Alliant Energy (LNT) 10-Q 5 Nov 21 2021 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2021shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 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	250,360,787
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Electric utility	$ 939	$ 852	$ 2,357	$ 2,257
Gas utility	50	42	289	253
Other utility	13	10	36	32
Non-utility	22	16	60	57
Total revenues	1,024	920	2,742	2,599
Operating expenses:
Electric production fuel and purchased power	207	179	478	527
Electric transmission service	148	132	403	326
Cost of gas sold	18	11	149	117
Other operation and maintenance	171	143	477	465
Depreciation and amortization	165	156	494	454
Taxes other than income taxes	26	27	78	82
Total operating expenses	735	648	2,079	1,971
Operating income	289	272	663	628
Other (income) and deductions:
Interest expense	68	68	206	207
Equity income from unconsolidated investments, net	(13)	(15)	(47)	(46)
Allowance for funds used during construction	(7)	(13)	(16)	(51)
Other	3	3	7	7
Total other (income) and deductions	51	43	150	117
Income before income taxes	238	229	513	511
Income tax benefit	(21)	(20)	(66)	(47)
Net income	259	249	579	558
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	$ 256	$ 246	$ 571	$ 550
Weighted average number of common shares outstanding:
Basic (in shares)	250.3	249.7	250.2	247.9
Diluted (in shares)	250.8	250	250.6	248.1
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 1.02	$ 0.99	$ 2.28	$ 2.22
Diluted (in dollars per share)	$ 1.02	$ 0.98	$ 2.28	$ 2.22
IPL [Member]
Revenues:
Electric utility	$ 555	$ 519	$ 1,343	$ 1,332
Gas utility	31	24	165	141
Other utility	13	10	35	31
Total revenues	599	553	1,543	1,504
Operating expenses:
Electric production fuel and purchased power	101	102	215	304
Electric transmission service	103	93	274	212
Cost of gas sold	12	6	84	63
Other operation and maintenance	95	85	253	269
Depreciation and amortization	94	89	281	264
Taxes other than income taxes	14	16	42	45
Total operating expenses	419	391	1,149	1,157
Operating income	180	162	394	347
Other (income) and deductions:
Interest expense	34	35	103	104
Allowance for funds used during construction	(2)	(6)	(7)	(21)
Other	0	1	2	3
Total other (income) and deductions	32	30	98	86
Income before income taxes	148	132	296	261
Income tax benefit	(12)	(19)	(34)	(37)
Net income	160	151	330	298
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	157	148	322	290
WPL [Member]
Revenues:
Electric utility	384	333	1,014	925
Gas utility	19	18	124	112
Other utility	0	0	1	1
Total revenues	403	351	1,139	1,038
Operating expenses:
Electric production fuel and purchased power	105	78	263	223
Electric transmission service	44	39	128	114
Cost of gas sold	6	4	65	53
Other operation and maintenance	66	65	194	172
Depreciation and amortization	70	65	209	186
Taxes other than income taxes	12	11	35	35
Total operating expenses	303	262	894	783
Operating income	100	89	245	255
Other (income) and deductions:
Interest expense	25	26	77	78
Allowance for funds used during construction	(5)	(6)	(9)	(29)
Other	2	1	3	3
Total other (income) and deductions	22	21	71	52
Income before income taxes	78	68	174	203
Income tax benefit	(15)	(5)	(41)	(17)
Net income	$ 93	$ 73	$ 215	$ 220

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 20	$ 54
Accounts receivable, less allowance for expected credit losses	392	412
Production fuel, at weighted average cost	42	66
Gas stored underground, at weighted average cost	58	46
Materials and supplies, at weighted average cost	118	105
Regulatory assets	111	81
Other	274	123
Total current assets	1,015	887
Property, plant and equipment, net	14,738	14,336
Investments:
ATC Holdings	338	331
Other	176	154
Total investments	514	485
Other assets:
Regulatory assets	1,907	1,929
Deferred charges and other	155	73
Total other assets	2,062	2,002
Total assets	18,329	17,710
Current liabilities:
Current maturities of long-term debt	383	8
Commercial paper	316	389
Accounts payable	361	377
Regulatory liabilities	231	249
Other	266	274
Total current liabilities	1,557	1,297
Long-term debt, net (excluding current portion)	6,692	6,769
Other liabilities:
Deferred tax liabilities	1,906	1,814
Regulatory liabilities	1,130	1,057
Pension and other benefit obligations	452	511
Other	407	374
Total other liabilities	3,895	3,756
Commitments and contingencies (Note 14)
Common equity:
Common stock	3	2
Additional paid-in capital	2,733	2,704
Retained earnings	3,261	2,994
Accumulated other comprehensive loss	(1)	(1)
Shares in deferred compensation trust - 377,875 and 380,542 shares at a weighted average cost of $30.14 and $28.73 per share	(11)	(11)
Total common equity	5,985	5,688
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	6,185	5,888
Total liabilities and equity	18,329	17,710
IPL [Member]
Current assets:
Cash and cash equivalents	13	50
Accounts receivable, less allowance for expected credit losses	205	210
Production fuel, at weighted average cost	32	48
Gas stored underground, at weighted average cost	33	20
Materials and supplies, at weighted average cost	71	63
Regulatory assets	86	52
Other	108	53
Total current assets	548	496
Property, plant and equipment, net	7,931	7,889
Other assets:
Regulatory assets	1,421	1,431
Deferred charges and other	78	33
Total other assets	1,499	1,464
Total assets	9,978	9,849
Current liabilities:
Accounts payable	140	162
Regulatory liabilities	104	103
Other	171	182
Total current liabilities	415	447
Long-term debt, net (excluding current portion)	3,347	3,345
Other liabilities:
Deferred tax liabilities	1,079	1,035
Regulatory liabilities	616	573
Pension and other benefit obligations	161	186
Other	325	299
Total other liabilities	2,181	2,093
Commitments and contingencies (Note 14)
Common equity:
Common stock	33	33
Additional paid-in capital	2,802	2,752
Retained earnings	1,000	979
Total common equity	3,835	3,764
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	4,035	3,964
Total liabilities and equity	9,978	9,849
WPL [Member]
Current assets:
Cash and cash equivalents	4	3
Accounts receivable, less allowance for expected credit losses	175	192
Production fuel, at weighted average cost	10	18
Gas stored underground, at weighted average cost	25	26
Materials and supplies, at weighted average cost	45	40
Regulatory assets	25	29
Prepaid gross receipts tax	29	42
Other	99	12
Total current assets	412	362
Property, plant and equipment, net	6,367	6,022
Other assets:
Regulatory assets	486	498
Deferred charges and other	76	30
Total other assets	562	528
Total assets	7,341	6,912
Current liabilities:
Commercial paper	3	257
Accounts payable	160	154
Regulatory liabilities	127	146
Other	116	117
Total current liabilities	406	674
Long-term debt, net (excluding current portion)	2,429	2,130
Other liabilities:
Deferred tax liabilities	747	702
Regulatory liabilities	514	484
Finance lease obligations - Sheboygan Falls Energy Facility	34	42
Pension and other benefit obligations	193	222
Other	206	180
Total other liabilities	1,694	1,630
Commitments and contingencies (Note 14)
Common equity:
Common stock	66	66
Additional paid-in capital	1,704	1,459
Retained earnings	1,042	953
Total common equity	2,812	2,478
Total equity	2,812	2,478
Total liabilities and equity	$ 7,341	$ 6,912

