Interstate Power & Light (IPLDP) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	3 Months Ended
	Mar. 31, 2021shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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	250,134,552
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
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
Title of 12(b) Security	5.100% Series D Cumulative Perpetual Preferred Stock, $0.01 Par Value
Trading Symbol	IPLDP
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Information [Line Items]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	0-337
Entity Tax Identification Number	39-0714890
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Electric utility	$ 701	$ 730
Gas utility	170	152
Other utility	13	12
Non-utility	17	22
Total revenues	901	916
Operating expenses:
Electric production fuel and purchased power	133	184
Electric transmission service	134	122
Cost of gas sold	100	85
Other operation and maintenance	146	163
Depreciation and amortization	164	146
Taxes other than income taxes	26	28
Total operating expenses	703	728
Operating income	198	188
Other (income) and deductions:
Interest expense	69	69
Equity income from unconsolidated investments, net	(15)	(13)
Allowance for funds used during construction	(4)	(23)
Other	2	1
Total other (income) and deductions	52	34
Income before income taxes	146	154
Income tax benefit	(28)	(19)
Net income	174	173
Preferred dividend requirements of Interstate Power and Light Company	3	3
Net income attributable to common shareowners	$ 171	$ 170
Weighted average number of common shares outstanding:
Basic (in shares)	250	244.4
Diluted (in shares)	250.4	244.6
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted)	$ 0.68	$ 0.70
IPL [Member]
Revenues:
Electric utility	$ 386	$ 425
Gas utility	91	83
Other utility	12	11
Total revenues	489	519
Operating expenses:
Electric production fuel and purchased power	59	106
Electric transmission service	92	84
Cost of gas sold	50	44
Other operation and maintenance	77	87
Depreciation and amortization	94	86
Taxes other than income taxes	14	15
Total operating expenses	386	422
Operating income	103	97
Other (income) and deductions:
Interest expense	35	34
Allowance for funds used during construction	(2)	(10)
Other	0	1
Total other (income) and deductions	33	25
Income before income taxes	70	72
Income tax benefit	(12)	(14)
Net income	82	86
Preferred dividend requirements of Interstate Power and Light Company	3	3
Net income attributable to common shareowners	79	83
WPL [Member]
Revenues:
Electric utility	315	305
Gas utility	79	69
Other utility	1	1
Total revenues	395	375
Operating expenses:
Electric production fuel and purchased power	74	78
Electric transmission service	42	38
Cost of gas sold	50	41
Other operation and maintenance	59	54
Depreciation and amortization	69	59
Taxes other than income taxes	11	11
Total operating expenses	305	281
Operating income	90	94
Other (income) and deductions:
Interest expense	26	25
Allowance for funds used during construction	(2)	(13)
Other	1	0
Total other (income) and deductions	25	12
Income before income taxes	65	82
Income tax benefit	(19)	(8)
Net income	$ 84	$ 90

