Alliant Energy (LNT) 10-Q 3 Nov 20 2020 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2020shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
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	249,760,663
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false
IPL [Member]
Entity Information [Line Items]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Incorporation, State or Country Code	IA
Entity Address, Address Line One	Alliant Energy Tower
Entity Address, City or Town	Cedar Rapids
Entity Address, State or Province	IA
Entity Address, Postal Zip Code	52401
City Area Code	319
Local Phone Number	786-4411
Entity File Number	1-4117
Entity Tax Identification Number	42-0331370
Title of 12(b) Security	5.100% Series D Cumulative Perpetual Preferred Stock, $0.01 Par Value
Trading Symbol	IPLDP
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Information [Line Items]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	0-337
Entity Tax Identification Number	39-0714890
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Electric utility	$ 852	$ 916	$ 2,257	$ 2,350
Gas utility	42	42	253	323
Other utility	10	11	32	33
Non-utility	16	21	57	62
Total revenues	920	990	2,599	2,768
Operating expenses:
Electric production fuel and purchased power	179	219	527	602
Electric transmission service	132	127	326	363
Cost of gas sold	11	9	117	151
Other operation and maintenance	143	174	465	527
Depreciation and amortization	156	144	454	424
Taxes other than income taxes	27	27	82	84
Total operating expenses	648	700	1,971	2,151
Operating income	272	290	628	617
Other (income) and deductions:
Interest expense	68	68	207	204
Equity income from unconsolidated investments, net	(15)	(12)	(46)	(35)
Allowance for funds used during construction	(13)	(22)	(51)	(66)
Other	3	4	7	11
Total other (income) and deductions	43	38	117	114
Income before income taxes	229	252	511	503
Income tax expense (benefit)	(20)	23	(47)	49
Net income	249	229	558	454
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	$ 246	$ 226	$ 550	$ 446
Weighted average number of common shares outstanding:
Basic (in shares)	249.7	239.1	247.9	237.7
Diluted (in shares)	250	239.9	248.1	238.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.99	$ 0.95	$ 2.22	$ 1.88
Diluted (in dollars per share)	$ 0.98	$ 0.94	$ 2.22	$ 1.87
IPL [Member]
Revenues:
Electric utility	$ 519	$ 561	$ 1,332	$ 1,373
Gas utility	24	25	141	188
Other utility	10	11	31	32
Total revenues	553	597	1,504	1,593
Operating expenses:
Electric production fuel and purchased power	102	127	304	339
Electric transmission service	93	92	212	257
Cost of gas sold	6	6	63	80
Other operation and maintenance	85	100	269	306
Depreciation and amortization	89	84	264	243
Taxes other than income taxes	16	14	45	46
Total operating expenses	391	423	1,157	1,271
Operating income	162	174	347	322
Other (income) and deductions:
Interest expense	35	32	104	93
Allowance for funds used during construction	(6)	(11)	(21)	(34)
Other	1	2	3	5
Total other (income) and deductions	30	23	86	64
Income before income taxes	132	151	261	258
Income tax expense (benefit)	(19)	7	(37)	11
Net income	151	144	298	247
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	148	141	290	239
WPL [Member]
Revenues:
Electric utility	333	355	925	977
Gas utility	18	17	112	135
Other utility	0	0	1	1
Total revenues	351	372	1,038	1,113
Operating expenses:
Electric production fuel and purchased power	78	92	223	263
Electric transmission service	39	36	114	106
Cost of gas sold	4	3	53	71
Other operation and maintenance	65	62	172	188
Depreciation and amortization	65	59	186	177
Taxes other than income taxes	11	12	35	35
Total operating expenses	262	264	783	840
Operating income	89	108	255	273
Other (income) and deductions:
Interest expense	26	25	78	77
Allowance for funds used during construction	(6)	(11)	(29)	(31)
Other	1	1	3	4
Total other (income) and deductions	21	15	52	50
Income before income taxes	68	93	203	223
Income tax expense (benefit)	(5)	17	(17)	40
Net income	$ 73	$ 76	$ 220	$ 183

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 189	$ 16
Accounts receivable, less allowance for expected credit losses	399	402
Production fuel, at weighted average cost	62	78
Gas stored underground, at weighted average cost	48	49
Materials and supplies, at weighted average cost	113	100
Regulatory assets	74	87
Prepaid gross receipts tax	30	42
Other	118	102
Total current assets	1,033	876
Property, plant and equipment, net	14,199	13,527
Investments:
ATC Holdings	328	320
Other	150	148
Total investments	478	468
Other assets:
Regulatory assets	1,762	1,758
Deferred charges and other	68	72
Total other assets	1,830	1,830
Total assets	17,540	16,701
Current liabilities:
Current maturities of long-term debt	7	657
Commercial paper	422	337
Accounts payable	417	422
Regulatory liabilities	163	212
Other	286	426
Total current liabilities	1,295	2,054
Long-term debt, net (excluding current portion)	6,574	5,533
Other liabilities:
Deferred tax liabilities	1,803	1,714
Regulatory liabilities	1,188	1,212
Pension and other benefit obligations	423	484
Other	348	299
Total other liabilities	3,762	3,709
Commitments and contingencies (Note 13)
Common equity:
Common stock	2	2
Additional paid-in capital	2,693	2,446
Retained earnings	3,026	2,766
Accumulated other comprehensive income (loss)	(1)	1
Shares in deferred compensation trust - 374,246 and 381,232 shares at a weighted average cost of $28.28 and $26.24 per share	(11)	(10)
Total common equity	5,709	5,205
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	5,909	5,405
Total liabilities and equity	17,540	16,701
IPL [Member]
Current assets:
Cash and cash equivalents	185	9
Accounts receivable, less allowance for expected credit losses	219	203
Production fuel, at weighted average cost	45	47
Gas stored underground, at weighted average cost	21	22
Materials and supplies, at weighted average cost	63	55
Regulatory assets	52	44
Other	53	29
Total current assets	638	409
Property, plant and equipment, net	7,818	7,481
Other assets:
Regulatory assets	1,366	1,356
Deferred charges and other	36	31
Total other assets	1,402	1,387
Total assets	9,858	9,277
Current liabilities:
Current maturities of long-term debt	0	200
Accounts payable	231	207
Regulatory liabilities	117	116
Other	198	307
Total current liabilities	546	830
Long-term debt, net (excluding current portion)	3,344	2,947
Other liabilities:
Deferred tax liabilities	1,028	1,008
Regulatory liabilities	574	599
Pension and other benefit obligations	149	168
Other	287	253
Total other liabilities	2,038	2,028
Commitments and contingencies (Note 13)
Common equity:
Common stock	33	33
Additional paid-in capital	2,693	2,348
Retained earnings	1,004	891
Total common equity	3,730	3,272
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,930	3,472
Total liabilities and equity	9,858	9,277
WPL [Member]
Current assets:
Cash and cash equivalents	2	4
Accounts receivable, less allowance for expected credit losses	170	191
Production fuel, at weighted average cost	17	31
Gas stored underground, at weighted average cost	27	27
Materials and supplies, at weighted average cost	48	43
Regulatory assets	22	43
Prepaid gross receipts tax	30	42
Other	22	62
Total current assets	338	443
Property, plant and equipment, net	5,977	5,638
Other assets:
Regulatory assets	396	402
Deferred charges and other	33	24
Total other assets	429	426
Total assets	6,744	6,507
Current liabilities:
Current maturities of long-term debt	0	150
Commercial paper	139	168
Accounts payable	126	160
Regulatory liabilities	46	96
Other	117	116
Total current liabilities	428	690
Long-term debt, net (excluding current portion)	2,130	1,783
Other liabilities:
Deferred tax liabilities	696	626
Regulatory liabilities	614	613
Finance lease obligations - Sheboygan Falls Energy Facility	44	51
Pension and other benefit obligations	189	211
Other	161	169
Total other liabilities	1,704	1,670
Commitments and contingencies (Note 13)
Common equity:
Common stock	66	66
Additional paid-in capital	1,459	1,434
Retained earnings	957	864
Total common equity	2,482	2,364
Total equity	2,482	2,364
Total liabilities and equity	$ 6,744	$ 6,507