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 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)	250,360,787	249,868,415
Shares in deferred compensation trust (in shares)	377,875	380,542
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 30.14	$ 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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income	$ 579	$ 558
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	494	454
Deferred tax benefit and tax credits	(69)	(48)
Other	7	(17)
Other changes in assets and liabilities:
Accounts receivable	(397)	(316)
Derivative assets	(202)	(22)
Regulatory liabilities	25	(72)
Deferred income taxes	160	143
Pension and other benefit obligations	(59)	(61)
DAEC PPA amendment buyout payment	0	(110)
Other	(61)	(73)
Net cash flows from operating activities	477	436
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(772)	(935)
Other construction and acquisition expenditures	(60)	(39)
Cash receipts on sold receivables	423	318
Other	(43)	(23)
Net cash flows from (used for) investing activities	(452)	(679)
Cash flows from (used for) financing activities:
Common stock dividends	(304)	(281)
Proceeds from issuance of common stock, net	22	241
Proceeds from issuance of long-term debt	300	1,050
Payments to retire long-term debt	(4)	(654)
Net change in commercial paper	(73)	85
Other	2	(22)
Net cash flows from (used for) financing activities	(57)	419
Net increase (decrease) in cash, cash equivalents and restricted cash	(32)	176
Cash, cash equivalents and restricted cash at beginning of period	56	18
Cash, cash equivalents and restricted cash at end of period	24	194
Supplemental cash flows information:
Interest	(197)	(197)
Income taxes, net	(1)	6
Significant non-cash investing and financing activities:
Accrued capital expenditures	91	202
Beneficial interest obtained in exchange for securitized accounts receivable	164	201
IPL [Member]
Cash flows from operating activities:
Net income	330	298
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	281	264
Deferred tax benefit and tax credits	(13)	(42)
Other	(1)	(9)
Other changes in assets and liabilities:
Accounts receivable	(412)	(337)
Derivative assets	(86)	(12)
Regulatory assets	(33)	(32)
Regulatory liabilities	30	(11)
Deferred income taxes	56	62
Pension and other benefit obligations	(25)	(19)
DAEC PPA amendment buyout payment	0	(110)
Other	(32)	(33)
Net cash flows from operating activities	95	19
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(285)	(465)
Cash receipts on sold receivables	423	318
Other	(16)	(55)
Net cash flows from (used for) investing activities	122	(202)
Cash flows from (used for) financing activities:
Common stock dividends	(301)	(177)
Capital contributions from parent	50	345
Proceeds from issuance of long-term debt	0	400
Payments to retire long-term debt	0	(200)
Other	(3)	(9)
Net cash flows from (used for) financing activities	(254)	359
Net increase (decrease) in cash, cash equivalents and restricted cash	(37)	176
Cash, cash equivalents and restricted cash at beginning of period	50	9
Cash, cash equivalents and restricted cash at end of period	13	185
Supplemental cash flows information:
Interest	(106)	(109)
Income taxes, net	28	(12)
Significant non-cash investing and financing activities:
Accrued capital expenditures	30	150
Beneficial interest obtained in exchange for securitized accounts receivable	164	201
WPL [Member]
Cash flows from operating activities:
Net income	215	220
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	209	186
Deferred tax benefit and tax credits	(63)	(9)
Other	12	(8)
Other changes in assets and liabilities:
Derivative assets	(116)	(10)
Regulatory liabilities	(5)	(61)
Deferred income taxes	108	79
Other	(11)	5
Net cash flows from operating activities	349	402
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(487)	(470)
Other	(23)	5
Net cash flows from (used for) investing activities	(510)	(465)
Cash flows from (used for) financing activities:
Common stock dividends	(126)	(127)
Capital contributions from parent	245	25
Proceeds from issuance of long-term debt	300	350
Payments to retire long-term debt	0	(150)
Net change in commercial paper	(254)	(29)
Other	(3)	(8)
Net cash flows from (used for) financing activities	162	61
Net increase (decrease) in cash, cash equivalents and restricted cash	1	(2)
Cash, cash equivalents and restricted cash at beginning of period	3	4
Cash, cash equivalents and restricted cash at end of period	4	2
Supplemental cash flows information:
Interest	(72)	(71)
Income taxes, net	(24)	5
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 59	$ 50

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 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 SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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 nine months ended September 30, 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. NOTE 1(b) Asset Impairments - Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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 nine months ended September 30, 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. NOTE 1(b) Asset Impairments - Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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 nine months ended September 30, 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. NOTE 1(b) Asset Impairments - Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527 Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $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 nine months ended September 30, 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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527 Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $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 nine months ended September 30, 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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527 Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $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 nine months ended September 30, 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	9 Months Ended
	Sep. 30, 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. 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. As of September 30, 2021, IPL had $60 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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $1 $110 $96 Average outstanding aggregate cash proceeds 65 1 52 12 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2021 December 31, 2020 Customer accounts receivable $145 $114 Unbilled utility revenues 83 92 Receivables sold to third party 228 206 Less: cash proceeds 50 1 Deferred proceeds 178 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $164 $188 As of September 30, 2021, outstanding receivables past due under the Receivables Agreement were $19 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Collections $607 $561 $1,589 $1,555 Write-offs, net of recoveries 4 1 7 4
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. 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. As of September 30, 2021, IPL had $60 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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $1 $110 $96 Average outstanding aggregate cash proceeds 65 1 52 12 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2021 December 31, 2020 Customer accounts receivable $145 $114 Unbilled utility revenues 83 92 Receivables sold to third party 228 206 Less: cash proceeds 50 1 Deferred proceeds 178 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $164 $188 As of September 30, 2021, outstanding receivables past due under the Receivables Agreement were $19 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Collections $607 $561 $1,589 $1,555 Write-offs, net of recoveries 4 1 7 4