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 14	$ 54
Accounts receivable, less allowance for expected credit losses	325	412
Production fuel, at weighted average cost	57	66
Gas stored underground, at weighted average cost	25	46
Materials and supplies, at weighted average cost	122	105
Regulatory assets	95	81
Other	117	123
Total current assets	755	887
Property, plant and equipment, net	14,353	14,336
Investments:
ATC Holdings	334	331
Other	160	154
Total investments	494	485
Other assets:
Regulatory assets	1,912	1,929
Deferred charges and other	80	73
Total other assets	1,992	2,002
Total assets	17,594	17,710
Current liabilities:
Current maturities of long-term debt	308	8
Commercial paper	336	389
Accounts payable	307	377
Regulatory liabilities	208	249
Other	249	274
Total current liabilities	1,408	1,297
Long-term debt, net (excluding current portion)	6,471	6,769
Other liabilities:
Deferred tax liabilities	1,843	1,814
Regulatory liabilities	1,047	1,057
Pension and other benefit obligations	495	511
Other	364	374
Total other liabilities	3,749	3,756
Commitments and contingencies (Note 12)
Common equity:
Common stock	3	2
Additional paid-in capital	2,712	2,704
Retained earnings	3,063	2,994
Accumulated other comprehensive loss	(1)	(1)
Shares in deferred compensation trust - 365,523 and 380,542 shares at a weighted average cost of $29.17 and $28.73 per share	(11)	(11)
Total common equity	5,766	5,688
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	5,966	5,888
Total liabilities and equity	17,594	17,710
IPL [Member]
Current assets:
Cash and cash equivalents	11	50
Accounts receivable, less allowance for expected credit losses	130	210
Production fuel, at weighted average cost	45	48
Gas stored underground, at weighted average cost	8	20
Materials and supplies, at weighted average cost	73	63
Regulatory assets	73	52
Other	53	53
Total current assets	393	496
Property, plant and equipment, net	7,872	7,889
Other assets:
Regulatory assets	1,421	1,431
Deferred charges and other	40	33
Total other assets	1,461	1,464
Total assets	9,726	9,849
Current liabilities:
Accounts payable	119	162
Accounts payable to associated companies	0	45
Regulatory liabilities	87	103
Other	131	137
Total current liabilities	337	447
Long-term debt, net (excluding current portion)	3,346	3,345
Other liabilities:
Deferred tax liabilities	1,047	1,035
Regulatory liabilities	574	573
Pension and other benefit obligations	180	186
Other	300	299
Total other liabilities	2,101	2,093
Commitments and contingencies (Note 12)
Common equity:
Common stock	33	33
Additional paid-in capital	2,752	2,752
Retained earnings	957	979
Total common equity	3,742	3,764
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,942	3,964
Total liabilities and equity	9,726	9,849
WPL [Member]
Current assets:
Cash and cash equivalents	2	3
Accounts receivable, less allowance for expected credit losses	183	192
Production fuel, at weighted average cost	12	18
Gas stored underground, at weighted average cost	17	26
Materials and supplies, at weighted average cost	47	40
Regulatory assets	22	29
Other	47	54
Total current assets	330	362
Property, plant and equipment, net	6,053	6,022
Other assets:
Regulatory assets	491	498
Deferred charges and other	36	30
Total other assets	527	528
Total assets	6,910	6,912
Current liabilities:
Commercial paper	148	257
Accounts payable	125	154
Accounts payable to associated companies	17	35
Regulatory liabilities	121	146
Other	94	82
Total current liabilities	505	674
Long-term debt, net (excluding current portion)	2,131	2,130
Other liabilities:
Deferred tax liabilities	719	702
Regulatory liabilities	473	484
Finance lease obligations - Sheboygan Falls Energy Facility	39	42
Pension and other benefit obligations	215	222
Other	183	180
Total other liabilities	1,629	1,630
Commitments and contingencies (Note 12)
Common equity:
Common stock	66	66
Additional paid-in capital	1,584	1,459
Retained earnings	995	953
Total common equity	2,645	2,478
Total equity	2,645	2,478
Total liabilities and equity	$ 6,910	$ 6,912

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
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)	250,134,552	249,868,415
Shares in deferred compensation trust (in shares)	365,523	380,542
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 29.17	$ 28.73
IPL [Member]
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed Consolidated Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from (used for) operating activities:
Net income	$ 174	$ 173
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	164	146
Deferred tax benefit and tax credits	(29)	(23)
Other	4	5
Other changes in assets and liabilities:
Accounts receivable	(126)	(119)
Regulatory liabilities	(60)	(38)
Deferred income taxes	58	50
Pension and other benefit obligations	(16)	(31)
Other	(24)	(3)
Net cash flows from (used for) operating activities	145	160
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(214)	(278)
Other construction and acquisition expenditures	(17)	(11)
Cash receipts on sold receivables	209	123
Other	(16)	(13)
Net cash flows from (used for) investing activities	(38)	(179)
Cash flows from (used for) financing activities:
Common stock dividends	(102)	(93)
Proceeds from issuance of common stock, net	8	228
Proceeds from issuance of long-term debt	0	300
Payments to retire long-term debt	0	(300)
Net change in commercial paper and other short-term borrowings	(53)	(67)
Other	2	(8)
Net cash flows from (used for) financing activities	(145)	60
Net increase (decrease) in cash, cash equivalents and restricted cash	(38)	41
Cash, cash equivalents and restricted cash at beginning of period	56	18
Cash, cash equivalents and restricted cash at end of period	18	59
Supplemental cash flows information:
Interest	(59)	(65)
Significant non-cash investing and financing activities:
Accrued capital expenditures	64	156
Beneficial interest obtained in exchange for securitized accounts receivable	107	188
IPL [Member]
Cash flows from (used for) operating activities:
Net income	82	86
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	94	86
Other	(3)	(15)
Other changes in assets and liabilities:
Accounts receivable	(133)	(126)
Regulatory assets	(16)	(9)
Regulatory liabilities	(19)	1
Deferred income taxes	14	15
Other	(64)	(13)
Net cash flows from (used for) operating activities	(45)	25
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(106)	(165)
Cash receipts on sold receivables	209	123
Other	(5)	(11)
Net cash flows from (used for) investing activities	98	(53)
Cash flows from (used for) financing activities:
Common stock dividends	(101)	(60)
Capital contributions from parent	0	100
Other	9	4
Net cash flows from (used for) financing activities	(92)	44
Net increase (decrease) in cash, cash equivalents and restricted cash	(39)	16
Cash, cash equivalents and restricted cash at beginning of period	50	9
Cash, cash equivalents and restricted cash at end of period	11	25
Supplemental cash flows information:
Interest	(37)	(41)
Income taxes, net	7	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	31	92
Beneficial interest obtained in exchange for securitized accounts receivable	107	188
WPL [Member]
Cash flows from (used for) operating activities:
Net income	84	90
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	69	59
Deferred tax benefit and tax credits	(28)	(11)
Other	4	(5)
Other changes in assets and liabilities:
Regulatory liabilities	(41)	(39)
Deferred income taxes	44	32
Other	16	22
Net cash flows from (used for) operating activities	148	148
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(108)	(113)
Other	(11)	(11)
Net cash flows from (used for) investing activities	(119)	(124)
Cash flows from (used for) financing activities:
Common stock dividends	(42)	(43)
Capital contributions from parent	125	25
Net change in commercial paper and other short-term borrowings	(109)	14
Other	(4)	(1)
Net cash flows from (used for) financing activities	(30)	(5)
Net increase (decrease) in cash, cash equivalents and restricted cash	(1)	19
Cash, cash equivalents and restricted cash at beginning of period	3	4
Cash, cash equivalents and restricted cash at end of period	2	23
Supplemental cash flows information:
Interest	(21)	(21)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 32	$ 62

