL [Member]

Short-term Debt [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

WPL [Member]

Short-term Debt [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):


March 31, 2025	Alliant Energy	IPL	WPL
Amount outstanding	$678	$109	$212
Weighted average interest rates	4.6%	4.6%	4.6%
Available credit facility capacity (a)	$522	$141	$188


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Maximum amount outstanding (based on daily outstanding balances)	$678	$632	$127	$14	$224	$390
Average amount outstanding (based on daily outstanding balances)	$541	$487	$53	$1	$159	$255
Weighted average interest rates	4.5%	5.5%	4.6%	5.5%	4.5%	5.5%

(a)Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2025.

Revenues (Tables)

3 Months Ended

Mar. 31, 2025

Disaggregation of Revenue [Line Items]

Disaggregation of Revenue

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

IPL [Member]

Disaggregation of Revenue [Line Items]

Disaggregation of Revenue

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

WPL [Member]

Disaggregation of Revenue [Line Items]

Disaggregation of Revenue

Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):


	Alliant Energy		IPL		WPL
Three Months Ended March 31	2025	2024	2025	2024	2025	2024
Electric Utility:
Retail - residential	$323	$297	$155	$150	$168	$147
Retail - commercial	213	186	135	114	78	72
Retail - industrial	237	223	119	112	118	111
Wholesale	48	47	14	13	34	34
Bulk power and other	32	38	7	3	25	35
Total Electric Utility	853	791	430	392	423	399
Gas Utility:
Retail - residential	145	126	73	68	72	58
Retail - commercial	73	61	32	30	41	31
Retail - industrial	6	5	3	3	3	2
Transportation/other	16	13	10	7	6	6
Total Gas Utility	240	205	118	108	122	97
Other Utility:
Steam	10	12	10	12	—	—
Other utility	3	1	2	1	1	—
Total Other Utility	13	13	12	13	1	—
Non-Utility and Other:
Travero and other	22	22	—	—	—	—

Total Non-Utility and Other	22	22	—	—	—	—
Total revenues	$1,128	$1,031	$560	$513	$546	$496

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Income Taxes (Tables)

3 Months Ended

Mar. 31, 2025

Income Taxes [Line Items]

Schedule Of Effective Income Tax Rates

Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Summary Of Tax Credit Carryforwards

At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

IPL [Member]

Income Taxes [Line Items]

Schedule Of Effective Income Tax Rates

Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Summary Of Tax Credit Carryforwards

At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

WPL [Member]

Income Taxes [Line Items]

Schedule Of Effective Income Tax Rates

Overall effective income tax rates for the three months ended March 31, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Overall income tax rate	(28%)	(7%)		(57%)	(19%)	(5%)	6%

Summary Of Tax Credit Carryforwards

At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):


	Range of Expiration Dates	Alliant Energy	IPL	WPL

State net operating losses	2025-2045	$336	$7	$1
Federal tax credits	2033-2045	701	473	215

Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2025

Defined Benefit Plan Disclosure [Line Items]

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

Schedule Of Equity-based Compensation Plans Activity

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

Schedule Of Equity-based Compensation Plans Activity

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.


	Defined Benefit Pension Plans		OPEB Plans

Alliant Energy	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	11	11		2	2
Expected return on plan assets	(13)	(13)		(1)	(1)

Amortization of actuarial loss	6	6		—	—


	$5	$5		$1	$1


	Defined Benefit Pension Plans		OPEB Plans

IPL	2025	2024		2025	2024
Service cost	$1	$1		$—	$—
Interest cost	5	5		1	1
Expected return on plan assets	(6)	(7)		(1)	(1)

Amortization of actuarial loss	2	2		—	—
	$2	$1		$—	$—


	Defined Benefit Pension Plans		OPEB Plans

WPL	2025	2024		2025	2024

Interest cost	$5	$5		$1	$1
Expected return on plan assets	(6)	(6)		—	—

Amortization of actuarial loss	3	3		—	—

	$2	$2		$1	$1

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):


	Alliant Energy		IPL	WPL

	2025	2024		2025	2024	2025	2024
Compensation expense	$4	$4		$2	$2	$2	$2
Income tax benefits	1	1		1	1	—	—

Schedule Of Equity-based Compensation Plans Activity

For the three months ended March 31, 2025, 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)	78,689	$69.33
Performance shares (net income and environmental metrics)	89,930	61.62
Restricted stock units	82,641	61.62

Derivative Instruments (Tables)

