Interstate Power & Light (IPLDP) 10-Q 6 Aug 21 2021 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	6 Months Ended
	Jun. 30, 2021shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 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	250,257,856
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
IPL [Member]
Entity Information [Line Items]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Incorporation, State or Country Code	IA
Entity Address, Address Line One	Alliant Energy Tower
Entity Address, City or Town	Cedar Rapids
Entity Address, State or Province	IA
Entity Address, Postal Zip Code	52401
City Area Code	319
Local Phone Number	786-4411
Entity File Number	1-4117
Entity Tax Identification Number	42-0331370
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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues:
Electric utility	$ 717	$ 675	$ 1,418	$ 1,405
Gas utility	69	59	239	211
Other utility	10	10	23	22
Non-utility	21	19	38	41
Total revenues	817	763	1,718	1,679
Operating expenses:
Electric production fuel and purchased power	138	164	271	348
Electric transmission service	121	72	255	194
Cost of gas sold	31	21	131	106
Other operation and maintenance	160	159	306	322
Depreciation and amortization	165	152	329	298
Taxes other than income taxes	26	27	52	55
Total operating expenses	641	595	1,344	1,323
Operating income	176	168	374	356
Other (income) and deductions:
Interest expense	69	70	138	139
Equity income from unconsolidated investments, net	(19)	(18)	(34)	(31)
Allowance for funds used during construction	(5)	(15)	(9)	(38)
Other	2	3	4	4
Total other (income) and deductions	47	40	99	74
Income before income taxes	129	128	275	282
Income tax benefit	(17)	(8)	(45)	(27)
Net income	146	136	320	309
Preferred dividend requirements of Interstate Power and Light Company	2	2	5	5
Net income attributable to common shareowners	$ 144	$ 134	$ 315	$ 304
Weighted average number of common shares outstanding:
Basic (in shares)	250.2	249.6	250.1	247
Diluted (in shares)	250.6	249.8	250.5	247.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.58	$ 0.54	$ 1.26	$ 1.23
Diluted (in dollars per share)	$ 0.57	$ 0.54	$ 1.26	$ 1.23
IPL [Member]
Revenues:
Electric utility	$ 402	$ 388	$ 788	$ 813
Gas utility	43	34	134	117
Other utility	10	10	22	21
Total revenues	455	432	944	951
Operating expenses:
Electric production fuel and purchased power	55	96	114	202
Electric transmission service	79	35	171	119
Cost of gas sold	22	13	72	57
Other operation and maintenance	81	97	158	184
Depreciation and amortization	93	89	187	175
Taxes other than income taxes	14	14	28	29
Total operating expenses	344	344	730	766
Operating income	111	88	214	185
Other (income) and deductions:
Interest expense	34	35	69	69
Allowance for funds used during construction	(3)	(5)	(5)	(15)
Other	2	0	2	2
Total other (income) and deductions	33	30	66	56
Income before income taxes	78	58	148	129
Income tax benefit	(10)	(4)	(22)	(18)
Net income	88	62	170	147
Preferred dividend requirements of Interstate Power and Light Company	2	2	5	5
Net income attributable to common shareowners	86	60	165	142
WPL [Member]
Revenues:
Electric utility	315	287	630	592
Gas utility	26	25	105	94
Other utility	0	0	1	1
Total revenues	341	312	736	687
Operating expenses:
Electric production fuel and purchased power	84	67	158	145
Electric transmission service	42	37	84	75
Cost of gas sold	9	8	59	49
Other operation and maintenance	69	53	128	107
Depreciation and amortization	70	62	139	121
Taxes other than income taxes	12	13	23	24
Total operating expenses	286	240	591	521
Operating income	55	72	145	166
Other (income) and deductions:
Interest expense	26	27	52	52
Allowance for funds used during construction	(2)	(10)	(4)	(23)
Other	0	2	1	2
Total other (income) and deductions	24	19	49	31
Income before income taxes	31	53	96	135
Income tax benefit	(7)	(5)	(26)	(12)
Net income	$ 38	$ 58	$ 122	$ 147

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 15	$ 54
Accounts receivable, less allowance for expected credit losses	377	412
Production fuel, at weighted average cost	57	66
Gas stored underground, at weighted average cost	32	46
Materials and supplies, at weighted average cost	119	105
Regulatory assets	95	81
Other	204	123
Total current assets	899	887
Property, plant and equipment, net	14,540	14,336
Investments:
ATC Holdings	336	331
Other	170	154
Total investments	506	485
Other assets:
Regulatory assets	1,900	1,929
Deferred charges and other	94	73
Total other assets	1,994	2,002
Total assets	17,939	17,710
Current liabilities:
Current maturities of long-term debt	308	8
Commercial paper	535	389
Accounts payable	392	377
Regulatory liabilities	174	249
Other	230	274
Total current liabilities	1,639	1,297
Long-term debt, net (excluding current portion)	6,468	6,769
Other liabilities:
Deferred tax liabilities	1,865	1,814
Regulatory liabilities	1,080	1,057
Pension and other benefit obligations	477	511
Other	391	374
Total other liabilities	3,813	3,756
Commitments and contingencies (Note 13)
Common equity:
Common stock	3	2
Additional paid-in capital	2,722	2,704
Retained earnings	3,106	2,994
Accumulated other comprehensive loss	(1)	(1)
Shares in deferred compensation trust - 372,337 and 380,542 shares at a weighted average cost of $29.65 and $28.73 per share	(11)	(11)
Total common equity	5,819	5,688
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	6,019	5,888
Total liabilities and equity	17,939	17,710
IPL [Member]
Current assets:
Cash and cash equivalents	11	50
Accounts receivable, less allowance for expected credit losses	182	210
Income tax refunds receivable	15	26
Production fuel, at weighted average cost	38	48
Gas stored underground, at weighted average cost	12	20
Materials and supplies, at weighted average cost	72	63
Regulatory assets	72	52
Other	53	27
Total current assets	455	496
Property, plant and equipment, net	7,907	7,889
Other assets:
Regulatory assets	1,416	1,431
Deferred charges and other	47	33
Total other assets	1,463	1,464
Total assets	9,825	9,849
Current liabilities:
Accounts payable	126	162
Regulatory liabilities	64	103
Other	180	182
Total current liabilities	370	447
Long-term debt, net (excluding current portion)	3,346	3,345
Other liabilities:
Deferred tax liabilities	1,054	1,035
Regulatory liabilities	583	573
Pension and other benefit obligations	171	186
Other	322	299
Total other liabilities	2,130	2,093
Commitments and contingencies (Note 13)
Common equity:
Common stock	33	33
Additional paid-in capital	2,802	2,752
Retained earnings	944	979
Total common equity	3,779	3,764
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,979	3,964
Total liabilities and equity	9,825	9,849
WPL [Member]
Current assets:
Cash and cash equivalents	3	3
Accounts receivable, less allowance for expected credit losses	182	192
Production fuel, at weighted average cost	19	18
Gas stored underground, at weighted average cost	20	26
Materials and supplies, at weighted average cost	44	40
Regulatory assets	23	29
Other	92	54
Total current assets	383	362
Property, plant and equipment, net	6,203	6,022
Other assets:
Regulatory assets	484	498
Deferred charges and other	47	30
Total other assets	531	528
Total assets	7,117	6,912
Current liabilities:
Commercial paper	192	257
Accounts payable	203	154
Regulatory liabilities	110	146
Other	94	117
Total current liabilities	599	674
Long-term debt, net (excluding current portion)	2,131	2,130
Other liabilities:
Deferred tax liabilities	730	702
Regulatory liabilities	497	484
Finance lease obligations - Sheboygan Falls Energy Facility	37	42
Pension and other benefit obligations	205	222
Other	193	180
Total other liabilities	1,662	1,630
Commitments and contingencies (Note 13)
Common equity:
Common stock	66	66
Additional paid-in capital	1,669	1,459
Retained earnings	990	953
Total common equity	2,725	2,478
Total equity	2,725	2,478
Total liabilities and equity	$ 7,117	$ 6,912