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the 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 latest combined Annual Report on 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, 2021 are not necessarily indicative of results that may be expected for the year ending December 31, 2021. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the 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 latest combined Annual Report on 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, 2021 are not necessarily indicative of results that may be expected for the year ending December 31, 2021. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the 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 latest combined Annual Report on 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, 2021 are not necessarily indicative of results that may be expected for the year ending December 31, 2021. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2021
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.
IPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.
WPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.

Receivables

Receivables	3 Months Ended
	Mar. 31, 2021
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, 2021, IPL had $15 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding 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): 2021 2020 Maximum outstanding aggregate cash proceeds $100 $96 Average outstanding aggregate cash proceeds 30 24 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2021 December 31, 2020 Customer accounts receivable $124 $114 Unbilled utility revenues 74 92 Receivables sold to third party 198 206 Less: cash proceeds 75 1 Deferred proceeds 123 205 Less: allowance for expected credit losses 16 17 Fair value of deferred proceeds $107 $188 As of March 31, 2021, outstanding receivables past due under the Receivables Agreement were $22 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2021 2020 Collections $529 $541 Write-offs, net of recoveries 2 2 In April 2021, IPL amended and extended through March 2023 the purchase commitment from the third party to which it sells its receivables. Effective April 2021, the limit on cash proceeds is $110 million.
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of March 31, 2021, IPL had $15 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding 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): 2021 2020 Maximum outstanding aggregate cash proceeds $100 $96 Average outstanding aggregate cash proceeds 30 24 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2021 December 31, 2020 Customer accounts receivable $124 $114 Unbilled utility revenues 74 92 Receivables sold to third party 198 206 Less: cash proceeds 75 1 Deferred proceeds 123 205 Less: allowance for expected credit losses 16 17 Fair value of deferred proceeds $107 $188 As of March 31, 2021, outstanding receivables past due under the Receivables Agreement were $22 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2021 2020 Collections $529 $541 Write-offs, net of recoveries 2 2 In April 2021, IPL amended and extended through March 2023 the purchase commitment from the third party to which it sells its receivables. Effective April 2021, the limit on cash proceeds is $110 million.

Investments

Investments	3 Months Ended
	Mar. 31, 2021
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): 2021 2020 ATC Holdings ($11) ($11) Other (4) (2) ($15) ($13)

Common Equity

Common Equity	3 Months Ended
	Mar. 31, 2021
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, 2021 249,868,415 Shareowner Direct Plan 152,588 Equity-based compensation plans 113,549 Shares outstanding, March 31, 2021 250,134,552 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436
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, 2021 249,868,415 Shareowner Direct Plan 152,588 Equity-based compensation plans 113,549 Shares outstanding, March 31, 2021 250,134,552 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436
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, 2021 249,868,415 Shareowner Direct Plan 152,588 Equity-based compensation plans 113,549 Shares outstanding, March 31, 2021 250,134,552 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%
IPL [Member]
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%
WPL [Member]
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%

Revenues

Revenues	3 Months Ended
	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%) Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%) Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%) Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180