3 Months Ended

Mar. 31, 2025

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

IPL [Member]

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

WPL [Member]

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of March 31, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and financial transmission rights (FTRs) that were accounted for as commodity derivative instruments were as follows (units in thousands; megawatt-hour (MWh); dekatherm (Dth)):


	Electricity		FTRs		Natural Gas		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years		Gallons	Years
Alliant Energy	1,883	2025-2026	4,080	2025	158,493	2025-2032		1,890	2025
IPL	544	2025-2026	1,432	2025	67,874	2025-2030		—	—
WPL	1,339	2025-2026	2,648	2025	90,619	2025-2032		1,890	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
	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024	March 31, 2025	December 31, 2024
Current derivative assets	$44	$41	$26	$29	$18	$12
Non-current derivative assets	26	34	14	19	12	15
Current derivative liabilities	16	26	6	11	10	15
Non-current derivative liabilities	36	32	4	2	32	30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):


	Alliant Energy		IPL		WPL
	Gross		Gross		Gross
	(as reported)	Net	(as reported)	Net	(as reported)	Net
March 31, 2025
Derivative assets	$70	$59	$40	$35	$30	$24
Derivative liabilities	52	41	10	5	42	36
December 31, 2024
Derivative assets	75	64	48	43	27	21
Derivative liabilities	58	47	13	8	45	39

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2025

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

Fair Value Measurements Using Significant Unobservable Inputs

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

IPL [Member]

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

Fair Value Measurements Using Significant Unobservable Inputs

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

WPL [Member]

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):


Alliant Energy	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$52	$52	$—	$—	$52
Commodity derivatives	70	—	59	11	70	75	—	48	27	75
Interest rate derivatives	—	—	—	—	—	1	—	1	—	1
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	52	—	50	2	52	58	—	56	2	58

Long-term debt (incl. current maturities)	9,951	—	9,526	—	9,526	9,848	—	9,577	—	9,577


IPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$9	$9	$—	$—	$9
Commodity derivatives	40	—	29	11	40	48	—	26	22	48
Deferred proceeds	86	—	—	86	86	163	—	—	163	163
Liabilities:
Commodity derivatives	10	—	8	2	10	13	—	11	2	13
Long-term debt (incl. current maturities)	4,191	—	3,891	—	3,891	4,090	—	3,736	—	3,736


WPL	March 31, 2025					December 31, 2024
		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	$—	$—	$—	$—	$—	$43	$43	$—	$—	$43
Commodity derivatives	30	—	30	—	30	27	—	22	5	27
Liabilities:
Commodity derivatives	42	—	42	—	42	45	—	45	—	45
Long-term debt	3,371	—	3,221	—	3,221	3,370	—	3,170	—	3,170

Fair Value Measurements Using Significant Unobservable Inputs

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


Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$25	$24	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	(2)	(3)	—	—




Settlements (a)	(14)	(14)	(77)	(32)
Ending balance, March 31	$9	$7	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($2)	($3)	$—	$—


IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2025	2024	2025	2024
Beginning balance, January 1	$20	$19	$163	$216
Total net losses included in changes in net assets (realized/unrealized)	—	(4)	—	—




Settlements (a)	(11)	(10)	(77)	(32)
Ending balance, March 31	$9	$5	$86	$184
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	$—	($4)	$—	$—


WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2025	2024
Beginning balance, January 1	$5	$5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1




Settlements	(3)	(4)
Ending balance, March 31	$—	$2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	($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 FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):


	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2025	($1)	$10	($1)	$10	$—	$—
December 31, 2024	—	25	—	20	—	5

- Definition

Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.

+ References + Details

Commitments And Contingencies (Tables)

3 Months Ended

Mar. 31, 2025

Commitments and Contingencies [Line Items]

Other Purchase Commitments

At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

MGP Site Estimated Future Costs And Recorded Liabilities

At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

IPL [Member]

Commitments and Contingencies [Line Items]

Other Purchase Commitments

At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

MGP Site Estimated Future Costs And Recorded Liabilities

At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

WPL [Member]

Commitments and Contingencies [Line Items]

Other Purchase Commitments

At March 31, 2025, 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	$872	$500	$372
Coal	112	62	50

Other (a)	130	59	33
	$1,114	$621	$455

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2025.