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 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)	250,257,856	249,868,415
Shares in deferred compensation trust (in shares)	372,337	380,542
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 29.65	$ 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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 320	$ 309
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	329	298
Deferred tax benefit and tax credits	(42)	(29)
Equity component of allowance for funds used during construction	(6)	(27)
Other	8	27
Other changes in assets and liabilities:
Accounts receivable	(265)	(198)
Derivative assets	(68)	(16)
Regulatory liabilities	(69)	(63)
Deferred income taxes	93	82
Pension and other benefit obligations	(34)	(34)
Other	(59)	(30)
Net cash flows from operating activities	207	319
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(426)	(584)
Other construction and acquisition expenditures	(32)	(24)
Cash receipts on sold receivables	295	210
Other	(27)	6
Net cash flows from (used for) investing activities	(190)	(392)
Cash flows from (used for) financing activities:
Common stock dividends	(203)	(187)
Proceeds from issuance of common stock, net	15	235
Proceeds from issuance of long-term debt	0	1,050
Payments to retire long-term debt	(4)	(654)
Net change in commercial paper	146	(152)
Other	(11)	(28)
Net cash flows from (used for) financing activities	(57)	264
Net increase (decrease) in cash, cash equivalents and restricted cash	(40)	191
Cash, cash equivalents and restricted cash at beginning of period	56	18
Cash, cash equivalents and restricted cash at end of period	16	209
Supplemental cash flows information:
Interest	(137)	(138)
Income taxes, net	(1)	(5)
Significant non-cash investing and financing activities:
Accrued capital expenditures	139	208
Beneficial interest obtained in exchange for securitized accounts receivable	154	194
IPL [Member]
Cash flows from operating activities:
Net income	170	147
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	187	175
Deferred tax benefit and tax credits	(11)	(21)
Other	(2)	(6)
Other changes in assets and liabilities:
Accounts receivable	(270)	(219)
Derivative assets	(27)	(15)
Accounts payable	1	26
Regulatory liabilities	(36)	0
Deferred income taxes	30	26
Other	(24)	(36)
Net cash flows from operating activities	18	77
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(191)	(310)
Cash receipts on sold receivables	295	210
Other	(6)	(25)
Net cash flows from (used for) investing activities	98	(125)
Cash flows from (used for) financing activities:
Common stock dividends	(200)	(118)
Capital contributions from parent	50	175
Proceeds from issuance of long-term debt	0	400
Payments to retire long-term debt	0	(200)
Other	(5)	(15)
Net cash flows from (used for) financing activities	(155)	242
Net increase (decrease) in cash, cash equivalents and restricted cash	(39)	194
Cash, cash equivalents and restricted cash at beginning of period	50	9
Cash, cash equivalents and restricted cash at end of period	11	203
Supplemental cash flows information:
Interest	(69)	(72)
Income taxes, net	27	7
Significant non-cash investing and financing activities:
Accrued capital expenditures	32	94
Beneficial interest obtained in exchange for securitized accounts receivable	154	194
WPL [Member]
Cash flows from operating activities:
Net income	122	147
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	139	121
Deferred tax benefit and tax credits	(35)	(12)
Other	10	(7)
Other changes in assets and liabilities:
Accounts receivable	9	23
Derivative assets	(41)	(1)
Regulatory liabilities	(33)	(63)
Deferred income taxes	63	53
Other	(34)	(5)
Net cash flows from operating activities	200	256
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(235)	(274)
Other	(18)	14
Net cash flows from (used for) investing activities	(253)	(260)
Cash flows from (used for) financing activities:
Common stock dividends	(85)	(84)
Capital contributions from parent	210	25
Proceeds from issuance of long-term debt	0	350
Payments to retire long-term debt	0	(150)
Net change in commercial paper	(65)	(130)
Other	(7)	(8)
Net cash flows from (used for) financing activities	53	3
Net increase (decrease) in cash, cash equivalents and restricted cash	0	(1)
Cash, cash equivalents and restricted cash at beginning of period	3	4
Cash, cash equivalents and restricted cash at end of period	3	3
Supplemental cash flows information:
Interest	(52)	(50)
Income taxes, net	(27)	1
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 104	$ 114

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 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 Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 six months ended June 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 $475 million in aggregate as of June 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 June 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 June 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 Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 six months ended June 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 $475 million in aggregate as of June 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 June 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 June 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 Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 six months ended June 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 $475 million in aggregate as of June 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 June 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 June 30, 2021.