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
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)	249,760,663	245,022,800
Shares in deferred compensation trust (in shares)	374,246	381,232
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 28.28	$ 26.24
IPL [Member]
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed Consolidated Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 558	$ 454
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	454	424
Deferred tax expense (benefit) and tax credits	(48)	53
Equity component of allowance for funds used during construction	(36)	(46)
Other	19	17
Other changes in assets and liabilities:
Accounts receivable	(316)	(359)
Regulatory liabilities	(72)	(12)
Deferred income taxes	143	45
Pension and other benefit obligations	(61)	(33)
DAEC PPA amendment buyout payment	(110)	0
Other	(95)	(34)
Net cash flows from operating activities	436	509
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(935)	(1,004)
Other construction and acquisition expenditures	(39)	(71)
Cash receipts on sold receivables	318	256
Other	(23)	(42)
Net cash flows used for investing activities	(679)	(861)
Cash flows from (used for) financing activities:
Common stock dividends	(281)	(253)
Proceeds from issuance of common stock, net	241	185
Proceeds from issuance of long-term debt	1,050	950
Payments to retire long-term debt	(654)	(253)
Net change in commercial paper	85	(92)
Other	(22)	(11)
Net cash flows from (used for) financing activities	419	526
Net increase (decrease) in cash, cash equivalents and restricted cash	176	174
Cash, cash equivalents and restricted cash at beginning of period	18	26
Cash, cash equivalents and restricted cash at end of period	194	200
Supplemental cash flows information:
Interest	(197)	(195)
Income taxes, net	6	1
Significant non-cash investing and financing activities:
Accrued capital expenditures	202	254
Beneficial interest obtained in exchange for securitized accounts receivable	201	237
IPL [Member]
Cash flows from operating activities:
Net income	298	247
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	264	243
Deferred tax expense (benefit) and tax credits	(42)	(14)
Equity component of allowance for funds used during construction	(15)	(25)
Other	6	2
Other changes in assets and liabilities:
Accounts receivable	(337)	(365)
Regulatory assets	(32)	(13)
Deferred income taxes	62	32
Pension and other benefit obligations	(19)	(13)
DAEC PPA amendment buyout payment	(110)	0
Other	(56)	45
Net cash flows from operating activities	19	139
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(465)	(696)
Cash receipts on sold receivables	318	256
Other	(55)	(44)
Net cash flows used for investing activities	(202)	(484)
Cash flows from (used for) financing activities:
Common stock dividends	(177)	(126)
Capital contributions from parent	345	100
Proceeds from issuance of long-term debt	400	600
Payments to retire long-term debt	(200)	0
Net change in commercial paper	0	(50)
Other	(9)	(6)
Net cash flows from (used for) financing activities	359	518
Net increase (decrease) in cash, cash equivalents and restricted cash	176	173
Cash, cash equivalents and restricted cash at beginning of period	9	12
Cash, cash equivalents and restricted cash at end of period	185	185
Supplemental cash flows information:
Interest	(109)	(94)
Income taxes, net	(12)	8
Significant non-cash investing and financing activities:
Accrued capital expenditures	150	180
Beneficial interest obtained in exchange for securitized accounts receivable	201	237
WPL [Member]
Cash flows from operating activities:
Net income	220	183
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	186	177
Deferred tax expense (benefit) and tax credits	(9)	55
Other	(8)	(8)
Other changes in assets and liabilities:
Regulatory liabilities	(61)	(29)
Deferred income taxes	79	16
Other	(5)	(34)
Net cash flows from operating activities	402	360
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(470)	(308)
Other	5	(27)
Net cash flows used for investing activities	(465)	(335)
Cash flows from (used for) financing activities:
Common stock dividends	(127)	(108)
Capital contributions from parent	25	100
Proceeds from issuance of long-term debt	350	350
Payments to retire long-term debt	(150)	(250)
Net change in commercial paper	(29)	(105)
Other	(8)	(11)
Net cash flows from (used for) financing activities	61	(24)
Net increase (decrease) in cash, cash equivalents and restricted cash	(2)	1
Cash, cash equivalents and restricted cash at beginning of period	4	9
Cash, cash equivalents and restricted cash at end of period	2	10
Supplemental cash flows information:
Interest	(71)	(74)
Income taxes, net	5	(7)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 50	$ 70