Benefit Plans

Benefit Plans	3 Months Ended
	Mar. 31, 2021
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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy. 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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — — As of March 31, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13 million, $7 million and $5 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, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of March 31, 2021, 425,849 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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy. 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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — — As of March 31, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13 million, $7 million and $5 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, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of March 31, 2021, 425,849 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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy. 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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — — As of March 31, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13 million, $7 million and $5 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, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of March 31, 2021, 425,849 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Derivative Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of March 31, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7 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 in the form of letters of credit or cash collateral 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, 2021 and December 31, 2020, 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at March 31, 2021 and December 31, 2020. 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, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7 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 in the form of letters of credit or cash collateral 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, 2021 and December 31, 2020, 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at March 31, 2021 and December 31, 2020. 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, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7 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 in the form of letters of credit or cash collateral 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, 2021 and December 31, 2020, 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at March 31, 2021 and December 31, 2020. Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (6) (3) — — Settlements (a) (7) (4) (81) — Ending balance, March 31 $16 $14 $107 $188 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 ($6) ($3) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (5) (2) — — Settlements (a) (6) (3) (81) — Ending balance, March 31 $15 $13 $107 $188 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 ($6) ($2) $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (6) (3) — — Settlements (a) (7) (4) (81) — Ending balance, March 31 $16 $14 $107 $188 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 ($6) ($3) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (5) (2) — — Settlements (a) (6) (3) (81) — Ending balance, March 31 $15 $13 $107 $188 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 ($6) ($2) $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (6) (3) — — Settlements (a) (7) (4) (81) — Ending balance, March 31 $16 $14 $107 $188 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 ($6) ($3) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (5) (2) — — Settlements (a) (6) (3) (81) — Ending balance, March 31 $15 $13 $107 $188 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 ($6) ($2) $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2021
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 WPL’s expansion of solar generation. At March 31, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $10 million and $10 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, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021. NOTE 12(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2021, the currently known partnership obligations for the abandonment obligations are estimated at $68 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $68 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, as of both March 31, 2021 and December 31, 2020, a liability of $5 million is recorded in “Other liabilities” on Alliant Energy’s balance sheets for expected credit losses related to the contingent obligations that are in the scope of these guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $74 million as of March 31, 2021 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, 2021 and December 31, 2020. 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, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $25 $7 - $19 Current and non-current environmental liabilities $13 $9 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 Burlington by December 31, 2021 and 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: 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 WPL’s expansion of solar generation. At March 31, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $10 million and $10 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, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021. NOTE 12(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2021, the currently known partnership obligations for the abandonment obligations are estimated at $68 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $68 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, as of both March 31, 2021 and December 31, 2020, a liability of $5 million is recorded in “Other liabilities” on Alliant Energy’s balance sheets for expected credit losses related to the contingent obligations that are in the scope of these guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $74 million as of March 31, 2021 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, 2021 and December 31, 2020. 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, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $25 $7 - $19 Current and non-current environmental liabilities $13 $9 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 Burlington by December 31, 2021 and 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: 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 WPL’s expansion of solar generation. At March 31, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $10 million and $10 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, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021. NOTE 12(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of March 31, 2021, the currently known partnership obligations for the abandonment obligations are estimated at $68 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $68 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, as of both March 31, 2021 and December 31, 2020, a liability of $5 million is recorded in “Other liabilities” on Alliant Energy’s balance sheets for expected credit losses related to the contingent obligations that are in the scope of these guarantees. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $74 million as of March 31, 2021 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, 2021 and December 31, 2020. 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, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $25 $7 - $19 Current and non-current environmental liabilities $13 $9 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 Burlington by December 31, 2021 and 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: 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

Segments Of Business	3 Months Ended
	Mar. 31, 2021
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73 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): 2021 2020 ATC billings to WPL $32 $28 WPL billings to ATC 3 3 WPL owed ATC net amounts of $9 million as of March 31, 2021 and $9 million as of December 31, 2020.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73 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): 2021 2020 ATC billings to WPL $32 $28 WPL billings to ATC 3 3 WPL owed ATC net amounts of $9 million as of March 31, 2021 and $9 million as of December 31, 2020.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	3 Months Ended
	Mar. 31, 2021
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 latest combined Annual Report on Form 10-K .
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 latest combined Annual Report on Form 10-K .
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 latest combined Annual Report on Form 10-K .
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2021
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $901 $890 $853 $843 $48 $47 Pension and OPEB costs 570 580 286 291 284 289 Asset retirement obligations 120 119 82 81 38 38 Assets retired early 108 113 74 77 34 36 IPL’s DAEC PPA amendment 108 110 108 110 — — WPL’s Western Wisconsin gas distribution expansion investments 55 55 — — 55 55 Derivatives 13 26 6 13 7 13 Other 132 117 85 68 47 49 $2,007 $2,010 $1,494 $1,483 $513 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $685 $732 $327 $331 $358 $401 Cost of removal obligations 371 367 242 238 129 129 Electric transmission cost recovery 67 68 40 39 27 29 WPL’s West Riverside liquidated damages 38 38 — — 38 38 Derivatives 26 28 18 25 8 3 Other 68 73 34 43 34 30 $1,255 $1,306 $661 $676 $594 $630

Receivables (Tables)

Receivables (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding 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): 2021 2020 Maximum outstanding aggregate cash proceeds $100 $96 Average outstanding aggregate cash proceeds 30 24
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2021 December 31, 2020 Customer accounts receivable $124 $114 Unbilled utility revenues 74 92 Receivables sold to third party 198 206 Less: cash proceeds 75 1 Deferred proceeds 123 205 Less: allowance for expected credit losses 16 17 Fair value of deferred proceeds $107 $188
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): 2021 2020 Collections $529 $541 Write-offs, net of recoveries 2 2
IPL [Member]
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding 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): 2021 2020 Maximum outstanding aggregate cash proceeds $100 $96 Average outstanding aggregate cash proceeds 30 24
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2021 December 31, 2020 Customer accounts receivable $124 $114 Unbilled utility revenues 74 92 Receivables sold to third party 198 206 Less: cash proceeds 75 1 Deferred proceeds 123 205 Less: allowance for expected credit losses 16 17 Fair value of deferred proceeds $107 $188
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): 2021 2020 Collections $529 $541 Write-offs, net of recoveries 2 2