Investments

Investments	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC Holdings ($12) ($11) ($34) ($36) Other (1) (4) (13) (10) ($13) ($15) ($47) ($46)

Common Equity

Common Equity	9 Months Ended
	Sep. 30, 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 378,823 Equity-based compensation plans 113,549 Shares outstanding, September 30, 2021 250,360,787 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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482
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 378,823 Equity-based compensation plans 113,549 Shares outstanding, September 30, 2021 250,360,787 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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482
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 378,823 Equity-based compensation plans 113,549 Shares outstanding, September 30, 2021 250,360,787 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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482

Preferred Stock

Preferred Stock	9 Months Ended
	Sep. 30, 2021
Preferred Stock	PREFERRED STOCKIn November 2021, IPL announced it will redeem all 8,000,000 outstanding shares of its 5.1% cumulative preferred stock in December 2021 at par value for approximately $200 million plus accrued and unpaid dividends up to the redemption date.
IPL [Member]
Preferred Stock	PREFERRED STOCKIn November 2021, IPL announced it will redeem all 8,000,000 outstanding shares of its 5.1% cumulative preferred stock in December 2021 at par value for approximately $200 million plus accrued and unpaid dividends up to the redemption date.

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In the third quarter of 2021, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $100 million for IPL and $400 million for WPL, within the $1 billion total commitment. 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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2% NOTE 7(b) Long-term Debt - In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be disbursed for the construction and development of WPL’s wind and solar EGUs.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In the third quarter of 2021, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $100 million for IPL and $400 million for WPL, within the $1 billion total commitment. 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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2% NOTE 7(b) Long-term Debt - In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be disbursed for the construction and development of WPL’s wind and solar EGUs.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In the third quarter of 2021, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $100 million for IPL and $400 million for WPL, within the $1 billion total commitment. 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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2% NOTE 7(b) Long-term Debt - In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be disbursed for the construction and development of WPL’s wind and solar EGUs.

Revenues

Revenues	9 Months Ended
	Sep. 30, 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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038
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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038
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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%) Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186
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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%) Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186
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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%) Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2021
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1 As of September 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65 As of September 30, 2021, 491,406 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1 As of September 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65 As of September 30, 2021, 491,406 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1 As of September 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65 As of September 30, 2021, 491,406 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2021
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 37 32 Liabilities settled (10) (8) Liabilities incurred 1 — Accretion expense 6 4 Balance, September 30 $285 $205
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 37 32 Liabilities settled (10) (8) Liabilities incurred 1 — Accretion expense 6 4 Balance, September 30 $285 $205