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes . NOTE 1(b) Cash and Cash Equivalents - At September 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $183 million and $183 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes . NOTE 1(b) Cash and Cash Equivalents - At September 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $183 million and $183 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes . NOTE 1(b) Cash and Cash Equivalents - At September 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $183 million and $183 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the nine months ended September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. IPL’s DAEC PPA amendment - In September 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The payment was recorded as a reduction to “Other current liabilities” on Alliant Energy’s and IPL’s balance sheets and was included in “ DAEC PPA amendment buyout payment” in Alliant Energy’s and IPL’s cash flows used for operating activities for the nine months ended September 30, 2020. The buyout payment will be recovered from IPL’s retail and wholesale customers beginning in the fourth quarter of 2020 through the end of 2025. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in 2020 related to MISO transmission owner return on equity complaints. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in the third quarter of 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. The liquidated damages are expected to be returned to WPL’s customers as determined in future regulatory proceedings. August 2020 Derecho Windstorm - In August 2020, a derecho windstorm caused considerable damage to IPL’s electric distribution system in its service territory, and over 250,000 of its customers lost power. IPL completed its initial restoration and rebuilding efforts in August 2020 and expects permanent repairs to the system to continue throughout 2020. IPL’s current estimate of the total cost of the windstorm is approximately $140 million , and as of September 30, 2020, approximately $130 million was recorded substantially to “Property, plant and equipment, net” on Alliant Energy’s and IPL’s balance sheets . Tax benefits and the incremental operation and maintenance expenses resulting from the windstorm were deferred and recorded as a net regulatory liability of $7 million as of September 30, 2020, which is included in “Other” regulatory liabilities in the above table. In November 2020, IPL filed a request with the IUB for utilization of a regulatory account to track certain incremental costs and benefits incurred resulting from the windstorm until IPL’s next rate proceeding.
IPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the nine months ended September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. IPL’s DAEC PPA amendment - In September 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The payment was recorded as a reduction to “Other current liabilities” on Alliant Energy’s and IPL’s balance sheets and was included in “ DAEC PPA amendment buyout payment” in Alliant Energy’s and IPL’s cash flows used for operating activities for the nine months ended September 30, 2020. The buyout payment will be recovered from IPL’s retail and wholesale customers beginning in the fourth quarter of 2020 through the end of 2025. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in 2020 related to MISO transmission owner return on equity complaints. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in the third quarter of 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. The liquidated damages are expected to be returned to WPL’s customers as determined in future regulatory proceedings. August 2020 Derecho Windstorm - In August 2020, a derecho windstorm caused considerable damage to IPL’s electric distribution system in its service territory, and over 250,000 of its customers lost power. IPL completed its initial restoration and rebuilding efforts in August 2020 and expects permanent repairs to the system to continue throughout 2020. IPL’s current estimate of the total cost of the windstorm is approximately $140 million , and as of September 30, 2020, approximately $130 million was recorded substantially to “Property, plant and equipment, net” on Alliant Energy’s and IPL’s balance sheets . Tax benefits and the incremental operation and maintenance expenses resulting from the windstorm were deferred and recorded as a net regulatory liability of $7 million as of September 30, 2020, which is included in “Other” regulatory liabilities in the above table. In November 2020, IPL filed a request with the IUB for utilization of a regulatory account to track certain incremental costs and benefits incurred resulting from the windstorm until IPL’s next rate proceeding.
WPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the nine months ended September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. IPL’s DAEC PPA amendment - In September 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The payment was recorded as a reduction to “Other current liabilities” on Alliant Energy’s and IPL’s balance sheets and was included in “ DAEC PPA amendment buyout payment” in Alliant Energy’s and IPL’s cash flows used for operating activities for the nine months ended September 30, 2020. The buyout payment will be recovered from IPL’s retail and wholesale customers beginning in the fourth quarter of 2020 through the end of 2025. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in 2020 related to MISO transmission owner return on equity complaints. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in the third quarter of 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. The liquidated damages are expected to be returned to WPL’s customers as determined in future regulatory proceedings. August 2020 Derecho Windstorm - In August 2020, a derecho windstorm caused considerable damage to IPL’s electric distribution system in its service territory, and over 250,000 of its customers lost power. IPL completed its initial restoration and rebuilding efforts in August 2020 and expects permanent repairs to the system to continue throughout 2020. IPL’s current estimate of the total cost of the windstorm is approximately $140 million , and as of September 30, 2020, approximately $130 million was recorded substantially to “Property, plant and equipment, net” on Alliant Energy’s and IPL’s balance sheets . Tax benefits and the incremental operation and maintenance expenses resulting from the windstorm were deferred and recorded as a net regulatory liability of $7 million as of September 30, 2020, which is included in “Other” regulatory liabilities in the above table. In November 2020, IPL filed a request with the IUB for utilization of a regulatory account to track certain incremental costs and benefits incurred resulting from the windstorm until IPL’s next rate proceeding.

Receivables

Receivables	9 Months Ended
	Sep. 30, 2020
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191 Note 3(b) Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of September 30, 2020 , IPL had $109 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $1 $103 $96 $108 Average outstanding aggregate cash proceeds 1 45 12 43 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2020 December 31, 2019 Customer accounts receivable $148 $125 Unbilled utility revenues 67 95 Other receivables — 1 Receivables sold to third party 215 221 Less: cash proceeds 1 27 Deferred proceeds 214 194 Less: allowance for expected credit losses 13 6 Fair value of deferred proceeds $201 $188 As of September 30, 2020 , outstanding receivables past due under the Receivables Agreement were $27 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Collections $561 $592 $1,555 $1,636 Write-offs, net of recoveries 1 3 4 11
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191 Note 3(b) Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of September 30, 2020 , IPL had $109 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $1 $103 $96 $108 Average outstanding aggregate cash proceeds 1 45 12 43 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2020 December 31, 2019 Customer accounts receivable $148 $125 Unbilled utility revenues 67 95 Other receivables — 1 Receivables sold to third party 215 221 Less: cash proceeds 1 27 Deferred proceeds 214 194 Less: allowance for expected credit losses 13 6 Fair value of deferred proceeds $201 $188 As of September 30, 2020 , outstanding receivables past due under the Receivables Agreement were $27 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Collections $561 $592 $1,555 $1,636 Write-offs, net of recoveries 1 3 4 11
WPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191

Investments

Investments	9 Months Ended
	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC Holdings ($11 ) ($11 ) ($36 ) ($30 ) Non-utility wind farm in Oklahoma (2 ) — (6 ) (3 ) Other (2 ) (1 ) (4 ) (2 ) ($15 ) ($12 ) ($46 ) ($35 )

Common Equity

Common Equity	9 Months Ended
	Sep. 30, 2020
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 364,531 Equity-based compensation plans 98,205 Shares outstanding, September 30, 2020 249,760,663 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 364,531 Equity-based compensation plans 98,205 Shares outstanding, September 30, 2020 249,760,663 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 364,531 Equity-based compensation plans 98,205 Shares outstanding, September 30, 2020 249,760,663 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt [Line Items]
Debt	DEBT NOTE 6(a) 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): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of September 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) 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): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of September 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) 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): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of September 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.