Regulatory Matters

Regulatory Matters	6 Months Ended
	Jun. 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of June 30, 2021, IPL’s cumulative under-collection of these natural gas costs was $14 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $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 six months ended June 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of June 30, 2021, IPL’s cumulative under-collection of these natural gas costs was $14 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $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 six months ended June 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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527 Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of June 30, 2021, IPL’s cumulative under-collection of these natural gas costs was $14 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $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 six months ended June 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	6 Months Ended
	Jun. 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 June 30, 2021, IPL had $65 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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $65 $110 $96 Average outstanding aggregate cash proceeds 61 11 46 17 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2021 December 31, 2020 Customer accounts receivable $125 $114 Unbilled utility revenues 88 92 Receivables sold to third party 213 206 Less: cash proceeds 45 1 Deferred proceeds 168 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $154 $188 As of June 30, 2021, outstanding receivables past due under the Receivables Agreement were $15 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Collections $453 $453 $982 $994 Write-offs, net of recoveries 1 1 3 3
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. 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 June 30, 2021, IPL had $65 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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $65 $110 $96 Average outstanding aggregate cash proceeds 61 11 46 17 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2021 December 31, 2020 Customer accounts receivable $125 $114 Unbilled utility revenues 88 92 Receivables sold to third party 213 206 Less: cash proceeds 45 1 Deferred proceeds 168 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $154 $188 As of June 30, 2021, outstanding receivables past due under the Receivables Agreement were $15 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Collections $453 $453 $982 $994 Write-offs, net of recoveries 1 1 3 3

Investments

Investments	6 Months Ended
	Jun. 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 six months ended June 30 was as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC Holdings ($11) ($14) ($22) ($25) Other (8) (4) (12) (6) ($19) ($18) ($34) ($31)

Common Equity

Common Equity	6 Months Ended
	Jun. 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 275,892 Equity-based compensation plans 113,549 Shares outstanding, June 30, 2021 250,257,856 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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452
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 275,892 Equity-based compensation plans 113,549 Shares outstanding, June 30, 2021 250,257,856 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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452
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 275,892 Equity-based compensation plans 113,549 Shares outstanding, June 30, 2021 250,257,856 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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452

Debt

Debt	6 Months Ended
	Jun. 30, 2021
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%
IPL [Member]
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%
WPL [Member]
Debt [Line Items]
Debt	DEBT Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%

Revenues

Revenues	6 Months Ended
	Jun. 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 June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687

Income Taxes

Income Taxes	6 Months Ended
	Jun. 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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%) Deferred Tax Assets and Liabilities - Carryforwards - At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182
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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%) Deferred Tax Assets and Liabilities - Carryforwards - At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182
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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%) Deferred Tax Assets and Liabilities - Carryforwards - At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182

Benefit Plans

Benefit Plans	6 Months Ended
	Jun. 30, 2021
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1 As of June 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $4 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of June 30, 2021, 453,489 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1 As of June 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $4 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of June 30, 2021, 453,489 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1 As of June 30, 2021, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $4 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the six months ended June 30, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61 As of June 30, 2021, 453,489 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	6 Months Ended
	Jun. 30, 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 six months ended June 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 32 26 Liabilities settled (4) (3) Accretion expense 4 3 Balance, June 30 $283 $203
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 six months ended June 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 32 26 Liabilities settled (4) (3) Accretion expense 4 3 Balance, June 30 $283 $203

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2021
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7 During the three and six months ended June 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 June 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
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7 During the three and six months ended June 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 June 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
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7 During the three and six months ended June 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 June 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

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30 2021 2020 2021 2020 Beginning balance, April 1 $15 $14 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 8 12 — — Purchases 21 14 — — Settlements (a) (5) (4) 47 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $8 $12 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 1 9 — — Purchases 21 14 — — Settlements (a) (12) (8) (34) 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $1 $9 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2021 2020 2021 2020 Beginning balance, April 1 $14 $13 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 4 11 — — Purchases 16 11 — — Settlements (a) (4) (3) 47 6 Ending balance, June 30 $30 $32 $154 $194 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 June 30 $4 $11 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 9 — — Purchases 16 11 — — Settlements (a) (10) (6) (34) 6 Ending balance, June 30 $30 $32 $154 $194 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 ($2) $9 $— $— (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 June 30, 2021 $13 $26 $13 $17 $— $9 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30 2021 2020 2021 2020 Beginning balance, April 1 $15 $14 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 8 12 — — Purchases 21 14 — — Settlements (a) (5) (4) 47 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $8 $12 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 1 9 — — Purchases 21 14 — — Settlements (a) (12) (8) (34) 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $1 $9 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2021 2020 2021 2020 Beginning balance, April 1 $14 $13 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 4 11 — — Purchases 16 11 — — Settlements (a) (4) (3) 47 6 Ending balance, June 30 $30 $32 $154 $194 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 June 30 $4 $11 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 9 — — Purchases 16 11 — — Settlements (a) (10) (6) (34) 6 Ending balance, June 30 $30 $32 $154 $194 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 ($2) $9 $— $— (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 June 30, 2021 $13 $26 $13 $17 $— $9 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30 2021 2020 2021 2020 Beginning balance, April 1 $15 $14 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 8 12 — — Purchases 21 14 — — Settlements (a) (5) (4) 47 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $8 $12 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 1 9 — — Purchases 21 14 — — Settlements (a) (12) (8) (34) 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $1 $9 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2021 2020 2021 2020 Beginning balance, April 1 $14 $13 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 4 11 — — Purchases 16 11 — — Settlements (a) (4) (3) 47 6 Ending balance, June 30 $30 $32 $154 $194 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 June 30 $4 $11 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 9 — — Purchases 16 11 — — Settlements (a) (10) (6) (34) 6 Ending balance, June 30 $30 $32 $154 $194 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 ($2) $9 $— $— (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 June 30, 2021 $13 $26 $13 $17 $— $9 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies