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2021
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): 2021 2020 ATC Holdings ($11) ($11) Other (4) (2) ($15) ($13)

Common Equity (Tables)

Common Equity (Tables)	3 Months Ended
	Mar. 31, 2021
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, 2021 249,868,415 Shareowner Direct Plan 152,588 Equity-based compensation plans 113,549 Shares outstanding, March 31, 2021 250,134,552
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436
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 Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436
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 Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 171 171 Common stock dividends ($0.4025 per share) (102) (102) Shareowner Direct Plan issuances 1 7 8 Equity-based compensation plans and other 1 1 Ending balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 170 170 Common stock dividends ($0.38 per share) (93) (93) Equity forward settlements and Shareowner Direct Plan issuances 228 228 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive income, net of tax 1 1 Ending balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 79 79 Common stock dividends (101) (101) Ending balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 83 83 Common stock dividends (60) (60) Capital contributions from parent 100 100 Ending balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 84 84 Common stock dividends (42) (42) Capital contributions from parent 125 125 Ending balance, March 31, 2021 $66 $1,584 $995 $2,645 Three Months Ended March 31, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 90 90 Common stock dividends (43) (43) Capital contributions from parent 25 25 Ending balance, March 31, 2020 $66 $1,459 $911 $2,436

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): March 31, 2021 Alliant Energy IPL WPL Amount outstanding $336 $— $148 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $664 $250 $152 Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $— $1 $275 $212 Average amount outstanding (based on daily outstanding balances) $424 $382 $— $— $189 $167 Weighted average interest rates 0.2% 1.8% —% 1.8% 0.2% 1.8%

Revenues (Tables)

Revenues (Tables)	3 Months Ended
	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $262 $266 $139 $147 $123 $119 Retail - commercial 172 183 110 120 62 63 Retail - industrial 202 210 112 121 90 89 Wholesale 40 40 11 14 29 26 Bulk power and other 25 31 14 23 11 8 Total Electric Utility 701 730 386 425 315 305 Gas Utility: Retail - residential 99 91 52 49 47 42 Retail - commercial 53 45 27 24 26 21 Retail - industrial 5 4 3 2 2 2 Transportation/other 13 12 9 8 4 4 Total Gas Utility 170 152 91 83 79 69 Other Utility: Steam 9 10 9 10 — — Other utility 4 2 3 1 1 1 Total Other Utility 13 12 12 11 1 1 Non-Utility and Other: Transportation and other 17 22 — — — — Total Non-Utility and Other 17 22 — — — — Total revenues $901 $916 $489 $519 $395 $375

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2021
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%)
Summary Of Tax Credit Carryforwards	At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%)
Summary Of Tax Credit Carryforwards	At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements. Alliant Energy IPL WPL Three Months Ended March 31 2021 2020 2021 2020 2021 2020 Overall income tax rate (19%) (12%) (17%) (19%) (29%) (10%)
Summary Of Tax Credit Carryforwards	At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $331 $306 $3 State net operating losses 2021-2041 627 16 2 Federal tax credits 2022-2041 481 280 180

Benefit Plans (Tables)

Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2021
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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61
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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61
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 2021 2020 2021 2020 Service cost $3 $3 $1 $1 Interest cost 8 11 1 2 Expected return on plan assets (17) (18) (1) (2) Amortization of actuarial loss 10 9 1 1 Settlement losses (a) — 4 — — $4 $9 $2 $2 Defined Benefit Pension Plans OPEB Plans IPL 2021 2020 2021 2020 Service cost $2 $1 $— $— Interest cost 4 5 1 1 Expected return on plan assets (8) (8) (1) (1) Amortization of actuarial loss 4 4 — — $2 $2 $— $— Defined Benefit Pension Plans OPEB Plans WPL 2021 2020 2021 2020 Service cost $1 $1 $— $— Interest cost 4 5 — 1 Expected return on plan assets (8) (8) — — Amortization of actuarial loss 5 4 1 — $2 $2 $1 $1 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 2021 2020 2021 2020 2021 2020 Compensation expense $3 $3 $1 $1 $1 $1 Income tax benefits 1 1 — — — —
Schedule Of Equity-based Compensation Plans Activity	For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61

Derivative Instruments (Tables)