MGP Site Estimated Future Costs And Recorded Liabilities

At March 31, 2025, 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	-	$30	$6	-	$19	$2	-	$11
Current and non-current environmental liabilities	$13			$8			$5

Segments Of Business (Tables)

3 Months Ended

Mar. 31, 2025

Segment Reporting Information [Line Items]

Schedule Of Segments Of Business

Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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 reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

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 reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):


	Utility
			Total		Alliant
			Reportable		Energy
Three Months Ended March 31, 2025	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$430	$423	$853	N/A	$853
Gas utility revenues	118	122	240	N/A	240
Other revenues	12	1	13	$22	35
Total revenues	560	546	1,106	22	1,128
Electric production fuel and purchased power expense	67	108	175	N/A	175
Electric transmission service expense	108	50	158	N/A	158
Cost of gas sold expense	65	72	137	N/A	137

Other operation and maintenance expense	82	67	149	11	160
Other segment items:
Depreciation and amortization expense	115	93	208	3	211
Interest expense	47	43	90	29	119
Equity income from unconsolidated investments, net	—	—	—	(13)	(13)
Income tax benefit	(40)	(5)	(45)	(2)	(47)
Other (a)	6	8	14	1	15
Net income (loss)	110	110	220	(7)	213
Total assets	11,540	10,101	21,641	1,210	22,851
Investments in equity method subsidiaries	5	17	22	611	633
Construction and acquisition expenditures	376	178	554	28	582


	Utility
			Total		Alliant
Three Months Ended March 31, 2024 (amounts may not foot due to rounding)			Reportable		Energy
	IPL	WPL	Segments	Other	Consolidated
Electric utility revenues	$392	$399	$791	N/A	$791
Gas utility revenues	108	97	205	N/A	205
Other revenues	13	—	13	$22	35
Total revenues	513	496	1,009	22	1,031
Electric production fuel and purchased power expense	67	96	163	N/A	163
Electric transmission service expense	103	49	152	N/A	152
Cost of gas sold expense	60	53	113	N/A	114

Other operation and maintenance expense	86	63	149	11	160
Other segment items:
Depreciation and amortization expense	96	90	186	3	189
Interest expense	42	41	83	24	107
Equity income from unconsolidated investments, net	—	—	—	(15)	(15)
Income tax expense (benefit)	(10)	6	(4)	(6)	(10)
Other (a)	6	6	12	2	13
Net income	63	92	155	3	158
Total assets	10,532	9,581	20,113	1,135	21,248
Investments in equity method subsidiaries	5	16	21	573	594
Construction and acquisition expenditures	253	225	478	32	510

(a)Other segment items for each reportable segment include allowance for funds used during construction, taxes other than income taxes, interest income, and other miscellaneous income and deductions.

Related Parties (Tables)

3 Months Ended

Mar. 31, 2025

Services Provided, Sales Credited And Purchases

The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net Intercompany Payables

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

Related Amounts Billed Between Parties

The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):



	2025	2024
ATC billings to WPL	$38	$37
WPL billings to ATC	6	3

IPL [Member]

Services Provided, Sales Credited And Purchases

The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net Intercompany Payables

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

WPL [Member]

Services Provided, Sales Credited And Purchases

The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):


	IPL		WPL

	2025	2024		2025	2024
Corporate Services billings	$47	$43		$47	$40
Sales credited	1	—		22	22
Purchases billed	93	96		19	7

Net Intercompany Payables

Net intercompany payables to Corporate Services were as follows (in millions):

IPL

WPL

March 31, 2025

December 31, 2024

March 31, 2025

December 31, 2024

Net payables to Corporate Services

$125

$135

$74

$64

Related Amounts Billed Between Parties

The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):



	2025	2024
ATC billings to WPL	$38	$37
WPL billings to ATC	6	3

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Regulatory Assets [Line Items]
Regulatory assets	$ 2,274	$ 2,274
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,011	989
Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	414	401
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	312	315
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	173	180
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	56	68
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	60
Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	51
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	41	42
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	161	168
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,593	1,586
IPL [Member] \| Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	884	870
IPL [Member] \| Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	289	281
IPL [Member] \| Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	156	157
IPL [Member] \| Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	162	168
IPL [Member] \| Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	2	2
IPL [Member] \| Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	11	15
IPL [Member] \| Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	20	19
IPL [Member] \| Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	69	74
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	681	688
WPL [Member] \| Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	127	119
WPL [Member] \| Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	125	120
WPL [Member] \| Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	156	158
WPL [Member] \| Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	11	12
WPL [Member] \| Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	66
WPL [Member] \| Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	45
WPL [Member] \| Non-service pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	33	32
WPL [Member] \| WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	41	42
WPL [Member] \| Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 92	$ 94