Commitments And Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At June 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $25 million and $22 million, respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 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 June 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 $74 million as of June 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 June 30, 2021 and December 31, 2020. NOTE 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At June 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 June 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 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At June 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $25 million and $22 million, respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 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 June 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 $74 million as of June 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 June 30, 2021 and December 31, 2020. NOTE 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At June 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 June 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 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of solar generation. At June 30, 2021, Alliant Energy’s and WPL’s minimum future commitments for these projects were $25 million and $22 million, respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021. NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 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 June 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 $74 million as of June 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 June 30, 2021 and December 31, 2020. NOTE 13(d) Environmental Matters - Manufactured Gas Plant (MGP) Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At June 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 June 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	6 Months Ended
	Jun. 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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147
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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147
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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147

Related Parties

Related Parties	6 Months Ended
	Jun. 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 six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC billings to WPL $30 $25 $62 $53 WPL billings to ATC 6 3 9 6 WPL owed ATC net amounts of $9 million as of June 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 six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $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 six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC billings to WPL $30 $25 $62 $53 WPL billings to ATC 6 3 9 6 WPL owed ATC net amounts of $9 million as of June 30, 2021 and $9 million as of December 31, 2020.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	6 Months Ended
	Jun. 30, 2021
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 $475 million in aggregate as of June 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 June 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 June 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 Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 $475 million in aggregate as of June 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 June 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 June 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 Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 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 $475 million in aggregate as of June 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 June 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 June 30, 2021.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	6 Months Ended
	Jun. 30, 2021
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $630
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $630
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $914 $890 $865 $843 $49 $47 Pension and OPEB costs 559 580 281 291 278 289 Asset retirement obligations 123 119 85 81 38 38 Assets retired early 103 113 72 77 31 36 IPL’s DAEC PPA amendment 102 110 102 110 — — WPL’s Western Wisconsin gas distribution expansion investments 54 55 — — 54 55 Derivatives 3 26 2 13 1 13 Other 137 117 81 68 56 49 $1,995 $2,010 $1,488 $1,483 $507 $527
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $661 $732 $322 $331 $339 $401 Cost of removal obligations 373 367 245 238 128 129 Derivatives 81 28 40 25 41 3 Electric transmission cost recovery 48 68 23 39 25 29 WPL’s West Riverside liquidated damages 40 38 — — 40 38 Other 51 73 17 43 34 30 $1,254 $1,306 $647 $676 $607 $630

Receivables (Tables)

Receivables (Tables)	6 Months Ended
	Jun. 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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $65 $110 $96 Average outstanding aggregate cash proceeds 61 11 46 17
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2021 December 31, 2020 Customer accounts receivable $125 $114 Unbilled utility revenues 88 92 Receivables sold to third party 213 206 Less: cash proceeds 45 1 Deferred proceeds 168 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $154 $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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Collections $453 $453 $982 $994 Write-offs, net of recoveries 1 1 3 3
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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Maximum outstanding aggregate cash proceeds $110 $65 $110 $96 Average outstanding aggregate cash proceeds 61 11 46 17
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2021 December 31, 2020 Customer accounts receivable $125 $114 Unbilled utility revenues 88 92 Receivables sold to third party 213 206 Less: cash proceeds 45 1 Deferred proceeds 168 205 Less: allowance for expected credit losses 14 17 Fair value of deferred proceeds $154 $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 six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 Collections $453 $453 $982 $994 Write-offs, net of recoveries 1 1 3 3

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 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 six months ended June 30 was as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC Holdings ($11) ($14) ($22) ($25) Other (8) (4) (12) (6) ($19) ($18) ($34) ($31)

Common Equity (Tables)

Common Equity (Tables)	6 Months Ended
	Jun. 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 275,892 Equity-based compensation plans 113,549 Shares outstanding, June 30, 2021 250,257,856
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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452
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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452
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 June 30, 2021 Beginning balance, March 31, 2021 $3 $2,712 $3,063 ($1) ($11) $200 $5,966 Net income attributable to Alliant Energy common shareowners 144 144 Common stock dividends ($0.4025 per share) (101) (101) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 3 3 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2 $2,674 $2,834 $2 ($10) $200 $5,702 Net income attributable to Alliant Energy common shareowners 134 134 Common stock dividends ($0.38 per share) (94) (94) Shareowner Direct Plan issuances 7 7 Equity-based compensation plans and other 2 2 Other comprehensive loss, net of tax (3) (3) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 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 Six Months Ended June 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 315 315 Common stock dividends ($0.805 per share) (203) (203) Shareowner Direct Plan issuances 1 14 15 Equity-based compensation plans and other 4 4 Ending balance, June 30, 2021 $3 $2,722 $3,106 ($1) ($11) $200 $6,019 Six Months Ended June 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 304 304 Common stock dividends ($0.76 per share) (187) (187) Equity forward settlements and Shareowner Direct Plan issuances 235 235 Equity-based compensation plans and other 2 2 Adoption of new accounting standard, net of tax (9) (9) Other comprehensive loss, net of tax (2) (2) Ending balance, June 30, 2020 $2 $2,683 $2,874 ($1) ($10) $200 $5,748 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $33 $2,752 $957 $200 $3,942 Net income available for common stock 86 86 Common stock dividends (99) (99) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33 $2,448 $914 $200 $3,595 Net income available for common stock 60 60 Common stock dividends (59) (59) Capital contributions from parent 75 75 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $33 $2,752 $979 $200 $3,964 Net income available for common stock 165 165 Common stock dividends (200) (200) Capital contributions from parent 50 50 Ending balance, June 30, 2021 $33 $2,802 $944 $200 $3,979 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 142 142 Common stock dividends (118) (118) Capital contributions from parent 175 175 Ending balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2021 Beginning balance, March 31, 2021 $66 $1,584 $995 $2,645 Net income 38 38 Common stock dividends (43) (43) Capital contributions from parent 85 85 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66 $1,459 $911 $2,436 Net income 58 58 Common stock dividends (42) (42) Ending balance, June 30, 2020 $66 $1,459 $927 $2,452 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2021 Beginning balance, December 31, 2020 $66 $1,459 $953 $2,478 Net income 122 122 Common stock dividends (85) (85) Capital contributions from parent 210 210 Ending balance, June 30, 2021 $66 $1,669 $990 $2,725 Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 147 147 Common stock dividends (84) (84) Capital contributions from parent 25 25 Ending balance, June 30, 2020 $66 $1,459 $927 $2,452