Revenues

Revenues	9 Months Ended
	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2 As of September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million , $4 million and $3 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2 As of September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million , $4 million and $3 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2 As of September 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7 million , $4 million and $3 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2020
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196 $134 Revisions in estimated cash flows 1 — Liabilities settled (7 ) (5 ) Liabilities incurred (a) 38 38 Accretion expense 5 4 Balance, September 30 $233 $171 (a) During the nine months ended September 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North, Golden Plains and Richland wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196 $134 Revisions in estimated cash flows 1 — Liabilities settled (7 ) (5 ) Liabilities incurred (a) 38 38 Accretion expense 5 4 Balance, September 30 $233 $171 (a) During the nine months ended September 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North, Golden Plains and Richland wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2020
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10 Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2020 and December 31, 2019 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10 Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2020 and December 31, 2019 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10 Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2020 and December 31, 2019 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $36 $13 $194 $215 Total net gains included in changes in net assets (realized/unrealized) — 13 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (5 ) (3 ) 7 22 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $13 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $21 $12 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 8 7 — — Transfers out of Level 3 — 3 — — Purchases 14 14 — — Sales (1 ) — — — Settlements (a) (12 ) (14 ) 13 118 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $8 $10 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $32 $9 $194 $215 Total net gains (losses) included in changes in net assets (realized/unrealized) (1 ) 12 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (4 ) (2 ) 7 22 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $18 $9 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 7 9 — — Transfers out of Level 3 — 2 — — Purchases 11 9 — — Sales (1 ) — — — Settlements (a) (9 ) (11 ) 13 118 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $7 $10 $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $36 $13 $194 $215 Total net gains included in changes in net assets (realized/unrealized) — 13 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (5 ) (3 ) 7 22 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $13 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $21 $12 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 8 7 — — Transfers out of Level 3 — 3 — — Purchases 14 14 — — Sales (1 ) — — — Settlements (a) (12 ) (14 ) 13 118 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $8 $10 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $32 $9 $194 $215 Total net gains (losses) included in changes in net assets (realized/unrealized) (1 ) 12 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (4 ) (2 ) 7 22 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $18 $9 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 7 9 — — Transfers out of Level 3 — 2 — — Purchases 11 9 — — Sales (1 ) — — — Settlements (a) (9 ) (11 ) 13 118 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $7 $10 $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $36 $13 $194 $215 Total net gains included in changes in net assets (realized/unrealized) — 13 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (5 ) (3 ) 7 22 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $13 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $21 $12 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 8 7 — — Transfers out of Level 3 — 3 — — Purchases 14 14 — — Sales (1 ) — — — Settlements (a) (12 ) (14 ) 13 118 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $8 $10 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $32 $9 $194 $215 Total net gains (losses) included in changes in net assets (realized/unrealized) (1 ) 12 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (4 ) (2 ) 7 22 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $18 $9 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 7 9 — — Transfers out of Level 3 — 2 — — Purchases 11 9 — — Sales (1 ) — — — Settlements (a) (9 ) (11 ) 13 118 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $7 $10 $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2020
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. WPL’s projects include the expansion of solar and wind generation and its gas distribution system in Western Wisconsin. At September 30, 2020 , Alliant Energy’s and WPL’s minimum future commitments for these projects were $21 million and $18 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 September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 . Refer to Note 2 for discussion of an amendment to shorten the term of the DAEC PPA, which resulted in IPL making a buyout payment in September 2020. 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 September 30, 2020 , 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, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. Whiting Petroleum’s creditworthiness deteriorated in the first quarter of 2020, likely from significantly depressed oil and gas prices and general market conditions, and as a result, the credit loss liability was increased to $20 million in the first quarter of 2020. In April 2020, Whiting Petroleum filed for bankruptcy, and in September 2020, Whiting Petroleum completed its reorganization and emerged from bankruptcy. As a result of Whiting Petroleum’s completed bankruptcy proceedings, as well as additional information regarding the guarantees obtained from the bankruptcy proceedings, the credit loss liability was decreased to $5 million in the third quarter of 2020. The credit loss liability is recorded in “Other liabilities” on Alliant Energy’s balance sheet as of September 30, 2020 . For the three and nine months ended September 30, 2020 , the pre-tax credit loss adjustments of $15 million and $7 million , respectively, were recorded as reductions in Alliant Energy’s “Other operation and maintenance” expenses. 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 September 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expired in October 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 September 30, 2020 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At September 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $9 - $24 Current and non-current environmental liabilities 16 13 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 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. NOTE 13(e) Collective Bargaining Agreements - In August 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired and a new agreement was reached, which expires August 31, 2024. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. For the nine months ended September 30, 2020, IPL and WPL received $15 million and $5 million , respectively, in refunds related to the FERC orders. In October 2020, FERC extended the time to complete additional refunds to September 2021. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.
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. WPL’s projects include the expansion of solar and wind generation and its gas distribution system in Western Wisconsin. At September 30, 2020 , Alliant Energy’s and WPL’s minimum future commitments for these projects were $21 million and $18 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 September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 . Refer to Note 2 for discussion of an amendment to shorten the term of the DAEC PPA, which resulted in IPL making a buyout payment in September 2020. 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 September 30, 2020 , 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, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. Whiting Petroleum’s creditworthiness deteriorated in the first quarter of 2020, likely from significantly depressed oil and gas prices and general market conditions, and as a result, the credit loss liability was increased to $20 million in the first quarter of 2020. In April 2020, Whiting Petroleum filed for bankruptcy, and in September 2020, Whiting Petroleum completed its reorganization and emerged from bankruptcy. As a result of Whiting Petroleum’s completed bankruptcy proceedings, as well as additional information regarding the guarantees obtained from the bankruptcy proceedings, the credit loss liability was decreased to $5 million in the third quarter of 2020. The credit loss liability is recorded in “Other liabilities” on Alliant Energy’s balance sheet as of September 30, 2020 . For the three and nine months ended September 30, 2020 , the pre-tax credit loss adjustments of $15 million and $7 million , respectively, were recorded as reductions in Alliant Energy’s “Other operation and maintenance” expenses. 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 September 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expired in October 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 September 30, 2020 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At September 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $9 - $24 Current and non-current environmental liabilities 16 13 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 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. NOTE 13(e) Collective Bargaining Agreements - In August 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired and a new agreement was reached, which expires August 31, 2024. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. For the nine months ended September 30, 2020, IPL and WPL received $15 million and $5 million , respectively, in refunds related to the FERC orders. In October 2020, FERC extended the time to complete additional refunds to September 2021. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.
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. WPL’s projects include the expansion of solar and wind generation and its gas distribution system in Western Wisconsin. At September 30, 2020 , Alliant Energy’s and WPL’s minimum future commitments for these projects were $21 million and $18 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 September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 . Refer to Note 2 for discussion of an amendment to shorten the term of the DAEC PPA, which resulted in IPL making a buyout payment in September 2020. 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 September 30, 2020 , 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, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. Whiting Petroleum’s creditworthiness deteriorated in the first quarter of 2020, likely from significantly depressed oil and gas prices and general market conditions, and as a result, the credit loss liability was increased to $20 million in the first quarter of 2020. In April 2020, Whiting Petroleum filed for bankruptcy, and in September 2020, Whiting Petroleum completed its reorganization and emerged from bankruptcy. As a result of Whiting Petroleum’s completed bankruptcy proceedings, as well as additional information regarding the guarantees obtained from the bankruptcy proceedings, the credit loss liability was decreased to $5 million in the third quarter of 2020. The credit loss liability is recorded in “Other liabilities” on Alliant Energy’s balance sheet as of September 30, 2020 . For the three and nine months ended September 30, 2020 , the pre-tax credit loss adjustments of $15 million and $7 million , respectively, were recorded as reductions in Alliant Energy’s “Other operation and maintenance” expenses. 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 September 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expired in October 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 September 30, 2020 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At September 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $9 - $24 Current and non-current environmental liabilities 16 13 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 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. NOTE 13(e) Collective Bargaining Agreements - In August 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired and a new agreement was reached, which expires August 31, 2024. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. For the nine months ended September 30, 2020, IPL and WPL received $15 million and $5 million , respectively, in refunds related to the FERC orders. In October 2020, FERC extended the time to complete additional refunds to September 2021. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.