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,083	$ 1,028
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	595	582
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	341	347
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	61	53
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	17
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	46	29
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	561	546
IPL [Member] \| Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	276	286
IPL [Member] \| Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	201	205
IPL [Member] \| Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	31	29
IPL [Member] \| Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27	12
IPL [Member] \| Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26	14
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	522	482
WPL [Member] \| Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	319	296
WPL [Member] \| Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	140	142
WPL [Member] \| Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30	24
WPL [Member] \| Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	13	5
WPL [Member] \| Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 20	$ 15

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Mar. 31, 2025 USD ($)
Receivables [Line Items]
Available capacity	$ 0
Financial Asset, Past Due [Member]
Receivables [Line Items]
Outstanding receivables past due	$ 27

- Definition

Amortized cost, before allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-13

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-7A

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 29
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-29

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (1)
-Publisher SEC

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph a
-Publisher SEC

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 80
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479294/326-20-55-80

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 79
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479294/326-20-55-79

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-14

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - Receivables Sold [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Maximum [Member]
Receivables [Line Items]
Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 110	$ 79
Average [Member]
Receivables [Line Items]
Average outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 108	$ 24

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Receivables [Line Items]
Fair value of deferred proceeds	$ 86	$ 163
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	86	163
Receivables Sold [Member] \| IPL [Member]
Receivables [Line Items]
Customer accounts receivable	139	137
Unbilled utility revenues	72	108
Receivables sold to third party	211	245
Less: cash proceeds	110	70
Deferred proceeds	101	175
Less: allowance for expected credit losses	15	12
Fair value of deferred proceeds	$ 86	$ 163

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - Receivables Sold [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Receivables [Line Items]
Collections	$ 607	$ 557
Write-offs, net of recoveries	$ 3	$ 3

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (13)	$ (15)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(14)	(12)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	1	(3)
Total [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (13)	$ (15)

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References + Details

Common Equity (Common Share Activity) (Details)	3 Months Ended
Common Equity (Common Share Activity) (Details)	Mar. 31, 2025 shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2025 (in shares)	256,690,222
Shareowner Direct Plan (in shares)	99,700
Equity-based compensation plans (in shares)	86,377
Shares outstanding, March 31, 2025 (in shares)	256,876,299

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 7,004
Beginning balance	7,004	$ 6,777
Net income attributable to common shareowners	213	158
Net income	213	158
Common stock dividends	(130)	(123)
Shareowner Direct Plan issuances	6	6
Equity-based compensation plans and other	1	(2)
Other comprehensive income (loss), net of tax	(1)	1
Ending balance	7,093
Ending balance	$ 7,093	$ 6,817
Common stock dividends (in dollars per share)	$ 0.5075	$ 0.48
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 3
Ending balance	3	3
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,060	3,030
Shareowner Direct Plan issuances	6	6
Equity-based compensation plans and other		(3)
Ending balance	3,066	3,033
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,954	3,756
Net income attributable to common shareowners	213	158
Common stock dividends	(130)	(123)
Ending balance	4,037	3,791
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1	1
Other comprehensive income (loss), net of tax	(1)	1
Ending balance	0	2
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(14)	(13)
Equity-based compensation plans and other	1	1
Ending balance	(13)	(12)
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	4,461
Beginning balance	4,461	3,974
Net income attributable to common shareowners	110	63
Net income	110	63
Common stock dividends	(89)	(50)
Capital contributions from parent	45	50
Ending balance	4,527
Ending balance	4,527	4,037
IPL [Member] \| Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33
Ending balance	33	33
IPL [Member] \| Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,212	2,887
Capital contributions from parent	45	50
Ending balance	3,257	2,937
IPL [Member] \| Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,216	1,054
Net income	110	63
Common stock dividends	(89)	(50)
Ending balance	1,237	1,067
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	4,101
Beginning balance	4,101	3,897
Net income attributable to common shareowners	110	92
Net income	110	92
Common stock dividends	(75)	(49)
Capital contributions from parent	0	55
Ending balance	4,136
Ending balance	4,136	3,995
WPL [Member] \| Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66
Ending balance	66	66
WPL [Member] \| Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,533	2,478
Capital contributions from parent		55
Ending balance	2,533	2,533
WPL [Member] \| Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,502	1,353
Net income	110	92
Common stock dividends	(75)	(49)
Ending balance	$ 1,537	$ 1,396

Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2026	Dec. 31, 2024
Debt [Line Items]
Line of credit facility, current borrowing capacity		$ 1,300
Payments to retire long-term debt		0	$ 300
Long-term debt, fair value		9,526			$ 9,577
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		550
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		350
Long-term debt, fair value		3,891			3,736
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		400
Long-term debt, fair value		3,221			$ 3,170
Term Loan Credit Agreement [Member] \| Term loan credit agreement through March 2026 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt		$ 300
Interest rate, percent		5.00%
Term Loan Credit Agreement [Member] \| Term loan credit agreement through March 2026 [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 2025 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Payments to retire long-term debt		$ 300
Long-Term Commercial Paper [Member]
Debt [Line Items]
Long-term commercial paper		$ 100
Long-term commercial paper interest rate, percent		4.60%
Long-Term Commercial Paper [Member] \| Subsequent Event [Member]
Debt [Line Items]
Increase in long-term commercial paper	$ 50
Long-Term Commercial Paper [Member] \| IPL [Member]
Debt [Line Items]
Long-term commercial paper		$ 100
Long-term commercial paper interest rate, percent		4.60%
Long-Term Commercial Paper [Member] \| IPL [Member] \| Subsequent Event [Member]
Debt [Line Items]
Increase in long-term commercial paper	$ 50
Convertible Senior Notes [Member] \| 3.875% convertible senior notes, due 2026 [Member]
Debt [Line Items]
Long-term debt, carrying value		$ 572
Unamortized debt issuance costs		3
Long-term debt, fair value		$ 617
Shares included in diluted earnings per share (in shares)		0

Debt (Credit Facilities) (Details) $ in Millions	Mar. 31, 2025 USD ($)
Debt [Line Items]
Amount outstanding	$ 678
Weighted average interest rates	4.60%
Available credit facility capacity	$ 522
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 109
Weighted average interest rates	4.60%
Available credit facility capacity	$ 141
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 212
Weighted average interest rates	4.60%
Available credit facility capacity	$ 188

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 26: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 27: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

+ Details

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 678	$ 632
Average amount outstanding (based on daily outstanding balances)	$ 541	$ 487
Weighted average interest rates	4.50%	5.50%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 127	$ 14
Average amount outstanding (based on daily outstanding balances)	$ 53	$ 1
Weighted average interest rates	4.60%	5.50%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 224	$ 390
Average amount outstanding (based on daily outstanding balances)	$ 159	$ 255
Weighted average interest rates	4.50%	5.50%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482949/835-30-55-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69F

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1D

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 26: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 27: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482900/835-30-50-1

+ Details

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,128	$ 1,031
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	853	791
Electric [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	323	297
Electric [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	213	186
Electric [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	237	223
Electric [Member] \| Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48	47
Electric [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32	38
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	240	205
Gas [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	145	126
Gas [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	61
Gas [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	5
Gas [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	13
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	13
Other Utility [Member] \| Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	12
Other Utility [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	1
Non-Utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	22
Non-Utility and Other [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	22
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	560	513
IPL [Member] \| Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	430	392
IPL [Member] \| Electric [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	155	150
IPL [Member] \| Electric [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	135	114
IPL [Member] \| Electric [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	119	112
IPL [Member] \| Electric [Member] \| Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	13
IPL [Member] \| Electric [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	3
IPL [Member] \| Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118	108
IPL [Member] \| Gas [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	68
IPL [Member] \| Gas [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32	30
IPL [Member] \| Gas [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	3
IPL [Member] \| Gas [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	7
IPL [Member] \| Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	13
IPL [Member] \| Other Utility [Member] \| Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	12
IPL [Member] \| Other Utility [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	546	496
WPL [Member] \| Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	423	399
WPL [Member] \| Electric [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	168	147
WPL [Member] \| Electric [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	78	72
WPL [Member] \| Electric [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118	111
WPL [Member] \| Electric [Member] \| Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34	34
WPL [Member] \| Electric [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25	35
WPL [Member] \| Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	122	97
WPL [Member] \| Gas [Member] \| Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72	58
WPL [Member] \| Gas [Member] \| Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	41	31
WPL [Member] \| Gas [Member] \| Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2
WPL [Member] \| Gas [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	6
WPL [Member] \| Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0
WPL [Member] \| Other Utility [Member] \| Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1	$ 0

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Effective Tax Rate [Line Items]
Overall income tax rate	(28.00%)	(7.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(57.00%)	(19.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(5.00%)	6.00%