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 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): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%
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): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%
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): June 30, 2021 Alliant Energy IPL WPL Amount outstanding $535 $— $192 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $465 $250 $108 Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Maximum amount outstanding (based on daily outstanding balances) $571 $271 $19 $8 $232 $182 Average amount outstanding (based on daily outstanding balances) $452 $121 $1 $— $177 $9 Weighted average interest rates 0.2% 0.5% 0.2% 0.5% 0.1% 0.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $578 $463 $19 $8 $275 $212 Average amount outstanding (based on daily outstanding balances) $438 $252 $— $— $183 $88 Weighted average interest rates 0.2% 1.5% 0.2% 0.5% 0.1% 1.7%

Revenues (Tables)

Revenues (Tables)	6 Months Ended
	Jun. 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 June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $258 $251 $142 $136 $116 $115 Retail - commercial 175 163 115 109 60 54 Retail - industrial 210 197 116 114 94 83 Wholesale 47 40 15 13 32 27 Bulk power and other 27 24 14 16 13 8 Total Electric Utility 717 675 402 388 315 287 Gas Utility: Retail - residential 39 33 24 18 15 15 Retail - commercial 19 15 12 8 7 7 Retail - industrial 3 2 2 2 1 — Transportation/other 8 9 5 6 3 3 Total Gas Utility 69 59 43 34 26 25 Other Utility: Steam 9 9 9 9 — — Other utility 1 1 1 1 — — Total Other Utility 10 10 10 10 — — Non-Utility and Other: Transportation and other 21 19 — — — — Total Non-Utility and Other 21 19 — — — — Total revenues $817 $763 $455 $432 $341 $312 Alliant Energy IPL WPL Six Months Ended June 30 2021 2020 2021 2020 2021 2020 Electric Utility: Retail - residential $520 $517 $281 $283 $239 $234 Retail - commercial 347 346 225 229 122 117 Retail - industrial 412 407 228 235 184 172 Wholesale 87 80 26 27 61 53 Bulk power and other 52 55 28 39 24 16 Total Electric Utility 1,418 1,405 788 813 630 592 Gas Utility: Retail - residential 138 124 76 67 62 57 Retail - commercial 72 60 39 32 33 28 Retail - industrial 8 6 5 4 3 2 Transportation/other 21 21 14 14 7 7 Total Gas Utility 239 211 134 117 105 94 Other Utility: Steam 18 19 18 19 — — Other utility 5 3 4 2 1 1 Total Other Utility 23 22 22 21 1 1 Non-Utility and Other: Transportation and other 38 41 — — — — Total Non-Utility and Other 38 41 — — — — Total revenues $1,718 $1,679 $944 $951 $736 $687

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%)
Summary Of Tax Credit Carryforwards	At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182
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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%)
Summary Of Tax Credit Carryforwards	At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182
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, IPL’s and WPL’s overall effective income tax rates for the three and six months ended June 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, and increased production tax credits at IPL. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Overall income tax rate (13%) (6%) (16%) (10%) (13%) (7%) (15%) (14%) (23%) (9%) (27%) (9%)
Summary Of Tax Credit Carryforwards	At June 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 $322 $297 $3 State net operating losses 2021-2041 652 29 2 Federal tax credits 2022-2041 506 302 182

Benefit Plans (Tables)

Benefit Plans (Tables)	6 Months Ended
	Jun. 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 six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (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 six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (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 six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $3 $2 $6 $5 $1 $1 $2 $2 Interest cost 9 11 17 22 1 1 2 3 Expected return on plan assets (17) (17) (34) (35) (1) (1) (2) (3) Amortization of actuarial loss 9 8 19 17 1 1 2 2 Settlement losses (a) — — — 4 — — — — $4 $4 $8 $13 $2 $2 $4 $4 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $2 $2 $4 $3 $1 $1 $1 $1 Interest cost 4 5 8 10 — — 1 1 Expected return on plan assets (8) (8) (16) (16) (1) (1) (2) (2) Amortization of actuarial loss 4 3 8 7 1 1 1 1 $2 $2 $4 $4 $1 $1 $1 $1 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $1 $1 $2 $2 $— $1 $— $1 Interest cost 4 4 8 9 1 — 1 1 Expected return on plan assets (7) (7) (15) (15) — — — — Amortization of actuarial loss 4 4 9 8 — 1 1 1 $2 $2 $4 $4 $1 $2 $2 $3 (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 six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 2021 2020 Compensation expense $2 $2 $5 $5 $2 $2 $3 $3 $1 $1 $2 $2 Income tax benefits 1 1 2 2 1 1 1 1 1 1 1 1
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 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 72,774 $46.19 Performance restricted stock units 72,774 48.61 Restricted stock units 79,862 48.61

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	6 Months Ended
	Jun. 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 six months ended June 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 32 26 Liabilities settled (4) (3) Accretion expense 4 3 Balance, June 30 $283 $203
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 six months ended June 30, 2021 is as follows (in millions): Alliant Energy IPL Balance, January 1 $251 $177 Revisions in estimated cash flows 32 26 Liabilities settled (4) (3) Accretion expense 4 3 Balance, June 30 $283 $203

Derivative Instruments (Tables)