Segments Of Business

Segments Of Business	9 Months Ended
	Sep. 30, 2020
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC billings to WPL $27 $28 $80 $82 WPL billings to ATC 2 3 8 10 WPL owed ATC net amounts of $9 million as of September 30, 2020 and $9 million as of December 31, 2019 . In the second quarter of 2020, WPL received $46 million from ATC related to construction deposits WPL previously provided ATC for transmission network upgrades for West Riverside, which is substantially recorded in “Other” in Alliant Energy’s and WPL’s cash flows from investing activities.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC billings to WPL $27 $28 $80 $82 WPL billings to ATC 2 3 8 10 WPL owed ATC net amounts of $9 million as of September 30, 2020 and $9 million as of December 31, 2019 . In the second quarter of 2020, WPL received $46 million from ATC related to construction deposits WPL previously provided ATC for transmission network upgrades for West Riverside, which is substantially recorded in “Other” in Alliant Energy’s and WPL’s cash flows from investing activities.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2020
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes .
Cash and Cash Equivalents	At September 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $183 million and $183 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively.
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes .
Cash and Cash Equivalents	At September 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $183 million and $183 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively.
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions, closures of commercial spaces and industrial facilities, and more people working from home in Alliant Energy’s service territories. For the three and nine months ended September 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
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 .
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19, the derecho windstorm and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $9 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the nine months ended September 30, 2020 .

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2020
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $877 $818 $829 $777 $48 $41 Pension and OPEB costs 492 524 247 263 245 261 Assets retired early 118 134 79 88 39 46 Asset retirement obligations 115 112 79 76 36 36 IPL’s DAEC PPA amendment 110 108 110 108 — — Derivatives 20 39 8 18 12 21 Emission allowances 19 21 19 21 — — Other 85 89 47 49 38 40 $1,836 $1,845 $1,418 $1,400 $418 $445
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $746 $836 $334 $351 $412 $485 Cost of removal obligations 371 388 241 257 130 131 Electric transmission cost recovery 62 88 30 51 32 37 Derivatives 40 20 27 17 13 3 WPL’s West Riverside liquidated damages 36 — — — 36 — Commodity cost recovery 22 24 19 9 3 15 WPL’s earnings sharing mechanism 22 22 — — 22 22 Other 52 46 40 30 12 16 $1,351 $1,424 $691 $715 $660 $709

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 2020
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $1 $103 $96 $108 Average outstanding aggregate cash proceeds 1 45 12 43
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2020 December 31, 2019 Customer accounts receivable $148 $125 Unbilled utility revenues 67 95 Other receivables — 1 Receivables sold to third party 215 221 Less: cash proceeds 1 27 Deferred proceeds 214 194 Less: allowance for expected credit losses 13 6 Fair value of deferred proceeds $201 $188
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Collections $561 $592 $1,555 $1,636 Write-offs, net of recoveries 1 3 4 11
IPL [Member]
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $1 $103 $96 $108 Average outstanding aggregate cash proceeds 1 45 12 43
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2020 December 31, 2019 Customer accounts receivable $148 $125 Unbilled utility revenues 67 95 Other receivables — 1 Receivables sold to third party 215 221 Less: cash proceeds 1 27 Deferred proceeds 214 194 Less: allowance for expected credit losses 13 6 Fair value of deferred proceeds $201 $188
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 Collections $561 $592 $1,555 $1,636 Write-offs, net of recoveries 1 3 4 11
WPL [Member]
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Customer $95 $92 $— $— $86 $84 Unbilled utility revenues 62 82 — — 62 82 Deferred proceeds 201 188 201 188 — — Other 54 47 20 16 33 31 Allowance for expected credit losses (13 ) (7 ) (2 ) (1 ) (11 ) (6 ) $399 $402 $219 $203 $170 $191

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC Holdings ($11 ) ($11 ) ($36 ) ($30 ) Non-utility wind farm in Oklahoma (2 ) — (6 ) (3 ) Other (2 ) (1 ) (4 ) (2 ) ($15 ) ($12 ) ($46 ) ($35 )

Common Equity (Tables)