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2021, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,531 2021 198,347 2021-2028 5,601 2021-2023 4,914 2021-2022 IPL 1,203 2021 97,747 2021-2028 2,100 2021-2023 — — WPL 2,328 2021 100,600 2021-2027 3,501 2021-2023 4,914 2021-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $18 $24 $12 $20 $6 $4 Non-current derivative assets 10 10 7 9 3 1 Current derivative liabilities 2 9 — 3 2 6 Non-current derivative liabilities 11 16 6 9 5 7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (6) (3) — — Settlements (a) (7) (4) (81) — Ending balance, March 31 $16 $14 $107 $188 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 ($6) ($3) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (5) (2) — — Settlements (a) (6) (3) (81) — Ending balance, March 31 $15 $13 $107 $188 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 ($6) ($2) $— $— (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	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (6) (3) — — Settlements (a) (7) (4) (81) — Ending balance, March 31 $16 $14 $107 $188 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 ($6) ($3) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net losses included in changes in net assets (realized/unrealized) (5) (2) — — Settlements (a) (6) (3) (81) — Ending balance, March 31 $15 $13 $107 $188 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 ($6) ($2) $— $— (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	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2
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, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 28 — 12 16 28 34 — 5 29 34 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 13 — 13 — 13 25 — 25 — 25 Long-term debt (incl. current maturities) 6,779 — 7,613 1 7,614 6,777 — 8,107 2 8,109 IPL March 31, 2021 December 31, 2020 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 $8 $8 $— $— $8 $44 $44 $— $— $44 Derivatives 19 — 4 15 19 29 — 3 26 29 Deferred proceeds 107 — — 107 107 188 — — 188 188 Liabilities: Derivatives 6 — 6 — 6 12 — 12 — 12 Long-term debt 3,346 — 3,745 — 3,745 3,345 — 4,021 — 4,021 WPL March 31, 2021 December 31, 2020 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $9 $— $8 $1 $9 $5 $— $2 $3 $5 Liabilities: Derivatives 7 — 7 — 7 13 — 13 — 13 Long-term debt 2,131 — 2,495 — 2,495 2,130 — 2,690 — 2,690
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2021 $11 $5 $11 $4 $— $1 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies (

Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $25 $7 - $19 Current and non-current environmental liabilities $13 $9
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2021, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $25 $7 - $19 Current and non-current environmental liabilities $13 $9
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At March 31, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $958 $466 $492 Coal 94 55 39 Other (a) 122 60 30 $1,174 $581 $561 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2021.

Segments Of Business (Tables)

Segments Of Business (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended March 31, 2021 Revenues $701 $170 $13 $884 $17 $901 Operating income 147 44 2 193 5 198 Net income attributable to Alliant Energy common shareowners 163 8 171 Three Months Ended March 31, 2020 Revenues $730 $152 $12 $894 $22 $916 Operating income (loss) 146 41 4 191 (3) 188 Net income (loss) attributable to Alliant Energy common shareowners 173 (3) 170 IPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $386 $91 $12 $489 Operating income 72 30 1 103 Net income available for common stock 79 Three Months Ended March 31, 2020 Revenues $425 $83 $11 $519 Operating income 67 27 3 97 Net income available for common stock 83 WPL Electric Gas Other Total (in millions) Three Months Ended March 31, 2021 Revenues $315 $79 $1 $395 Operating income 75 14 1 90 Net income 84 Three Months Ended March 31, 2020 Revenues $305 $69 $1 $375 Operating income 79 14 1 94 Net income 90

Related Parties (Tables)

Related Parties (Tables)	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2021 2020 ATC billings to WPL $32 $28 WPL billings to ATC 3 3
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2021 2020 2021 2020 Corporate Services billings $40 $37 $35 $32 Sales credited 1 15 1 2 Purchases billed 143 81 26 20
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2021 December 31, 2020 March 31, 2021 December 31, 2020 Net payables to Corporate Services $73 $110 $60 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): 2021 2020 ATC billings to WPL $32 $28 WPL billings to ATC 3 3

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Matters [Line Items]
Regulatory assets	$ 2,007	$ 2,010
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	1,494	$ 1,483
Deferred Fuel Costs | IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	$ 20

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 2,007	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	901	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	570	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	120	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	55	55
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	13	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	132	117
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,494	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	853	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	286	291
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	82	81
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	74	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	110
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	6	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	513	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	48	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	284	289
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	38	38
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	34	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	55	55
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	7	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 47	$ 49

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,255	$ 1,306
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	685	732
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	371	367
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	67	68
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	38	38
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26	28
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	68	73
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	661	676
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	327	331
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	242	238
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	39
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	18	25
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	34	43
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	594	630
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	358	401
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	129	129
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27	29
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	38	38
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8	3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 34	$ 30

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - IPL [Member] - USD ($) $ in Millions	Dec. 31, 2021	Mar. 31, 2021
Forecast [Member] | Subsequent Event
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	$ 110
Receivables Sold [Member]
Receivables [Line Items]
Available capacity		$ 15
Receivables Sold [Member] | Financial Asset, Past Due
Receivables [Line Items]
Outstanding receivables past due		$ 22

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 100	$ 96
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 30	$ 24