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2021
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 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 16,242 2021-2022 179,960 2021-2028 5,148 2021-2023 4,284 2021-2022 IPL 4,936 2021-2022 94,049 2021-2028 1,946 2021-2023 — — WPL 11,306 2021-2022 85,911 2021-2027 3,202 2021-2023 4,284 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 June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $77 $24 $41 $20 $36 $4 Non-current derivative assets 25 10 15 9 10 1 Current derivative liabilities 1 9 1 3 — 6 Non-current derivative liabilities 3 16 1 9 2 7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30 2021 2020 2021 2020 Beginning balance, April 1 $15 $14 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 8 12 — — Purchases 21 14 — — Settlements (a) (5) (4) 47 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $8 $12 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 1 9 — — Purchases 21 14 — — Settlements (a) (12) (8) (34) 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $1 $9 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2021 2020 2021 2020 Beginning balance, April 1 $14 $13 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 4 11 — — Purchases 16 11 — — Settlements (a) (4) (3) 47 6 Ending balance, June 30 $30 $32 $154 $194 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 June 30 $4 $11 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 9 — — Purchases 16 11 — — Settlements (a) (10) (6) (34) 6 Ending balance, June 30 $30 $32 $154 $194 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 ($2) $9 $— $— (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 June 30, 2021 $13 $26 $13 $17 $— $9 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30 2021 2020 2021 2020 Beginning balance, April 1 $15 $14 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 8 12 — — Purchases 21 14 — — Settlements (a) (5) (4) 47 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $8 $12 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $29 $21 $188 $188 Total net gains included in changes in net assets (realized/unrealized) 1 9 — — Purchases 21 14 — — Settlements (a) (12) (8) (34) 6 Ending balance, June 30 $39 $36 $154 $194 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 June 30 $1 $9 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2021 2020 2021 2020 Beginning balance, April 1 $14 $13 $107 $188 Total net gains included in changes in net assets (realized/unrealized) 4 11 — — Purchases 16 11 — — Settlements (a) (4) (3) 47 6 Ending balance, June 30 $30 $32 $154 $194 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 June 30 $4 $11 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2021 2020 2021 2020 Beginning balance, January 1 $26 $18 $188 $188 Total net gains (losses) included in changes in net assets (realized/unrealized) (2) 9 — — Purchases 16 11 — — Settlements (a) (10) (6) (34) 6 Ending balance, June 30 $30 $32 $154 $194 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 ($2) $9 $— $— (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 June 30, 2021 $13 $26 $13 $17 $— $9 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 June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 102 — 62 40 102 34 — 5 29 34 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 4 — 3 1 4 25 — 25 — 25 Long-term debt (incl. current maturities) 6,776 — 7,846 1 7,847 6,777 — 8,107 2 8,109 IPL June 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 $6 $6 $— $— $6 $44 $44 $— $— $44 Derivatives 56 — 25 31 56 29 — 3 26 29 Deferred proceeds 154 — — 154 154 188 — — 188 188 Liabilities: Derivatives 2 — 1 1 2 12 — 12 — 12 Long-term debt 3,346 — 3,880 — 3,880 3,345 — 4,021 — 4,021 WPL June 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 $46 $— $37 $9 $46 $5 $— $2 $3 $5 Liabilities: Derivatives 2 — 2 — 2 13 — 13 — 13 Long-term debt 2,131 — 2,593 — 2,593 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 June 30, 2021 $13 $26 $13 $17 $— $9 December 31, 2020 18 11 17 9 1 2

Commitments And Contingencies (

Commitments And Contingencies (Tables)	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At June 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 June 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 June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021.
MGP Site Estimated Future Costs And Recorded Liabilities	At June 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 June 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 June 30, 2021, related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $909 $456 $453 Coal 89 48 41 Other (a) 124 65 29 $1,122 $569 $523 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at June 30, 2021.

Segments Of Business (Tables)

Segments Of Business (Tables)	6 Months Ended
	Jun. 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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147
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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147
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 June 30, 2021 Revenues $717 $69 $10 $796 $21 $817 Operating income (loss) 164 3 (1) 166 10 176 Net income attributable to Alliant Energy common shareowners 124 20 144 Three Months Ended June 30, 2020 Revenues $675 $59 $10 $744 $19 $763 Operating income 152 7 1 160 8 168 Net income attributable to Alliant Energy common shareowners 118 16 134 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2021 Revenues $1,418 $239 $23 $1,680 $38 $1,718 Operating income 311 47 1 359 15 374 Net income attributable to Alliant Energy common shareowners 287 28 315 Six Months Ended June 30, 2020 Revenues $1,405 $211 $22 $1,638 $41 $1,679 Operating income 298 49 4 351 5 356 Net income attributable to Alliant Energy common shareowners 289 15 304 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $402 $43 $10 $455 Operating income 107 3 1 111 Net income available for common stock 86 Three Months Ended June 30, 2020 Revenues $388 $34 $10 $432 Operating income 82 5 1 88 Net income available for common stock 60 Six Months Ended June 30, 2021 Revenues $788 $134 $22 $944 Operating income 179 33 2 214 Net income available for common stock 165 Six Months Ended June 30, 2020 Revenues $813 $117 $21 $951 Operating income 149 33 3 185 Net income available for common stock 142 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2021 Revenues $315 $26 $— $341 Operating income (loss) 57 — (2) 55 Net income 38 Three Months Ended June 30, 2020 Revenues $287 $25 $— $312 Operating income 70 2 — 72 Net income 58 Six Months Ended June 30, 2021 Revenues $630 $105 $1 $736 Operating income (loss) 132 14 (1) 145 Net income 122 Six Months Ended June 30, 2020 Revenues $592 $94 $1 $687 Operating income 149 16 1 166 Net income 147

Related Parties (Tables)

Related Parties (Tables)	6 Months Ended
	Jun. 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 six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC billings to WPL $30 $25 $62 $53 WPL billings to ATC 6 3 9 6
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $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 six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2021 2020 2021 2020 2021 2020 2021 2020 Corporate Services billings $48 $44 $88 $81 $41 $35 $76 $67 Sales credited 4 10 5 25 6 2 7 4 Purchases billed 99 57 242 138 21 20 47 40
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2021 December 31, 2020 June 30, 2021 December 31, 2020 Net payables to Corporate Services $126 $110 $72 $73
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2021 2020 2021 2020 ATC billings to WPL $30 $25 $62 $53 WPL billings to ATC 6 3 9 6

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	Jun. 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	$ 475

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory Matters [Line Items]
Regulatory assets	$ 1,995	$ 2,010
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	1,488	$ 1,483
Deferred Fuel Costs | IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	$ 14

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 1,995	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	914	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	559	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	123	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	103	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	102	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	55
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	3	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	137	117
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,488	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	865	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	281	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	72	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	102	110
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	2	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	81	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	507	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	49	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	278	289
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	38	38
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	31	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	55
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	1	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 56	$ 49

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,254	$ 1,306
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	661	732
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	373	367
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	81	28
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48	68
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	38
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	51	73
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	647	676
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	322	331
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	245	238
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	25
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23	39
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	17	43
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	607	630
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	339	401
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	128	129
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	41	3
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	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	$ 34	$ 30

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - IPL [Member] $ in Millions	Jun. 30, 2021USD ($)
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	$ 110
Receivables Sold [Member]
Receivables [Line Items]
Available capacity	65
Receivables Sold [Member] | Financial Asset, Past Due
Receivables [Line Items]
Outstanding receivables past due	$ 15