Common Equity (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 364,531 Equity-based compensation plans 98,205 Shares outstanding, September 30, 2020 249,760,663
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325
IPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325
WPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $2 $2,683 $2,874 ($1 ) ($10 ) $200 $5,748 Net income attributable to Alliant Energy common shareowners 246 246 Common stock dividends ($0.38 per share) (94 ) (94 ) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1 ) 3 Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $2 $2,109 $2,598 $1 ($10 ) $200 $4,900 Net income attributable to Alliant Energy common shareowners 226 226 Common stock dividends ($0.355 per share) (85 ) (85 ) Equity forward settlements and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 3 Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $2 $2,446 $2,766 $1 ($10 ) $200 $5,405 Net income attributable to Alliant Energy common shareowners 550 550 Common stock dividends ($1.14 per share) (281 ) (281 ) Equity forward settlements and Shareowner Direct Plan issuances 241 241 Equity-based compensation plans and other 6 (1 ) 5 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (9 ) (9 ) Other comprehensive loss, net of tax (2 ) (2 ) Ending balance, September 30, 2020 $2 $2,693 $3,026 ($1 ) ($11 ) $200 $5,909 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $2 $2,046 $2,546 $2 ($10 ) $200 $4,786 Net income attributable to Alliant Energy common shareowners 446 446 Common stock dividends ($1.065 per share) (253 ) (253 ) Equity forward settlements and Shareowner Direct Plan issuances 185 185 Equity-based compensation plans and other 6 6 Other comprehensive loss, net of tax (1 ) (1 ) Ending balance, September 30, 2019 $2 $2,237 $2,739 $1 ($10 ) $200 $5,169 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $33 $2,523 $915 $200 $3,671 Net income available for common stock 148 148 Common stock dividends (59 ) (59 ) Capital contributions from parent 170 170 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $33 $2,323 $789 $200 $3,345 Net income available for common stock 141 141 Common stock dividends (42 ) (42 ) Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $33 $2,348 $891 $200 $3,472 Net income available for common stock 290 290 Common stock dividends (177 ) (177 ) Capital contributions from parent 345 345 Ending balance, September 30, 2020 $33 $2,693 $1,004 $200 $3,930 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $33 $2,223 $775 $200 $3,231 Net income available for common stock 239 239 Common stock dividends (126 ) (126 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $33 $2,323 $888 $200 $3,444 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2020 Beginning balance, June 30, 2020 $66 $1,459 $927 $2,452 Net income 73 73 Common stock dividends (43 ) (43 ) Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Three Months Ended September 30, 2019 Beginning balance, June 30, 2019 $66 $1,309 $810 $2,185 Net income 76 76 Common stock dividends (36 ) (36 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2020 Beginning balance, December 31, 2019 $66 $1,434 $864 $2,364 Net income 220 220 Common stock dividends (127 ) (127 ) Capital contributions from parent 25 25 Ending balance, September 30, 2020 $66 $1,459 $957 $2,482 Nine Months Ended September 30, 2019 Beginning balance, December 31, 2018 $66 $1,309 $775 $2,150 Net income 183 183 Common stock dividends (108 ) (108 ) Capital contributions from parent 100 100 Ending balance, September 30, 2019 $66 $1,409 $850 $2,325

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): September 30, 2020 Alliant Energy IPL WPL Amount outstanding $422 $— $139 Weighted average interest rates 0.2% N/A 0.1% Available credit facility capacity $578 $250 $161 Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $422 $472 $— $— $139 $90 Average amount outstanding (based on daily outstanding balances) $252 $400 $— $— $83 $27 Weighted average interest rates 0.2% 2.5% N/A N/A 0.2% 2.3% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $463 $601 $8 $50 $212 $195 Average amount outstanding (based on daily outstanding balances) $252 $476 $— $— $86 $102 Weighted average interest rates 1.1% 2.6% 0.5% 2.8% 1.2% 2.5%

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $328 $332 $189 $196 $139 $136 Retail - commercial 210 231 142 158 68 73 Retail - industrial 241 264 149 158 92 106 Wholesale 47 50 17 18 30 32 Bulk power and other 26 39 22 31 4 8 Total Electric Utility 852 916 519 561 333 355 Gas Utility: Retail - residential 22 20 12 12 10 8 Retail - commercial 10 10 6 6 4 4 Retail - industrial 2 3 1 2 1 1 Transportation/other 8 9 5 5 3 4 Total Gas Utility 42 42 24 25 18 17 Other Utility: Steam 8 9 8 9 — — Other utility 2 2 2 2 — — Total Other Utility 10 11 10 11 — — Non-Utility and Other: Transportation and other 16 21 — — — — Total Non-Utility and Other 16 21 — — — — Total revenues $920 $990 $553 $597 $351 $372 Alliant Energy IPL WPL Nine Months Ended September 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $845 $840 $472 $470 $373 $370 Retail - commercial 556 583 371 386 185 197 Retail - industrial 648 686 384 392 264 294 Wholesale 127 137 44 49 83 88 Bulk power and other 81 104 61 76 20 28 Total Electric Utility 2,257 2,350 1,332 1,373 925 977 Gas Utility: Retail - residential 146 187 79 109 67 78 Retail - commercial 70 90 38 50 32 40 Retail - industrial 8 10 5 7 3 3 Transportation/other 29 36 19 22 10 14 Total Gas Utility 253 323 141 188 112 135 Other Utility: Steam 27 27 27 27 — — Other utility 5 6 4 5 1 1 Total Other Utility 32 33 31 32 1 1 Non-Utility and Other: Transportation and other 57 62 — — — — Total Non-Utility and Other 57 62 — — — — Total revenues $2,599 $2,768 $1,504 $1,593 $1,038 $1,113

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2020
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18%
Summary Of Tax Credit Carryforwards	At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18%
Summary Of Tax Credit Carryforwards	At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173
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 overall effective income tax rates for the three and nine months ended September 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (9%) 9% (9%) 10% (14%) 5% (14%) 4% (7%) 18% (8%) 18%
Summary Of Tax Credit Carryforwards	At September 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $371 $343 $3 State net operating losses 2020-2040 623 10 2 Federal tax credits 2022-2040 446 252 173