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2021
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7 During the nine months ended September 30, 2021, Alliant Energy’s, IPL’s and WPL’s derivative assets increased and derivative liabilities decreased primarily as a result of higher natural gas prices. Based on IPL’s and WPL’s natural gas cost recovery mechanisms, this resulted in corresponding decreases in derivative regulatory assets and increases in derivative regulatory liabilities on the balance sheets. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided 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 September 30, 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 September 30, 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 September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7 During the nine months ended September 30, 2021, Alliant Energy’s, IPL’s and WPL’s derivative assets increased and derivative liabilities decreased primarily as a result of higher natural gas prices. Based on IPL’s and WPL’s natural gas cost recovery mechanisms, this resulted in corresponding decreases in derivative regulatory assets and increases in derivative regulatory liabilities on the balance sheets. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided 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 September 30, 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 September 30, 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 September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7 During the nine months ended September 30, 2021, Alliant Energy’s, IPL’s and WPL’s derivative assets increased and derivative liabilities decreased primarily as a result of higher natural gas prices. Based on IPL’s and WPL’s natural gas cost recovery mechanisms, this resulted in corresponding decreases in derivative regulatory assets and increases in derivative regulatory liabilities on the balance sheets. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided 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 September 30, 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 September 30, 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	9 Months Ended
	Sep. 30, 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30 2021 2020 2021 2020 Beginning balance, July 1 $39 $36 $154 $194 Total net gains included in changes in net assets (realized/unrealized) 5 — — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (7) (5) 10 7 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5 ($1) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 6 8 — — Transfers out of Level 3 (8) — — — Purchases 21 14 — — Sales — (1) — — Settlements (a) (19) (12) (24) 13 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $6 $8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2021 2020 2021 2020 Beginning balance, July 1 $30 $32 $154 $194 Total net gains (losses) included in changes in net assets (realized/unrealized) 2 (1) — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (5) (4) 10 7 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $2 ($1) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains included in changes in net assets (realized/unrealized) — 7 — — Transfers out of Level 3 (8) — — — Purchases 16 11 — — Sales — (1) — — Settlements (a) (15) (9) (24) 13 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $7 $— $— (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 September 30, 2021 $7 $22 $5 $14 $2 $8 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30 2021 2020 2021 2020 Beginning balance, July 1 $39 $36 $154 $194 Total net gains included in changes in net assets (realized/unrealized) 5 — — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (7) (5) 10 7 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5 ($1) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 6 8 — — Transfers out of Level 3 (8) — — — Purchases 21 14 — — Sales — (1) — — Settlements (a) (19) (12) (24) 13 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $6 $8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2021 2020 2021 2020 Beginning balance, July 1 $30 $32 $154 $194 Total net gains (losses) included in changes in net assets (realized/unrealized) 2 (1) — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (5) (4) 10 7 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $2 ($1) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains included in changes in net assets (realized/unrealized) — 7 — — Transfers out of Level 3 (8) — — — Purchases 16 11 — — Sales — (1) — — Settlements (a) (15) (9) (24) 13 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $7 $— $— (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 September 30, 2021 $7 $22 $5 $14 $2 $8 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30 2021 2020 2021 2020 Beginning balance, July 1 $39 $36 $154 $194 Total net gains included in changes in net assets (realized/unrealized) 5 — — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (7) (5) 10 7 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5 ($1) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 6 8 — — Transfers out of Level 3 (8) — — — Purchases 21 14 — — Sales — (1) — — Settlements (a) (19) (12) (24) 13 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $6 $8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2021 2020 2021 2020 Beginning balance, July 1 $30 $32 $154 $194 Total net gains (losses) included in changes in net assets (realized/unrealized) 2 (1) — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (5) (4) 10 7 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $2 ($1) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains included in changes in net assets (realized/unrealized) — 7 — — Transfers out of Level 3 (8) — — — Purchases 16 11 — — Sales — (1) — — Settlements (a) (15) (9) (24) 13 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $7 $— $— (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 September 30, 2021 $7 $22 $5 $14 $2 $8 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At September 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $95 million and $93 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021. NOTE 14(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 September 30, 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 September 30, 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 $67 million as of September 30, 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 September 30, 2021 and December 31, 2020. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At September 30, 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 September 30, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $24 $6 - $19 Current and non-current environmental liabilities $12 $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 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At September 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $95 million and $93 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021. NOTE 14(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 September 30, 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 September 30, 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 $67 million as of September 30, 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 September 30, 2021 and December 31, 2020. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At September 30, 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 September 30, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $24 $6 - $19 Current and non-current environmental liabilities $12 $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 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At September 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $95 million and $93 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021. NOTE 14(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 September 30, 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 September 30, 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 $67 million as of September 30, 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 September 30, 2021 and December 31, 2020. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At September 30, 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 September 30, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $24 $6 - $19 Current and non-current environmental liabilities $12 $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	9 Months Ended
	Sep. 30, 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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220
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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220
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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC billings to WPL $29 $27 $91 $80 WPL billings to ATC 4 2 13 8 WPL owed ATC net amounts of $8 million as of September 30, 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 and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $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 and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC billings to WPL $29 $27 $91 $80 WPL billings to ATC 4 2 13 8 WPL owed ATC net amounts of $8 million as of September 30, 2021 and $9 million as of December 31, 2020.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2021
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2020 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.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - In the second quarter of 2021, WPL received approval from MISO to retire Columbia Units 1 and 2, which had a net book value of approximately $470 million in aggregate as of September 30, 2021, and currently anticipates retiring Columbia Unit 1 by the end of 2023 and Columbia Unit 2 by the end of 2024. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of September 30, 2021. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, Alliant Energy and WPL concluded that no disallowance was required as of September 30, 2021.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2021
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $630
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $630
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $931 $890 $881 $843 $50 $47 Pension and OPEB costs 549 580 276 291 273 289 Asset retirement obligations 124 119 85 81 39 38 Assets retired early 98 113 69 77 29 36 IPL’s DAEC PPA amendment 96 110 96 110 — — WPL’s Western Wisconsin gas distribution expansion investments 53 55 — — 53 55 Commodity cost recovery 32 4 17 1 15 3 Derivatives 4 26 4 13 — 13 Other 131 113 79 67 52 46 $2,018 $2,010 $1,507 $1,483 $511 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $611 $732 $313 $331 $298 $401 Cost of removal obligations 383 367 252 238 131 129 Derivatives 221 28 104 25 117 3 Electric transmission cost recovery 53 68 29 39 24 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 53 73 22 43 31 30 $1,361 $1,306 $720 $676 $641 $630

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $1 $110 $96 Average outstanding aggregate cash proceeds 65 1 52 12
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2021 December 31, 2020 Customer accounts receivable $145 $114 Unbilled utility revenues 83 92 Receivables sold to third party 228 206 Less: cash proceeds 50 1 Deferred proceeds 178 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $164 $188
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Collections $607 $561 $1,589 $1,555 Write-offs, net of recoveries 4 1 7 4
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 and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $1 $110 $96 Average outstanding aggregate cash proceeds 65 1 52 12
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2021 December 31, 2020 Customer accounts receivable $145 $114 Unbilled utility revenues 83 92 Receivables sold to third party 228 206 Less: cash proceeds 50 1 Deferred proceeds 178 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $164 $188
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 Collections $607 $561 $1,589 $1,555 Write-offs, net of recoveries 4 1 7 4

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC Holdings ($12) ($11) ($34) ($36) Other (1) (4) (13) (10) ($13) ($15) ($47) ($46)

Common Equity (Tables)

Common Equity (Tables)	9 Months Ended
	Sep. 30, 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 378,823 Equity-based compensation plans 113,549 Shares outstanding, September 30, 2021 250,360,787
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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482
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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482
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 September 30, 2021 Beginning balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Net income attributable to Alliant Energy common shareowners 256 256 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 5 5 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 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 Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $2 $2,704 $2,994 ($1) ($11) $200 $5,888 Net income attributable to Alliant Energy common shareowners 571 571 Common stock dividends ($1.2075 per share) (304) (304) Shareowner Direct Plan issuances 1 21 22 Equity-based compensation plans and other 8 8 Ending balance, September 30, 2021 $3 $2,733 $3,261 ($1) ($11) $200 $6,185 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281) (281) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1) 5 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1) ($11) $200 $5,909 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Net income available for common stock 157 157 Common stock dividends (101) (101) Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59) (59) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 322 322 Common stock dividends (301) (301) Capital contributions from parent 50 50 Ending balance, September 30, 2021 $33 $2,802 $1,000 $200 $4,035 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177) (177) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2021 Beginning balance, June 30, 2021 $66 $1,669 $990 $2,725 Net income 93 93 Common stock dividends (41) (41) Capital contributions from parent 35 35 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43) (43) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 215 215 Common stock dividends (126) (126) Capital contributions from parent 245 245 Ending balance, September 30, 2021 $66 $1,704 $1,042 $2,812 Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127) (127) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2%
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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2%
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): September 30, 2021 Alliant Energy IPL WPL Amount outstanding $316 $— $3 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $684 $100 $397 Alliant Energy IPL WPL Three Months Ended September 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $648 $422 $8 $— $320 $139 Average amount outstanding (based on daily outstanding balances) $560 $252 $— $— $221 $83 Weighted average interest rates 0.2% 0.2% 0.2% N/A 0.1% 0.2% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $648 $463 $19 $8 $320 $212 Average amount outstanding (based on daily outstanding balances) $479 $252 $— $— $196 $86 Weighted average interest rates 0.2% 1.1% 0.2% 0.5% 0.1% 1.2%