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2025 USD ($)
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 336
Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	701
IPL [Member] \| State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	7
IPL [Member] \| Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	473
WPL [Member] \| State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
WPL [Member] \| Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	$ 215

Benefit Plans (Narrative) (Details) $ in Millions	3 Months Ended
Benefit Plans (Narrative) (Details) $ in Millions	Mar. 31, 2025 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 22
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 11
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 10
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) \| shares	408,289

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1
Interest cost	11	11
Expected return on plan assets	(13)	(13)
Amortization of actuarial loss	6	6
Total	5	5
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	2	2
Expected return on plan assets	(1)	(1)
Amortization of actuarial loss	0	0
Total	1	1
IPL [Member] \| Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	5	5
Expected return on plan assets	(6)	(7)
Amortization of actuarial loss	2	2
Total	2	1
IPL [Member] \| OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	(1)	(1)
Amortization of actuarial loss	0	0
Total	0	0
WPL [Member] \| Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	5	5
Expected return on plan assets	(6)	(6)
Amortization of actuarial loss	3	3
Total	2	2
WPL [Member] \| OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Expected return on plan assets	0	0
Amortization of actuarial loss	0	0
Total	$ 1	$ 1

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Compensation expense	$ 4	$ 4
Income tax benefits	1	1
IPL [Member]
Compensation expense	2	2
Income tax benefits	1	1
WPL [Member]
Compensation expense	2	2
Income tax benefits	$ 0	$ 0

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	3 Months Ended
	Mar. 31, 2025 $ / 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	78,689
Weighted average grant date fair value (in dollars per share/unit) \| $ / shares	$ 69.33
Performance Shares (net income and environmental metrics) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) \| shares	89,930
Weighted average grant date fair value (in dollars per share/unit) \| $ / shares	$ 61.62
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) \| shares	82,641
Weighted average grant date fair value (in dollars per share/unit) \| $ / shares	$ 61.62

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity Contracts [Member] gal in Thousands	3 Months Ended
	Mar. 31, 2025 Dekatherms MWh gal
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,883
Electricity (MWhs) [Member] \| IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	544
Electricity (MWhs) [Member] \| WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,339
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	4,080
FTRs (MWhs) [Member] \| IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,432
FTRs (MWhs) [Member] \| WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	2,648
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) \| Dekatherms	158,493
Natural Gas (Dths) [Member] \| IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) \| Dekatherms	67,874
Natural Gas (Dths) [Member] \| WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) \| Dekatherms	90,619
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) \| gal	1,890
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	1,890

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 44	$ 41
Non-current derivative assets	26	34
Current derivative liabilities	16	26
Non-current derivative liabilities	36	32
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	26	29
Non-current derivative assets	14	19
Current derivative liabilities	6	11
Non-current derivative liabilities	4	2
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	18	12
Non-current derivative assets	12	15
Current derivative liabilities	10	15
Non-current derivative liabilities	$ 32	$ 30

Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$ 70	$ 75
Derivative assets, Net	59	64
Derivative liabilities, Gross (as reported)	52	58
Derivative liabilities, Net	41	47
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	40	48
Derivative assets, Net	35	43
Derivative liabilities, Gross (as reported)	10	13
Derivative liabilities, Net	5	8
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	30	27
Derivative assets, Net	24	21
Derivative liabilities, Gross (as reported)	42	45
Derivative liabilities, Net	$ 36	$ 39