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $3 $2 $8 $7 $1 $1 $3 $3 Interest cost 10 13 32 37 2 2 5 6 Expected return on plan assets (17 ) (15 ) (52 ) (45 ) (1 ) (1 ) (4 ) (4 ) Amortization of actuarial loss 9 9 26 27 — 1 2 2 Settlement losses (a) — — 4 — — — — — $5 $9 $18 $26 $2 $3 $6 $7 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2 $1 $5 $4 $— $— $1 $1 Interest cost 5 6 15 17 1 1 2 3 Expected return on plan assets (8 ) (7 ) (24 ) (21 ) (1 ) (1 ) (3 ) (3 ) Amortization of actuarial loss 4 4 11 12 — 1 1 1 $3 $4 $7 $12 $— $1 $1 $2 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1 $1 $3 $3 $— $— $1 $1 Interest cost 5 5 14 16 1 1 2 3 Expected return on plan assets (8 ) (6 ) (23 ) (20 ) (1 ) — (1 ) (1 ) Amortization of actuarial loss 4 4 12 13 1 — 2 1 $2 $4 $6 $12 $1 $1 $4 $4 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $5 $8 $10 $16 $3 $4 $6 $9 $2 $3 $4 $6 Income tax benefits 1 2 3 4 1 1 2 2 — 1 1 2
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30 , 2020 , 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. As of September 30, 2020 , 276,070 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2020
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196 $134 Revisions in estimated cash flows 1 — Liabilities settled (7 ) (5 ) Liabilities incurred (a) 38 38 Accretion expense 5 4 Balance, September 30 $233 $171 (a) During the nine months ended September 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North, Golden Plains and Richland wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the nine months ended September 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196 $134 Revisions in estimated cash flows 1 — Liabilities settled (7 ) (5 ) Liabilities incurred (a) 38 38 Accretion expense 5 4 Balance, September 30 $233 $171 (a) During the nine months ended September 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North, Golden Plains and Richland wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2020 , 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 14,365 2020-2021 218,581 2020-2028 8,151 2020-2023 6,174 2020-2022 IPL 5,401 2020-2021 114,747 2020-2028 3,373 2020-2023 — — WPL 8,964 2020-2021 103,834 2020-2027 4,778 2020-2023 6,174 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $33 $16 $23 $12 $10 $4 Non-current derivative assets 15 11 11 10 4 1 Current derivative liabilities 6 19 2 9 4 10 Non-current derivative liabilities 13 19 6 9 7 10

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $36 $13 $194 $215 Total net gains included in changes in net assets (realized/unrealized) — 13 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (5 ) (3 ) 7 22 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $13 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $21 $12 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 8 7 — — Transfers out of Level 3 — 3 — — Purchases 14 14 — — Sales (1 ) — — — Settlements (a) (12 ) (14 ) 13 118 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $8 $10 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $32 $9 $194 $215 Total net gains (losses) included in changes in net assets (realized/unrealized) (1 ) 12 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (4 ) (2 ) 7 22 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $18 $9 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 7 9 — — Transfers out of Level 3 — 2 — — Purchases 11 9 — — Sales (1 ) — — — Settlements (a) (9 ) (11 ) 13 118 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $7 $10 $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2
IPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $36 $13 $194 $215 Total net gains included in changes in net assets (realized/unrealized) — 13 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (5 ) (3 ) 7 22 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $13 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $21 $12 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 8 7 — — Transfers out of Level 3 — 3 — — Purchases 14 14 — — Sales (1 ) — — — Settlements (a) (12 ) (14 ) 13 118 Ending balance, September 30 $30 $22 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $8 $10 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2020 2019 2020 2019 Beginning balance, July 1 $32 $9 $194 $215 Total net gains (losses) included in changes in net assets (realized/unrealized) (1 ) 12 — — Transfers out of Level 3 — (1 ) — — Sales (1 ) — — — Settlements (a) (4 ) (2 ) 7 22 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($1 ) $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2020 2019 2020 2019 Beginning balance, January 1 $18 $9 $188 $119 Total net gains included in changes in net assets (realized/unrealized) 7 9 — — Transfers out of Level 3 — 2 — — Purchases 11 9 — — Sales (1 ) — — — Settlements (a) (9 ) (11 ) 13 118 Ending balance, September 30 $26 $18 $201 $237 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $7 $10 $— $— (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2
WPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 48 — 17 31 48 27 — 5 22 27 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 19 — 18 1 19 38 — 37 1 38 Long-term debt (incl. current maturities) 6,581 — 7,849 2 7,851 6,190 — 6,918 2 6,920 IPL September 30, 2020 December 31, 2019 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 $183 $183 $— $— $183 $5 $5 $— $— $5 Derivatives 34 — 7 27 34 22 — 3 19 22 Deferred proceeds 201 — — 201 201 188 — — 188 188 Liabilities: Derivatives 8 — 7 1 8 18 — 17 1 18 Long-term debt (incl. current maturities) 3,344 — 3,987 — 3,987 3,147 — 3,489 — 3,489 WPL September 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $14 $— $10 $4 $14 $5 $— $2 $3 $5 Liabilities: Derivatives 11 — 11 — 11 20 — 20 — 20 Long-term debt (incl. current maturities) 2,130 — 2,667 — 2,667 1,933 — 2,268 — 2,268
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2020 $18 $12 $17 $9 $1 $3 December 31, 2019 15 7 14 5 1 2

Commitments And Contingencies (

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2020 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At September 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $9 - $24 Current and non-current environmental liabilities 16 13
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2020 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At September 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $9 - $24 Current and non-current environmental liabilities 16 13
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2020 , related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Natural gas $983 $508 $475 Coal (a) 125 70 55 Other (b) 111 49 31 $1,219 $627 $561 (a) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of September 30, 2020 regarding expected future usage, which is subject to change. (b) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2020 .

Segments Of Business (Tables)

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2020 Revenues $852 $42 $10 $904 $16 $920 Operating income (loss) 251 (1 ) 1 251 21 272 Net income attributable to Alliant Energy common shareowners 221 25 246 Three Months Ended September 30, 2019 Revenues $916 $42 $11 $969 $21 $990 Operating income (loss) 284 (5 ) 3 282 8 290 Net income attributable to Alliant Energy common shareowners 217 9 226 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2020 Revenues $2,257 $253 $32 $2,542 $57 $2,599 Operating income 549 48 5 602 26 628 Net income attributable to Alliant Energy common shareowners 510 40 550 Nine Months Ended September 30, 2019 Revenues $2,350 $323 $33 $2,706 $62 $2,768 Operating income 543 47 5 595 22 617 Net income attributable to Alliant Energy common shareowners 422 24 446 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $519 $24 $10 $553 Operating income 159 1 2 162 Net income available for common stock 148 Three Months Ended September 30, 2019 Revenues $561 $25 $11 $597 Operating income (loss) 175 (4 ) 3 174 Net income available for common stock 141 Nine Months Ended September 30, 2020 Revenues $1,332 $141 $31 $1,504 Operating income 308 34 5 347 Net income available for common stock 290 Nine Months Ended September 30, 2019 Revenues $1,373 $188 $32 $1,593 Operating income 291 26 5 322 Net income available for common stock 239 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2020 Revenues $333 $18 $— $351 Operating income (loss) 92 (2 ) (1 ) 89 Net income 73 Three Months Ended September 30, 2019 Revenues $355 $17 $— $372 Operating income (loss) 109 (1 ) — 108 Net income 76 Nine Months Ended September 30, 2020 Revenues $925 $112 $1 $1,038 Operating income 241 14 — 255 Net income 220 Nine Months Ended September 30, 2019 Revenues $977 $135 $1 $1,113 Operating income 252 21 — 273 Net income 183