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 30, 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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038
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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038
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 September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $348 $328 $207 $189 $141 $139 Retail - commercial 232 210 160 142 72 68 Retail - industrial 265 241 158 149 107 92 Wholesale 55 47 18 17 37 30 Bulk power and other 39 26 12 22 27 4 Total Electric Utility 939 852 555 519 384 333 Gas Utility: Retail - residential 24 22 14 12 10 10 Retail - commercial 13 10 8 6 5 4 Retail - industrial 3 2 3 1 — 1 Transportation/other 10 8 6 5 4 3 Total Gas Utility 50 42 31 24 19 18 Other Utility: Steam 9 8 9 8 — — Other utility 4 2 4 2 — — Total Other Utility 13 10 13 10 — — Non-Utility and Other: Travero and other 22 16 — — — — Total Non-Utility and Other 22 16 — — — — Total revenues $1,024 $920 $599 $553 $403 $351 Alliant Energy IPL WPL Nine Months Ended September 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $868 $845 $488 $472 $380 $373 Retail - commercial 579 556 385 371 194 185 Retail - industrial 677 648 386 384 291 264 Wholesale 142 127 44 44 98 83 Bulk power and other 91 81 40 61 51 20 Total Electric Utility 2,357 2,257 1,343 1,332 1,014 925 Gas Utility: Retail - residential 162 146 90 79 72 67 Retail - commercial 85 70 47 38 38 32 Retail - industrial 11 8 8 5 3 3 Transportation/other 31 29 20 19 11 10 Total Gas Utility 289 253 165 141 124 112 Other Utility: Steam 27 27 27 27 — — Other utility 9 5 8 4 1 1 Total Other Utility 36 32 35 31 1 1 Non-Utility and Other: Travero and other 60 57 — — — — Total Non-Utility and Other 60 57 — — — — Total revenues $2,742 $2,599 $1,543 $1,504 $1,139 $1,038

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%)
Summary Of Tax Credit Carryforwards	At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186
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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%)
Summary Of Tax Credit Carryforwards	At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186
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 and nine months ended September 30, 2021 compared to the same periods 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 Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (9%) (9%) (13%) (9%) (8%) (14%) (11%) (14%) (19%) (7%) (24%) (8%)
Summary Of Tax Credit Carryforwards	At September 30, 2021, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $170 $157 $1 State net operating losses 2021-2041 592 24 2 Federal tax credits 2022-2041 547 339 186

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (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 and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (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 and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $3 $8 $8 $1 $1 $3 $3 Interest cost 9 10 26 32 1 2 3 5 Expected return on plan assets (17) (17) (51) (52) (1) (1) (3) (4) Amortization of prior service credit (1) — (1) — — — — — Amortization of actuarial loss 10 9 29 26 1 — 3 2 Settlement losses (a) — — — 4 — — — — $3 $5 $11 $18 $2 $2 $6 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $2 $5 $5 $— $— $1 $1 Interest cost 4 5 12 15 1 1 2 2 Expected return on plan assets (8) (8) (24) (24) (1) (1) (3) (3) Amortization of actuarial loss 5 4 13 11 — — 1 1 $2 $3 $6 $7 $— $— $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $3 $3 $1 $— $1 $1 Interest cost 3 5 11 14 — 1 1 2 Expected return on plan assets (8) (8) (23) (23) — (1) — (1) Amortization of actuarial loss 5 4 14 12 1 1 2 2 $1 $2 $5 $6 $2 $1 $4 $4 (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 and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $4 $5 $9 $10 $2 $3 $5 $6 $2 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 2 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 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 73,112 $46.19 Performance restricted stock units 73,112 48.66 Restricted stock units 80,152 48.65

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2021
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 37 32 Liabilities settled (10) (8) Liabilities incurred 1 — Accretion expense 6 4 Balance, September 30 $285 $205
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 37 32 Liabilities settled (10) (8) Liabilities incurred 1 — Accretion expense 6 4 Balance, September 30 $285 $205

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 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 13,265 2021-2022 189,332 2021-2030 4,280 2021-2023 3,654 2021-2022 IPL 4,014 2021-2022 103,859 2021-2030 1,807 2021-2023 — — WPL 9,251 2021-2022 85,473 2021-2030 2,473 2021-2023 3,654 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $158 $24 $72 $20 $86 $4 Non-current derivative assets 78 10 43 9 35 1 Current derivative liabilities 3 9 3 3 — 6 Non-current derivative liabilities 1 16 1 9 — 7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30 2021 2020 2021 2020 Beginning balance, July 1 $39 $36 $154 $194 Total net gains included in changes in net assets (realized/unrealized) 5 — — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (7) (5) 10 7 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5 ($1) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 6 8 — — Transfers out of Level 3 (8) — — — Purchases 21 14 — — Sales — (1) — — Settlements (a) (19) (12) (24) 13 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $6 $8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2021 2020 2021 2020 Beginning balance, July 1 $30 $32 $154 $194 Total net gains (losses) included in changes in net assets (realized/unrealized) 2 (1) — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (5) (4) 10 7 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $2 ($1) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains included in changes in net assets (realized/unrealized) — 7 — — Transfers out of Level 3 (8) — — — Purchases 16 11 — — Sales — (1) — — Settlements (a) (15) (9) (24) 13 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $7 $— $— (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 September 30, 2021 $7 $22 $5 $14 $2 $8 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30 2021 2020 2021 2020 Beginning balance, July 1 $39 $36 $154 $194 Total net gains included in changes in net assets (realized/unrealized) 5 — — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (7) (5) 10 7 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5 ($1) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 6 8 — — Transfers out of Level 3 (8) — — — Purchases 21 14 — — Sales — (1) — — Settlements (a) (19) (12) (24) 13 Ending balance, September 30 $29 $30 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $6 $8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2021 2020 2021 2020 Beginning balance, July 1 $30 $32 $154 $194 Total net gains (losses) included in changes in net assets (realized/unrealized) 2 (1) — — Transfers out of Level 3 (8) — — — Sales — (1) — — Settlements (a) (5) (4) 10 7 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $2 ($1) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains included in changes in net assets (realized/unrealized) — 7 — — Transfers out of Level 3 (8) — — — Purchases 16 11 — — Sales — (1) — — Settlements (a) (15) (9) (24) 13 Ending balance, September 30 $19 $26 $164 $201 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $7 $— $— (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 September 30, 2021 $7 $22 $5 $14 $2 $8 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 September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 236 — 207 29 236 34 — 5 29 34 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 25 — 25 — 25 Long-term debt (incl. current maturities) 7,075 — 8,083 1 8,084 6,777 — 8,107 2 8,109 IPL September 30, 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 $9 $9 $— $— $9 $44 $44 $— $— $44 Derivatives 115 — 96 19 115 29 — 3 26 29 Deferred proceeds 164 — — 164 164 188 — — 188 188 Liabilities: Derivatives 4 — 4 — 4 12 — 12 — 12 Long-term debt 3,347 — 3,849 — 3,849 3,345 — 4,021 — 4,021 WPL September 30, 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 $121 $— $111 $10 $121 $5 $— $2 $3 $5 Liabilities: Derivatives — — — — — 13 — 13 — 13 Long-term debt 2,429 — 2,869 — 2,869 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 September 30, 2021 $7 $22 $5 $14 $2 $8 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies (