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Maximum [Member]
Receivables [Line Items]
Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 110	$ 65	$ 110	$ 96
Average [Member]
Receivables [Line Items]
Average outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 61	$ 11	$ 46	$ 17

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Receivables [Line Items]
Fair value of deferred proceeds	$ 154	$ 188
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	154	188
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	125	114
Unbilled utility revenues	88	92
Receivables sold to third party	213	206
Less: cash proceeds	45	1
Deferred proceeds	168	205
Less: allowance for expected credit losses	14	17
Fair value of deferred proceeds	$ 154	$ 188

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Receivables [Line Items]
Collections	$ 453	$ 453	$ 982	$ 994
Write-offs, net of recoveries	$ 1	$ 1	$ 3	$ 3

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (19)	$ (18)	$ (34)	$ (31)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(11)	(14)	(22)	(25)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (8)	$ (4)	$ (12)	$ (6)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	6 Months Ended
	Jun. 30, 2021shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2021 (in shares)	249,868,415
Shareowner Direct Plan (in shares)	275,892
Equity-based compensation plans (in shares)	113,549
Shares outstanding, June 30, 2021 (in shares)	250,257,856

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 5,688
Beginning balance	$ 5,966	$ 5,702	5,888	$ 5,405
Net income attributable to common shareowners	144	134	315	304
Net income	146	136	320	309
Common stock dividends	(101)	(94)	(203)	(187)
Equity forward settlements and Shareowner Direct Plan issuances	7	7	15	235
Equity-based compensation plans and other	3	2	4	2
Adoption of new accounting standard, net of tax	(3,106)		(3,106)		$ (2,994)
Other comprehensive loss, net of tax		(3)		(2)
Ending balance	5,819		5,819
Ending balance	$ 6,019	$ 5,748	$ 6,019	$ 5,748
Common stock dividends (in dollars per share)	$ 0.4025	$ 0.38	$ 0.805	$ 0.76
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	2,712	2,674	2,704	2,446
Equity forward settlements and Shareowner Direct Plan issuances	7	7	14	235
Equity-based compensation plans and other	3	2	4	2
Ending balance	2,722	2,683	2,722	2,683
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,063	2,834	2,994	2,766
Net income attributable to common shareowners	144	134	315	304
Common stock dividends	(101)	(94)	(203)	(187)
Ending balance	3,106	2,874	3,106	2,874
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(1)	2	(1)	1
Other comprehensive loss, net of tax		(3)		(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)
Ending balance	(11)	(10)	(11)	(10)
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	3,942	3,595	3,964	3,472
Net income attributable to common shareowners	86	60	165	142
Net income	88	62	170	147
Common stock dividends	(99)	(59)	(200)	(118)
Adoption of new accounting standard, net of tax	(944)		(944)		(979)
Capital contributions from parent	50	75	50	175
Ending balance	3,779		3,779
Ending balance	3,979	3,671	3,979	3,671
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	2,752	2,448	2,752	2,348
Capital contributions from parent	50	75	50	175
Ending balance	2,802	2,523	2,802	2,523
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	957	914	979	891
Net income attributable to common shareowners	86	60	165	142
Common stock dividends	(99)	(59)	(200)	(118)
Ending balance	944	915	944	915
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	2,645	2,436	2,478	2,364
Net income	38	58	122	147
Common stock dividends	(43)	(42)	(85)	(84)
Adoption of new accounting standard, net of tax	(990)		(990)		$ (953)
Capital contributions from parent	85		210	25
Ending balance	2,725		2,725
Ending balance	2,725	2,452	2,725	2,452
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	1,584	1,459	1,459	1,434
Capital contributions from parent	85		210	25
Ending balance	1,669	1,459	1,669	1,459
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	995	911	953	864
Net income	38	58	122	147
Common stock dividends	(43)	(42)	(85)	(84)
Ending balance	$ 990	$ 927	$ 990	$ 927
Credit Losses ASU [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax						$ (9)

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Jun. 30, 2021USD ($)
Debt [Line Items]
Amount outstanding	$ 535
Weighted average interest rates	0.20%
Available credit facility capacity	$ 465
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 192
Weighted average interest rates	0.10%
Available credit facility capacity	$ 108

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 571	$ 271	$ 578	$ 463
Average amount outstanding (based on daily outstanding balances)	$ 452	$ 121	$ 438	$ 252
Weighted average interest rates	0.20%	0.50%	0.20%	1.50%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 19	$ 8	$ 19	$ 8
Average amount outstanding (based on daily outstanding balances)	$ 1	$ 0	$ 0	$ 0
Weighted average interest rates	0.20%	0.50%	0.20%	0.50%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 232	$ 182	$ 275	$ 212
Average amount outstanding (based on daily outstanding balances)	$ 177	$ 9	$ 183	$ 88
Weighted average interest rates	0.10%	0.50%	0.10%	1.70%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 817	$ 763	$ 1,718	$ 1,679
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	717	675	1,418	1,405
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	258	251	520	517
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	175	163	347	346
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	210	197	412	407
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	40	87	80
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	24	52	55
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69	59	239	211
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39	33	138	124
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	15	72	60
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2	8	6
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	9	21	21
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	23	22
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	9	18	19
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	5	3
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	19	38	41
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	19	38	41
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	455	432	944	951
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	402	388	788	813
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	142	136	281	283
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	115	109	225	229
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116	114	228	235
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	13	26	27
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	16	28	39
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	43	34	134	117
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	18	76	67
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	8	39	32
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2	5	4
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	6	14	14
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	22	21
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	9	18	19
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	4	2
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	341	312	736	687
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	315	287	630	592
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116	115	239	234
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	54	122	117
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	94	83	184	172
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32	27	61	53
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	8	24	16
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	25	105	94
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	15	62	57
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	7	33	28
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	3	2
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	3	7	7
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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effective Tax Rate [Line Items]
Overall income tax rate	(13.00%)	(6.00%)	(16.00%)	(10.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(13.00%)	(7.00%)	(15.00%)	(14.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(23.00%)	(9.00%)	(27.00%)	(9.00%)

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2021USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 322
Tax credits, carryforward amount	506
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	297
Tax credits, carryforward amount	302
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Tax credits, carryforward amount	182
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	652
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	29
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 10
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	$ 5
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 4
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	453,489