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Receivables [Line Items]
Fair value of deferred proceeds	$ 107	$ 188
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	107	188
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	124	114
Unbilled utility revenues	74	92
Receivables sold to third party	198	206
Less: cash proceeds	75	1
Deferred proceeds	123	205
Less: allowance for expected credit losses	16	17
Fair value of deferred proceeds	$ 107	$ 188

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Receivables [Line Items]
Collections	$ 529	$ 541
Write-offs, net of recoveries	$ 2	$ 2

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (15)	$ (13)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(11)	(11)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (4)	$ (2)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	3 Months Ended
	Mar. 31, 2021shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2021 (in shares)	249,868,415
Shareowner Direct Plan (in shares)	152,588
Equity-based compensation plans (in shares)	113,549
Shares outstanding, March 31, 2021 (in shares)	250,134,552

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 5,688
Beginning balance	5,888	$ 5,405
Net income attributable to common shareowners	171	170
Net income	174	173
Common stock dividends	(102)	(93)
Equity forward settlements and Shareowner Direct Plan issuances	8	228
Equity-based compensation plans and other	1
Adoption of new accounting standard, net of tax	(3,063)		$ (2,994)
Other comprehensive income, net of tax		1
Ending balance	5,766
Ending balance	$ 5,966	$ 5,702
Common stock dividends (in dollars per share)	$ 0.4025	$ 0.38
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 2	$ 2
Equity forward settlements and Shareowner Direct Plan issuances	1
Ending balance	3	2
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,704	2,446
Equity forward settlements and Shareowner Direct Plan issuances	7	228
Equity-based compensation plans and other	1
Ending balance	2,712	2,674
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,994	2,766
Net income attributable to common shareowners	171	170
Common stock dividends	(102)	(93)
Ending balance	3,063	2,834
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(1)	1
Other comprehensive income, net of tax		1
Ending balance	(1)	2
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(11)	(10)
Equity-based compensation plans and other
Ending balance	(11)	(10)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200
Ending balance	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,764
Beginning balance	3,964	3,472
Net income attributable to common shareowners	79	83
Net income	82	86
Common stock dividends	(101)	(60)
Adoption of new accounting standard, net of tax	(957)		(979)
Capital contributions from parent	0	100
Ending balance	3,742
Ending balance	3,942	3,595
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33
Ending balance	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,752	2,348
Capital contributions from parent		100
Ending balance	2,752	2,448
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	979	891
Net income attributable to common shareowners	79	83
Common stock dividends	(101)	(60)
Ending balance	957	914
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200
Ending balance	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,478
Beginning balance	2,478	2,364
Net income	84	90
Common stock dividends	(42)	(43)
Adoption of new accounting standard, net of tax	(995)		$ (953)
Capital contributions from parent	125	25
Ending balance	2,645
Ending balance	2,645	2,436
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	1,459	1,434
Capital contributions from parent	125	25
Ending balance	1,584	1,459
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	953	864
Net income	84	90
Common stock dividends	(42)	(43)
Ending balance	$ 995	$ 911
Credit Losses ASU [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax				$ (9)
Credit Losses ASU [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax				$ (9)

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Mar. 31, 2021USD ($)
Debt [Line Items]
Amount outstanding	$ 336
Weighted average interest rates	0.20%
Available credit facility capacity	$ 664
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 148
Weighted average interest rates	0.10%
Available credit facility capacity	$ 152

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 578	$ 463
Average amount outstanding (based on daily outstanding balances)	$ 424	$ 382
Weighted average interest rates	0.20%	1.80%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 1
Average amount outstanding (based on daily outstanding balances)	$ 0	$ 0
Weighted average interest rates	0.00%	1.80%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 275	$ 212
Average amount outstanding (based on daily outstanding balances)	$ 189	$ 167
Weighted average interest rates	0.20%	1.80%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 901	$ 916
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	701	730
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	262	266
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	172	183
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	210
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	40	40
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25	31
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	170	152
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	99	91
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	53	45
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	4
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	12
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	12
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	10
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17	22
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17	22
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	489	519
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	386	425
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	139	147
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	110	120
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	112	121
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	14
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	23
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	91	83
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	52	49
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	24
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	11
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	10
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	1
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	395	375
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	315	305
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	123	119
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	63
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90	89
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29	26
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	8
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	79	69
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	42
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	21
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	4
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1	$ 1

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Effective Tax Rate [Line Items]
Overall income tax rate	(19.00%)	(12.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(17.00%)	(19.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(29.00%)	(10.00%)

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2021USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 331
Tax credits, carryforward amount	481
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	306
Tax credits, carryforward amount	280
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Tax credits, carryforward amount	180
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	627
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	16
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 13
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	$ 7
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 5
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	425,849