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 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 September 30, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $24 $6 - $19 Current and non-current environmental liabilities $12 $9
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 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 September 30, 2021, such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $9 - $24 $6 - $19 Current and non-current environmental liabilities $12 $9
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $985 $514 $471 Coal 82 54 28 Other (a) 134 71 39 $1,201 $639 $538 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2021.

Segments Of Business (Tables)

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220
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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220
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 September 30, 2021 Revenues $939 $50 $13 $1,002 $22 $1,024 Operating income (loss) 290 (5) (5) 280 9 289 Net income attributable to Alliant Energy common shareowners 250 6 256 Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2021 Revenues $2,357 $289 $36 $2,682 $60 $2,742 Operating income (loss) 601 42 (4) 639 24 663 Net income attributable to Alliant Energy common shareowners 537 34 571 Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $555 $31 $13 $599 Operating income (loss) 186 (3) (3) 180 Net income available for common stock 157 Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Nine Months Ended September 30, 2021 Revenues $1,343 $165 $35 $1,543 Operating income (loss) 365 30 (1) 394 Net income available for common stock 322 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2021 Revenues $384 $19 $— $403 Operating income (loss) 104 (2) (2) 100 Net income 93 Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2) (1) 89 Net income 73 Nine Months Ended September 30, 2021 Revenues $1,014 $124 $1 $1,139 Operating income (loss) 236 12 (3) 245 Net income 215 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220

Related Parties (Tables)

Related Parties (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC billings to WPL $29 $27 $91 $80 WPL billings to ATC 4 2 13 8
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $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 and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $50 $53 $138 $134 $37 $41 $113 $108 Sales credited 4 10 9 35 16 — 23 4 Purchases billed 105 110 347 248 24 39 71 79
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Net payables to Corporate Services $109 $110 $80 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2021 2020 2021 2020 ATC billings to WPL $29 $27 $91 $80 WPL billings to ATC 4 2 13 8

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	Sep. 30, 2021USD ($)
WPL [Member] | Columbia Units 1 and 2 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Electric plant anticipated to be retired early	$ 470

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Matters [Line Items]
Regulatory assets	$ 2,018	$ 2,010
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	1,507	1,483
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	511	$ 527
Deferred Fuel Costs | IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	15
Deferred Fuel Costs | WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	$ 12

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 2,018	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	931	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	549	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	124	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	98	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	96	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	55
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	32	4
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	4	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	131	113
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,507	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	881	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	276	291
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	81
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	69	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	96	110
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	17	1
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	4	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	67
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	511	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	50	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	273	289
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	39	38
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	29	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	55
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	15	3
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	0	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 52	$ 46

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,361	$ 1,306
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	611	732
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	383	367
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	221	28
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	53	68
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	38
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	53	73
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	720	676
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	313	331
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	252	238
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	104	25
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	29	39
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	43
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	641	630
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	298	401
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	131	129
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	117	3
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24	29
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	38
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 31	$ 30

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - IPL [Member] $ in Millions	Sep. 30, 2021USD ($)
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	$ 110
Receivables Sold [Member]
Receivables [Line Items]
Available capacity	60
Receivables Sold [Member] | Financial Asset, Past Due
Receivables [Line Items]
Outstanding receivables past due	$ 19

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Maximum [Member]
Receivables [Line Items]
Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 110	$ 1	$ 110	$ 96
Average [Member]
Receivables [Line Items]
Average outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 65	$ 1	$ 52	$ 12

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Receivables [Line Items]
Fair value of deferred proceeds	$ 164	$ 188
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	164	188
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	145	114
Unbilled utility revenues	83	92
Receivables sold to third party	228	206
Less: cash proceeds	50	1
Deferred proceeds	178	205
Less: allowance for expected credit losses	14	17
Fair value of deferred proceeds	$ 164	$ 188

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Receivables [Line Items]
Collections	$ 607	$ 561	$ 1,589	$ 1,555
Write-offs, net of recoveries	$ 4	$ 1	$ 7	$ 4

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (13)	$ (15)	$ (47)	$ (46)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(12)	(11)	(34)	(36)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (1)	$ (4)	$ (13)	$ (10)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	9 Months Ended
	Sep. 30, 2021shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2021 (in shares)	249,868,415
Shareowner Direct Plan (in shares)	378,823
Equity-based compensation plans (in shares)	113,549
Shares outstanding, September 30, 2021 (in shares)	250,360,787