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Carrying Amount [Member]
Assets:
Money market fund investments	$ 0	$ 52
Deferred proceeds	86	163
Liabilities:
Long-term debt (incl. current maturities)	9,951	9,848
Carrying Amount [Member] \| IPL [Member]
Assets:
Money market fund investments	0	9
Deferred proceeds	86	163
Liabilities:
Long-term debt (incl. current maturities)	4,191	4,090
Carrying Amount [Member] \| WPL [Member]
Assets:
Money market fund investments	0	43
Liabilities:
Long-term debt (incl. current maturities)	3,371	3,370
Carrying Amount [Member] \| Commodity Contracts [Member]
Assets:
Derivatives	70	75
Liabilities:
Derivatives	52	58
Carrying Amount [Member] \| Commodity Contracts [Member] \| IPL [Member]
Assets:
Derivatives	40	48
Liabilities:
Derivatives	10	13
Carrying Amount [Member] \| Commodity Contracts [Member] \| WPL [Member]
Assets:
Derivatives	30	27
Liabilities:
Derivatives	42	45
Carrying Amount [Member] \| Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Money market fund investments	0	52
Deferred proceeds	86	163
Liabilities:
Long-term debt (incl. current maturities)	9,526	9,577
IPL [Member]
Assets:
Money market fund investments	0	9
Deferred proceeds	86	163
Liabilities:
Long-term debt (incl. current maturities)	3,891	3,736
WPL [Member]
Assets:
Money market fund investments	0	43
Liabilities:
Long-term debt (incl. current maturities)	3,221	3,170
Commodity Contracts [Member]
Assets:
Derivatives	70	75
Liabilities:
Derivatives	52	58
Commodity Contracts [Member] \| IPL [Member]
Assets:
Derivatives	40	48
Liabilities:
Derivatives	10	13
Commodity Contracts [Member] \| WPL [Member]
Assets:
Derivatives	30	27
Liabilities:
Derivatives	42	45
Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Level 1 [Member]
Assets:
Money market fund investments	0	52
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] \| IPL [Member]
Assets:
Money market fund investments	0	9
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] \| WPL [Member]
Assets:
Money market fund investments	0	43
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)	9,526	9,577
Level 2 [Member] \| IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,891	3,736
Level 2 [Member] \| WPL [Member]
Assets:
Money market fund investments	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,221	3,170
Level 2 [Member] \| Commodity Contracts [Member]
Assets:
Derivatives	59	48
Liabilities:
Derivatives	50	56
Level 2 [Member] \| Commodity Contracts [Member] \| IPL [Member]
Assets:
Derivatives	29	26
Liabilities:
Derivatives	8	11
Level 2 [Member] \| Commodity Contracts [Member] \| WPL [Member]
Assets:
Derivatives	30	22
Liabilities:
Derivatives	42	45
Level 2 [Member] \| Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	86	163
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] \| IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	86	163
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	11	27
Liabilities:
Derivatives	2	2
Level 3 [Member] \| Commodity Contracts [Member] \| IPL [Member]
Assets:
Derivatives	11	22
Liabilities:
Derivatives	2	2
Level 3 [Member] \| Commodity Contracts [Member] \| WPL [Member]
Assets:
Derivatives	0	5
Liabilities:
Derivatives	0	0
Level 3 [Member] \| Interest Rate Swap [Member]
Assets:
Derivatives	$ 0	$ 0

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 25	$ 24
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	(3)
Settlements	(14)	(14)
Ending balance	9	7
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	(2)	(3)
Commodity Contracts [Member] \| IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	20	19
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	(4)
Settlements	(11)	(10)
Ending balance	9	5
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	0	(4)
Commodity Contracts [Member] \| WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5	5
Total net gains (losses) included in changes in net assets (realized/unrealized)	(2)	1
Settlements	(3)	(4)
Ending balance	0	2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	(2)	1
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	163	216
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Settlements	(77)	(32)
Ending balance	86	184
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	0	0
Deferred Proceeds [Member] \| IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	163	216
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Settlements	(77)	(32)
Ending balance	86	184
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at March 31	$ 0	$ 0

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 9	$ 25	$ 7	$ 24
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets		0
Fair value, net derivative liabilities	(1)
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	10	25
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	9	20	5	19
IPL [Member] \| Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets		0
Fair value, net derivative liabilities	(1)
IPL [Member] \| Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	10	20
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	0	5	$ 2	$ 5
WPL [Member] \| Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	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	$ 0	$ 5

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,114
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	621
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	455
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	$ 43
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent	6.00%
Obligations, maximum	$ 54
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	301
Capital Purchase Commitment [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	136
Capital Purchase Commitment [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	163
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	193
Renewable Tax Credits Transferred [Member] \| Indemnification Agreement [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	121
Reimbursement of Transmission Construction Costs [Member] \| Indemnification Agreement [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	6
Reimbursement of Transmission Construction Costs [Member] \| Indemnification Agreement [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	$ 15

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,114
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	621
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	455
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	872
Natural gas [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	500
Natural gas [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	372
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	112
Coal [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	62
Coal [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	50
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	130
Other [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	59
Other [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 33

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	3 Months Ended
	Mar. 31, 2025 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	30
Maximum [Member] \| IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	19
Maximum [Member] \| WPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 11