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 2	$ 6	$ 5
Interest cost	9	11	17	22
Expected return on plan assets	(17)	(17)	(34)	(35)
Amortization of actuarial loss	9	8	19	17
Settlement losses	0	0	0	4
Total	4	4	8	13
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	2
Interest cost	1	1	2	3
Expected return on plan assets	(1)	(1)	(2)	(3)
Amortization of actuarial loss	1	1	2	2
Settlement losses	0	0	0	0
Total	2	2	4	4
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	4	3
Interest cost	4	5	8	10
Expected return on plan assets	(8)	(8)	(16)	(16)
Amortization of actuarial loss	4	3	8	7
Total	2	2	4	4
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1	1
Interest cost	0	0	1	1
Expected return on plan assets	(1)	(1)	(2)	(2)
Amortization of actuarial loss	1	1	1	1
Total	1	1	1	1
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	2
Interest cost	4	4	8	9
Expected return on plan assets	(7)	(7)	(15)	(15)
Amortization of actuarial loss	4	4	9	8
Total	2	2	4	4
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0	1
Interest cost	1	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	0	1	1	1
Total	$ 1	$ 2	$ 2	$ 3

Benefit Plans (Recognized Compe

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

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	72,774
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 46.19
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	72,774
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.61
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	79,862
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.61

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 251
Revisions in estimated cash flows	32
Liabilities settled	(4)
Accretion expense	4
Balance, June 30	283
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	177
Revisions in estimated cash flows	26
Liabilities settled	(3)
Accretion expense	3
Balance, June 30	$ 203

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	6 Months Ended
	Jun. 30, 2021DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	16,242
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	4,936
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	11,306
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	179,960
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	94,049
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	85,911
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	5,148
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	1,946
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	3,202
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	4,284
Diesel Fuel (Gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	0
Diesel Fuel (Gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	4,284

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 77	$ 24
Non-current derivative assets	25	10
Current derivative liabilities	1	9
Non-current derivative liabilities	3	16
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	41	20
Non-current derivative assets	15	9
Current derivative liabilities	1	3
Non-current derivative liabilities	1	9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	36	4
Non-current derivative assets	10	1
Current derivative liabilities	0	6
Non-current derivative liabilities	$ 2	$ 7

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets:
Money market fund investments	$ 6	$ 44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	7,847	8,109
IPL [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	3,880	4,021
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,593	2,690
Commodity Contracts [Member]
Assets:
Derivatives	102	34
Liabilities:
Derivatives	4	25
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	56	29
Liabilities:
Derivatives	2	12
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	46	5
Liabilities:
Derivatives	2	13
Level 1 [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	7,846	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)	3,880	4,021
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,593	2,690
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	62	5
Liabilities:
Derivatives	3	25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	25	3
Liabilities:
Derivatives	1	12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	37	2
Liabilities:
Derivatives	2	13
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	1	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	154	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	40	29
Liabilities:
Derivatives	1	0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	31	26
Liabilities:
Derivatives	1	0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	6,776	6,777
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	3,346	3,345
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,131	2,130
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	102	34
Liabilities:
Derivatives	4	25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	56	29
Liabilities:
Derivatives	2	12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	46	5
Liabilities:
Derivatives	$ 2	$ 13

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 15	$ 14	$ 29	$ 21
Total net gains (losses) included in changes in net assets (realized/unrealized)	8	12	1	9
Purchases	21	14	21	14
Settlements	(5)	(4)	(12)	(8)
Ending balance	39	36	39	36
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30	8	12	1	9
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	14	13	26	18
Total net gains (losses) included in changes in net assets (realized/unrealized)	4	11	(2)	9
Purchases	16	11	16	11
Settlements	(4)	(3)	(10)	(6)
Ending balance	30	32	30	32
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30	4	11	(2)	9
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	107	188	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Settlements	47	6	(34)	6
Ending balance	154	194	154	194
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30	0	0	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	107	188	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Settlements	47	6	(34)	6
Ending balance	154	194	154	194
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 39	$ 15	$ 29	$ 36	$ 14	$ 21
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	13		18
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	26		11
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	30	$ 14	26	$ 32	$ 13	$ 18
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	13		17
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	17		9
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	0		1
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 9		$ 2

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,122
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	569
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	523
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	25
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	22
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	74
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum	$ 17
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent	6.00%
Obligations, maximum	$ 68
Credit loss liability	$ 5

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,122
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	569
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	523
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	909
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	456
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	453
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	89
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	48
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	41
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	124
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	65
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 29

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	6 Months Ended
	Jun. 30, 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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 817	$ 763	$ 1,718	$ 1,679
Operating income (loss)	176	168	374	356
Net income attributable to common shareowners	144	134	315	304
Net income	146	136	320	309
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	455	432	944	951
Operating income (loss)	111	88	214	185
Net income attributable to common shareowners	86	60	165	142
Net income	88	62	170	147
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	341	312	736	687
Operating income (loss)	55	72	145	166
Net income	38	58	122	147
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	717	675	1,418	1,405
Operating income (loss)	164	152	311	298
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	402	388	788	813
Operating income (loss)	107	82	179	149
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	315	287	630	592
Operating income (loss)	57	70	132	149
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	69	59	239	211
Operating income (loss)	3	7	47	49
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	43	34	134	117
Operating income (loss)	3	5	33	33
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	26	25	105	94
Operating income (loss)	0	2	14	16
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10	10	23	22
Operating income (loss)	(1)	1	1	4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10	10	22	21
Operating income (loss)	1	1	2	3
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	1	1
Operating income (loss)	(2)	0	(1)	1
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	796	744	1,680	1,638
Operating income (loss)	166	160	359	351
Net income attributable to common shareowners	124	118	287	289
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	21	19	38	41
Operating income (loss)	10	8	15	5
Net income attributable to common shareowners	$ 20	$ 16	$ 28	$ 15

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Jun. 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	$ 9	$ 9

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 48	$ 44	$ 88	$ 81
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	41	35	76	67
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	4	10	5	25
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	6	2	7	4
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	99	57	242	138
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 21	$ 20	$ 47	$ 40

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 126	$ 110
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 72	$ 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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 30	$ 25	$ 62	$ 53
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 6	$ 3	$ 9	$ 6