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 5,688
Beginning balance	$ 6,019	$ 5,748	5,888	$ 5,405
Net income attributable to common shareowners	256	246	571	550
Net income	259	249	579	558
Common stock dividends	(101)	(94)	(304)	(281)
Equity forward settlements and Shareowner Direct Plan issuances	6	6	22	241
Equity-based compensation plans and other	5	3	8	5
Adoption of new accounting standard, net of tax	(3,261)		(3,261)		$ (2,994)
Other comprehensive loss, net of tax				(2)
Ending balance	5,985		5,985
Ending balance	$ 6,185	$ 5,909	$ 6,185	$ 5,909
Common stock dividends (in dollars per share)	$ 0.4025	$ 0.38	$ 1.2075	$ 1.14
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 2	$ 2	$ 2
Equity forward settlements and Shareowner Direct Plan issuances			1
Ending balance	3	2	3	2
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,722	2,683	2,704	2,446
Equity forward settlements and Shareowner Direct Plan issuances	6	6	21	241
Equity-based compensation plans and other	5	4	8	6
Ending balance	2,733	2,693	2,733	2,693
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,106	2,874	2,994	2,766
Net income attributable to common shareowners	256	246	571	550
Common stock dividends	(101)	(94)	(304)	(281)
Ending balance	3,261	3,026	3,261	3,026
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(1)	(1)	(1)	1
Other comprehensive loss, net of tax				(2)
Ending balance	(1)	(1)	(1)	(1)
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(11)	(10)	(11)	(10)
Equity-based compensation plans and other		(1)		(1)
Ending balance	(11)	(11)	(11)	(11)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,764
Beginning balance	3,979	3,671	3,964	3,472
Net income attributable to common shareowners	157	148	322	290
Net income	160	151	330	298
Common stock dividends	(101)	(59)	(301)	(177)
Adoption of new accounting standard, net of tax	(1,000)		(1,000)		(979)
Capital contributions from parent		170	50	345
Ending balance	3,835		3,835
Ending balance	4,035	3,930	4,035	3,930
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33	33	33
Ending balance	33	33	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,802	2,523	2,752	2,348
Capital contributions from parent		170	50	345
Ending balance	2,802	2,693	2,802	2,693
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	944	915	979	891
Net income attributable to common shareowners	157	148	322	290
Common stock dividends	(101)	(59)	(301)	(177)
Ending balance	1,000	1,004	1,000	1,004
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			2,478
Beginning balance	2,725	2,452	2,478	2,364
Net income	93	73	215	220
Common stock dividends	(41)	(43)	(126)	(127)
Adoption of new accounting standard, net of tax	(1,042)		(1,042)		$ (953)
Capital contributions from parent	35		245	25
Ending balance	2,812		2,812
Ending balance	2,812	2,482	2,812	2,482
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66	66	66
Ending balance	66	66	66	66
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,669	1,459	1,459	1,434
Capital contributions from parent	35		245	25
Ending balance	1,704	1,459	1,704	1,459
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	990	927	953	864
Net income	93	73	215	220
Common stock dividends	(41)	(43)	(126)	(127)
Ending balance	$ 1,042	$ 957	$ 1,042	$ 957
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)

Preferred Stock (Narrative) (De

Preferred Stock (Narrative) (Details) - IPL [Member] $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)shares
Class of Stock [Line Items]
Preferred shares outstanding (in shares) | shares	8,000,000
Preferred stock series, percent	5.10%
Cumulative preferred stock | $	$ 200

Debt (Narrative) (Details)

Debt (Narrative) (Details) $ in Millions	Sep. 30, 2021USD ($)
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	500
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	100
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	400
Debentures | 1.95% debenture, due 2031 | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	1.95%

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Sep. 30, 2021USD ($)
Debt [Line Items]
Amount outstanding	$ 316
Weighted average interest rates	0.20%
Available credit facility capacity	$ 684
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	100
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 3
Weighted average interest rates	0.10%
Available credit facility capacity	$ 397

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 648	$ 422	$ 648	$ 463
Average amount outstanding (based on daily outstanding balances)	$ 560	$ 252	$ 479	$ 252
Weighted average interest rates	0.20%	0.20%	0.20%	1.10%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 8	$ 0	$ 19	$ 8
Average amount outstanding (based on daily outstanding balances)	$ 0	0	$ 0	$ 0
Weighted average interest rates	0.20%		0.20%	0.50%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 320	139	$ 320	$ 212
Average amount outstanding (based on daily outstanding balances)	$ 221	$ 83	$ 196	$ 86
Weighted average interest rates	0.10%	0.20%	0.10%	1.20%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,024	$ 920	$ 2,742	$ 2,599
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	939	852	2,357	2,257
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	348	328	868	845
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	232	210	579	556
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	265	241	677	648
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	47	142	127
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39	26	91	81
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	50	42	289	253
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	22	162	146
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	85	70
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2	11	8
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	8	31	29
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	36	32
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8	27	27
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2	9	5
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	16	60	57
Non-utility and Other [Member] | Travero and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	16	60	57
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	599	553	1,543	1,504
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	555	519	1,343	1,332
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	207	189	488	472
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	160	142	385	371
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	158	149	386	384
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18	17	44	44
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	22	40	61
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31	24	165	141
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	12	90	79
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	6	47	38
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	1	8	5
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	5	20	19
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	35	31
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8	27	27
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2	8	4
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	403	351	1,139	1,038
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	384	333	1,014	925
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	141	139	380	373
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72	68	194	185
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	107	92	291	264
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37	30	98	83
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	4	51	20
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	18	124	112
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	72	67
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	4	38	32
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	3	3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	3	11	10
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	1
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 1	$ 1

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Effective Tax Rate [Line Items]
Overall income tax rate	(9.00%)	(9.00%)	(13.00%)	(9.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(8.00%)	(14.00%)	(11.00%)	(14.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(19.00%)	(7.00%)	(24.00%)	(8.00%)

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2021USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 170
Tax credits, carryforward amount	547
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	157
Tax credits, carryforward amount	339
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
Tax credits, carryforward amount	186
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	592
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	24
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 7
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	$ 4
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 3
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	491,406

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 8	$ 8
Interest cost	9	10	26	32
Expected return on plan assets	(17)	(17)	(51)	(52)
Amortization of prior service credit	(1)	0	(1)	0
Amortization of actuarial loss	10	9	29	26
Settlement losses	0	0	0	4
Total	3	5	11	18
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	3
Interest cost	1	2	3	5
Expected return on plan assets	(1)	(1)	(3)	(4)
Amortization of prior service credit	0	0	0	0
Amortization of actuarial loss	1	0	3	2
Settlement losses	0	0	0	0
Total	2	2	6	6
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2	5	5
Interest cost	4	5	12	15
Expected return on plan assets	(8)	(8)	(24)	(24)
Amortization of actuarial loss	5	4	13	11
Total	2	3	6	7
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	1	1	2	2
Expected return on plan assets	(1)	(1)	(3)	(3)
Amortization of actuarial loss	0	0	1	1
Total	0	0	1	1
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	3
Interest cost	3	5	11	14
Expected return on plan assets	(8)	(8)	(23)	(23)
Amortization of actuarial loss	5	4	14	12
Total	1	2	5	6
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0	1	1
Interest cost	0	1	1	2
Expected return on plan assets	0	(1)	0	(1)
Amortization of actuarial loss	1	1	2	2
Total	$ 2	$ 1	$ 4	$ 4