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Segment Reporting Information [Line Items]
Electric utility revenues	$ 853	$ 791
Gas utility revenues	240	205
Other revenues	35	35
Total revenues	1,128	1,031
Electric production fuel and purchased power	175	163
Electric transmission service	158	152
Cost of gas sold	137	114
Other operation and maintenance	160	160
Depreciation and amortization	211	189
Interest expense	119	107
Equity income from unconsolidated investments, net	(13)	(15)
Income tax expense (benefit)	(47)	(10)
Other	15	13
Net income (loss)	213	158
Total assets	22,851	21,248	$ 22,714
Investments in equity method subsidiaries	633	594
Construction and acquisition expenditures	582	510
IPL [Member]
Segment Reporting Information [Line Items]
Electric utility revenues	430	392
Gas utility revenues	118	108
Total revenues	560	513
Electric production fuel and purchased power	67	67
Electric transmission service	108	103
Cost of gas sold	65	60
Depreciation and amortization	115	96
Income tax expense (benefit)	(40)	(10)
Net income (loss)	110	63
Total assets	11,540		11,407
WPL [Member]
Segment Reporting Information [Line Items]
Electric utility revenues	423	399
Gas utility revenues	122	97
Total revenues	546	496
Electric production fuel and purchased power	108	96
Electric transmission service	50	49
Cost of gas sold	72	53
Depreciation and amortization	93	90
Income tax expense (benefit)	(5)	6
Net income (loss)	110	92
Total assets	10,101		$ 10,106
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Electric utility revenues	853	791
Gas utility revenues	240	205
Other revenues	13	13
Total revenues	1,106	1,009
Electric production fuel and purchased power	175	163
Electric transmission service	158	152
Cost of gas sold	137	113
Other operation and maintenance	149	149
Depreciation and amortization	208	186
Interest expense	90	83
Equity income from unconsolidated investments, net	0	0
Income tax expense (benefit)	(45)	(4)
Other	14	12
Net income (loss)	220	155
Total assets	21,641	20,113
Investments in equity method subsidiaries	22	21
Construction and acquisition expenditures	554	478
IPL [Member]
Segment Reporting Information [Line Items]
Electric utility revenues	430	392
Gas utility revenues	118	108
Other revenues	12	13
Total revenues	560	513
Electric production fuel and purchased power	67	67
Electric transmission service	108	103
Cost of gas sold	65	60
Other operation and maintenance	82	86
Depreciation and amortization	115	96
Interest expense	47	42
Equity income from unconsolidated investments, net	0	0
Income tax expense (benefit)	(40)	(10)
Other	6	6
Net income (loss)	110	63
Total assets	11,540	10,532
Investments in equity method subsidiaries	5	5
Construction and acquisition expenditures	376	253
WPL [Member]
Segment Reporting Information [Line Items]
Electric utility revenues	423	399
Gas utility revenues	122	97
Other revenues	1	0
Total revenues	546	496
Electric production fuel and purchased power	108	96
Electric transmission service	50	49
Cost of gas sold	72	53
Other operation and maintenance	67	63
Depreciation and amortization	93	90
Interest expense	43	41
Equity income from unconsolidated investments, net	0	0
Income tax expense (benefit)	(5)	6
Other	8	6
Net income (loss)	110	92
Total assets	10,101	9,581
Investments in equity method subsidiaries	17	16
Construction and acquisition expenditures	178	225
Other [Member]
Segment Reporting Information [Line Items]
Other revenues	22	22
Total revenues	22	22
Other operation and maintenance	11	11
Depreciation and amortization	3	3
Interest expense	29	24
Equity income from unconsolidated investments, net	(13)	(15)
Income tax expense (benefit)	(2)	(6)
Other	1	2
Net income (loss)	(7)	3
Total assets	1,210	1,135
Investments in equity method subsidiaries	611	573
Construction and acquisition expenditures	$ 28	$ 32

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
WPL [Member] \| ATC LLC [Member] \| WPL Owed ATC LLC [Member] \| Related Party [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 10	$ 10

- Definition

Amount of liabilities classified as other.

+ References + Details

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Corporate Services Billings [Member] \| IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 47	$ 43
Corporate Services Billings [Member] \| WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	47	40
Sales Credited [Member] \| IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	1	0
Sales Credited [Member] \| WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	22	22
Purchases Billed [Member] \| IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	93	96
Purchases Billed [Member] \| WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 19	$ 7

Related Parties (Net Intercompany Payables) (Details) - Related Party [Member] - Corporate Services [Member] - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 125	$ 135
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 74	$ 64

- Definition

Amount of liabilities classified as other.

+ References + Details

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - WPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 38	$ 37
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 6	$ 3