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3
Interest cost	8	11
Expected return on plan assets	(17)	(18)
Amortization of actuarial loss	10	9
Settlement losses	0	4
Total	4	9
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	1	2
Expected return on plan assets	(1)	(2)
Amortization of actuarial loss	1	1
Settlement losses	0	0
Total	2	2
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1
Interest cost	4	5
Expected return on plan assets	(8)	(8)
Amortization of actuarial loss	4	4
Total	2	2
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	(1)	(1)
Amortization of actuarial loss	0	0
Total	0	0
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	4	5
Expected return on plan assets	(8)	(8)
Amortization of actuarial loss	5	4
Total	2	2
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	1
Expected return on plan assets	0	0
Amortization of actuarial loss	1	0
Total	$ 1	$ 1

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Compensation expense	$ 3	$ 3
Income tax benefits	1	1
IPL [Member]
Compensation expense	1	1
Income tax benefits	0	0
WPL [Member]
Compensation expense	1	1
Income tax benefits	$ 0	$ 0

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	72,774
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 46.19
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	72,774
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.61
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	79,862
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.61

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands, T in Thousands, MWh in Thousands, Dekatherms in Thousands	3 Months Ended
	Mar. 31, 2021DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	3,531
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	1,203
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	2,328
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	198,347
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	97,747
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	100,600
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	5,601
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	2,100
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	3,501
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	4,914
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	4,914

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 18	$ 24
Non-current derivative assets	10	10
Current derivative liabilities	2	9
Non-current derivative liabilities	11	16
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	12	20
Non-current derivative assets	7	9
Current derivative liabilities	0	3
Non-current derivative liabilities	6	9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	6	4
Non-current derivative assets	3	1
Current derivative liabilities	2	6
Non-current derivative liabilities	$ 5	$ 7

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets:
Money market fund investments	$ 8	$ 44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	7,614	8,109
IPL [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	3,745	4,021
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,495	2,690
Commodity Contracts [Member]
Assets:
Derivatives	28	34
Liabilities:
Derivatives	13	25
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	19	29
Liabilities:
Derivatives	6	12
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	5
Liabilities:
Derivatives	7	13
Level 1 [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	7,613	8,107
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,745	4,021
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,495	2,690
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	12	5
Liabilities:
Derivatives	13	25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	4	3
Liabilities:
Derivatives	6	12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	8	2
Liabilities:
Derivatives	7	13
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	1	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	16	29
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	15	26
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	1	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	6,779	6,777
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	3,346	3,345
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,131	2,130
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	28	34
Liabilities:
Derivatives	13	25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	19	29
Liabilities:
Derivatives	6	12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	5
Liabilities:
Derivatives	$ 7	$ 13

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 29	$ 21
Total net losses included in changes in net assets (realized/unrealized)	(6)	(3)
Settlements	(7)	(4)
Ending balance	16	14
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	(6)	(3)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	26	18
Total net losses included in changes in net assets (realized/unrealized)	(5)	(2)
Settlements	(6)	(3)
Ending balance	15	13
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	(6)	(2)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	188	188
Total net losses included in changes in net assets (realized/unrealized)	0	0
Settlements	(81)	0
Ending balance	107	188
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	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	188	188
Total net losses included in changes in net assets (realized/unrealized)	0	0
Settlements	(81)	0
Ending balance	107	188
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	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 16	$ 29	$ 14	$ 21
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	11	18
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	5	11
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	15	26	$ 13	$ 18
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	11	17
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	4	9
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	1
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 1	$ 2

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,174
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	581
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	561
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	10
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	10
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	74
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	$ 17
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent	6.00%
Obligations, maximum	$ 68
Credit loss liability	$ 5

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,174
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	581
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	561
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	958
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	466
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	492
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	94
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	55
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	39
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	122
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	60
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 30

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
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	9
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	9
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	7
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	25
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 19

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 901	$ 916
Operating income (loss)	198	188
Net income (loss) attributable to common shareowners	171	170
Net income	174	173
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	489	519
Operating income (loss)	103	97
Net income (loss) attributable to common shareowners	79	83
Net income	82	86
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	395	375
Operating income (loss)	90	94
Net income	84	90
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	701	730
Operating income (loss)	147	146
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	386	425
Operating income (loss)	72	67
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	315	305
Operating income (loss)	75	79
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	170	152
Operating income (loss)	44	41
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	91	83
Operating income (loss)	30	27
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	79	69
Operating income (loss)	14	14
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	13	12
Operating income (loss)	2	4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	12	11
Operating income (loss)	1	3
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1	1
Operating income (loss)	1	1
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	884	894
Operating income (loss)	193	191
Net income (loss) attributable to common shareowners	163	173
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	17	22
Operating income (loss)	5	(3)
Net income (loss) attributable to common shareowners	$ 8	$ (3)

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ATC LLC [Member] | WPL Owed ATC LLC [Member] | Equity Method Investee [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 9	$ 9

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 40	$ 37
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	35	32
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	1	15
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	1	2
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	143	81
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 26	$ 20

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 73	$ 110
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 60	$ 73

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 32	$ 28
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 3	$ 3