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Compensation expense	$ 4	$ 5	$ 9	$ 10
Income tax benefits	1	1	3	3
IPL [Member]
Compensation expense	2	3	5	6
Income tax benefits	0	1	1	2
WPL [Member]
Compensation expense	2	2	4	4
Income tax benefits	$ 0	$ 0	$ 1	$ 1

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	73,112
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	73,112
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.66
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	80,152
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.65

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 251
Revisions in estimated cash flows	37
Liabilities settled	(10)
Liabilities incurred	1
Accretion expense	6
Balance, September 30	285
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	177
Revisions in estimated cash flows	32
Liabilities settled	(8)
Liabilities incurred	0
Accretion expense	4
Balance, September 30	$ 205

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	9 Months Ended
	Sep. 30, 2021DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	13,265
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	4,014
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	9,251
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	189,332
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	103,859
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	85,473
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,280
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	1,807
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	2,473
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,654
Diesel Fuel (Gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	0
Diesel Fuel (Gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,654

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 158	$ 24
Non-current derivative assets	78	10
Current derivative liabilities	3	9
Non-current derivative liabilities	1	16
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	72	20
Non-current derivative assets	43	9
Current derivative liabilities	3	3
Non-current derivative liabilities	1	9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	86	4
Non-current derivative assets	35	1
Current derivative liabilities	0	6
Non-current derivative liabilities	$ 0	$ 7

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets:
Money market fund investments	$ 9	$ 44
Deferred proceeds	164	188
Liabilities:
Long-term debt (incl. current maturities)	8,084	8,109
IPL [Member]
Assets:
Money market fund investments	9	44
Deferred proceeds	164	188
Liabilities:
Long-term debt (incl. current maturities)	3,849	4,021
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,869	2,690
Commodity Contracts [Member]
Assets:
Derivatives	236	34
Liabilities:
Derivatives	4	25
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	115	29
Liabilities:
Derivatives	4	12
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	121	5
Liabilities:
Derivatives	0	13
Level 1 [Member]
Assets:
Money market fund investments	9	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	9	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)	8,083	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)	3,849	4,021
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,869	2,690
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	207	5
Liabilities:
Derivatives	4	25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	96	3
Liabilities:
Derivatives	4	12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	111	2
Liabilities:
Derivatives	0	13
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	164	188
Liabilities:
Long-term debt (incl. current maturities)	1	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	164	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	29	29
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	19	26
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	10	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	9	44
Deferred proceeds	164	188
Liabilities:
Long-term debt (incl. current maturities)	7,075	6,777
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	9	44
Deferred proceeds	164	188
Liabilities:
Long-term debt (incl. current maturities)	3,347	3,345
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,429	2,130
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	236	34
Liabilities:
Derivatives	4	25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	115	29
Liabilities:
Derivatives	4	12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	121	5
Liabilities:
Derivatives	$ 0	$ 13

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 39	$ 36	$ 29	$ 21
Total net gains (losses) included in changes in net assets (realized/unrealized)	5	0	6	8
Transfers out of Level 3	(8)	0	(8)	0
Purchases			21	14
Sales	0	(1)	0	(1)
Settlements	(7)	(5)	(19)	(12)
Ending balance	29	30	29	30
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	5	(1)	6	8
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	30	32	26	18
Total net gains (losses) included in changes in net assets (realized/unrealized)	2	(1)	0	7
Transfers out of Level 3	(8)	0	(8)	0
Purchases			16	11
Sales	0	(1)	0	(1)
Settlements	(5)	(4)	(15)	(9)
Ending balance	19	26	19	26
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	2	(1)	0	7
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	154	194	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	10	7	(24)	13
Ending balance	164	201	164	201
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	0	0	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	154	194	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	10	7	(24)	13
Ending balance	164	201	164	201
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 29	$ 39	$ 29	$ 30	$ 36	$ 21
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	7		18
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	22		11
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	19	$ 30	26	$ 26	$ 32	$ 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	5		17
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	14		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	2		1
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 8		$ 2

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,201
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	639
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	538
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	95
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	93
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	67
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	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,201
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	639
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	538
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	985
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	514
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	471
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	82
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	54
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	28
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	134
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	71
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 39

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 12
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	6
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	24
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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,024	$ 920	$ 2,742	$ 2,599
Operating income (loss)	289	272	663	628
Net income attributable to common shareowners	256	246	571	550
Net income	259	249	579	558
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	599	553	1,543	1,504
Operating income (loss)	180	162	394	347
Net income attributable to common shareowners	157	148	322	290
Net income	160	151	330	298
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	403	351	1,139	1,038
Operating income (loss)	100	89	245	255
Net income	93	73	215	220
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	939	852	2,357	2,257
Operating income (loss)	290	251	601	549
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	555	519	1,343	1,332
Operating income (loss)	186	159	365	308
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	384	333	1,014	925
Operating income (loss)	104	92	236	241
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	50	42	289	253
Operating income (loss)	(5)	(1)	42	48
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	31	24	165	141
Operating income (loss)	(3)	1	30	34
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	19	18	124	112
Operating income (loss)	(2)	(2)	12	14
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	13	10	36	32
Operating income (loss)	(5)	1	(4)	5
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	13	10	35	31
Operating income (loss)	(3)	2	(1)	5
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	1	1
Operating income (loss)	(2)	(1)	(3)	0
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	1,002	904	2,682	2,542
Operating income (loss)	280	251	639	602
Net income attributable to common shareowners	250	221	537	510
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	22	16	60	57
Operating income (loss)	9	21	24	26
Net income attributable to common shareowners	$ 6	$ 25	$ 34	$ 40

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
ATC LLC [Member] | WPL Owed ATC LLC [Member] | Equity Method Investee [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 8	$ 9

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 50	$ 53	$ 138	$ 134
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	37	41	113	108
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	4	10	9	35
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	16	0	23	4
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	105	110	347	248
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 24	$ 39	$ 71	$ 79

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 109	$ 110
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 80	$ 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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 29	$ 27	$ 91	$ 80
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 4	$ 2	$ 13	$ 8