Related Parties (Tables)

Related Parties (Tables)	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC billings to WPL $27 $28 $80 $82 WPL billings to ATC 2 3 8 10
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $53 $47 $134 $137 $41 $36 $108 $104 Sales credited 10 23 35 50 — 2 4 6 Purchases billed 110 93 248 251 39 32 79 91
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2020 December 31, 2019 September 30, 2020 December 31, 2019 Net payables to Corporate Services $119 $112 $77 $85
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2020 2019 2020 2019 ATC billings to WPL $27 $28 $80 $82 WPL billings to ATC 2 3 8 10

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 183	$ 5
Money market fund investments interest rate, percentage	0.10%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 183	5
Money market fund investments interest rate, percentage	0.10%
Credit Losses ASU [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax		12
New accounting standard, cumulative effect adjustment to retained earnings, after-tax		$ 9

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)	Aug. 31, 2020customer	Jun. 30, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2020USD ($)
Regulatory Matters [Line Items]
Credits issued to customers				$ (72)	$ (12)
Electric transmission cost recovery [Member] | IPL [Member]
Regulatory Matters [Line Items]
Credits issued to customers			$ 42
DAEC PPA [Member]
Regulatory Matters [Line Items]
Buyout payment	$ 110
PPA term amendment	5 years
Derecho windstorm [Member]
Regulatory Matters [Line Items]
Net regulatory liability, derecho windstorm	$ 7			7
Derecho windstorm [Member] | IPL [Member]
Regulatory Matters [Line Items]
Number of customers without power, derecho windstorm (number of customers) | customer		250,000
Derecho windstorm repair and rebuilding costs	$ 130			$ 130
Derecho windstorm [Member] | Forecast [Member] | IPL [Member]
Regulatory Matters [Line Items]
Derecho windstorm repair and rebuilding costs						$ 140

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory assets	$ 1,836	$ 1,845
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	877	818
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	492	524
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	118	134
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	115	112
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	110	108
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	20	39
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19	21
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	89
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,418	1,400
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	829	777
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	247	263
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	88
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	76
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	110	108
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	8	18
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19	21
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	47	49
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	418	445
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	48	41
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	245	261
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	39	46
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	36	36
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	12	21
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 38	$ 40

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,351	$ 1,424
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	746	836
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	371	388
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62	88
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	20
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36	0
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	24
WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	22
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	52	46
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	691	715
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	334	351
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	241	257
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30	51
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27	17
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	19	9
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	30
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	660	709
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	412	485
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	130	131
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32	37
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	13	3
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	15
WPL [Member] | WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	22
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 12	$ 16

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Sep. 30, 2020USD ($)
Receivables [Line Items]
Available capacity	$ 109
Outstanding receivables past due	$ 27

Receivables (Details of Account

Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Receivables [Line Items]
Customer	$ 95	$ 92
Unbilled utility revenues	62	82
Deferred proceeds	201	188
Other	54	47
Allowance for expected credit losses	(13)	(7)
Accounts receivable, less allowance for expected credit losses	399	402
IPL [Member]
Receivables [Line Items]
Customer	0	0
Unbilled utility revenues	0	0
Deferred proceeds	201	188
Other	20	16
Allowance for expected credit losses	(2)	(1)
Accounts receivable, less allowance for expected credit losses	219	203
WPL [Member]
Receivables [Line Items]
Customer	86	84
Unbilled utility revenues	62	82
Other	33	31
Allowance for expected credit losses	(11)	(6)
Accounts receivable, less allowance for expected credit losses	$ 170	$ 191

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 1	$ 103	$ 96	$ 108
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 1	$ 45	$ 12	$ 43

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Receivables [Line Items]
Fair value of deferred proceeds	$ 201	$ 188
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	201	188
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	148	125
Unbilled utility revenues	67	95
Other receivables	0	1
Receivables sold to third party	215	221
Less: cash proceeds	1	27
Deferred proceeds	214	194
Less: allowance for expected credit losses	13	6
Fair value of deferred proceeds	$ 201	$ 188

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Receivables [Line Items]
Collections	$ 561	$ 592	$ 1,555	$ 1,636
Write-offs, net of recoveries	$ 1	$ 3	$ 4	$ 11

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (15)	$ (12)	$ (46)	$ (35)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(11)	(11)	(36)	(30)
Non-utility wind farm in Oklahoma [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(2)	0	(6)	(3)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (2)	$ (1)	$ (4)	$ (2)

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Nov. 30, 2019	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Common Equity [Line Items]
Proceeds from issuance of common stock, net		$ 6		$ 125	$ 241	$ 185
Equity Forward Agreements [Member]
Common Equity [Line Items]
Common stock to be issued, equity forward agreements (in shares)	4,275,127
Forward sales price (in dollars per share)	$ 52.235		$ 51.98
Proceeds from issuance of common stock, net			$ 222
Common stock issued during the period, equity forward agreements (in shares)			4,275,127		4,275,127

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details) - shares	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2020 (in shares)	245,022,800	245,022,800
Shareowner Direct Plan (in shares)		364,531
Equity-based compensation plans (in shares)		98,205
Shares outstanding, September 30, 2020 (in shares)		249,760,663
Equity Forward Agreements [Member]
Common Stock Oustanding [Roll Forward]
Equity forward agreements (in shares)	4,275,127	4,275,127

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 5,205
Beginning balance	$ 5,748	$ 4,900	5,405	$ 4,786
Net income attributable to common shareowners	246	226	550	446
Net income	249	229	558	454
Common stock dividends	(94)	(85)	(281)	(253)
Equity forward settlements and Shareowner Direct Plan issuances	6	125	241	185
Equity-based compensation plans and other	3	3	5	6
Adoption of new accounting standard, net of tax			(9)
Other comprehensive loss, net of tax			(2)	(1)
Ending balance	5,709		5,709
Ending balance	$ 5,909	$ 5,169	$ 5,909	$ 5,169
Common stock dividends (in dollars per share)	$ 0.38	$ 0.355	$ 1.14	$ 1.065
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 2	$ 2	$ 2	$ 2
Ending balance	2	2	2	2
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,683	2,109	2,446	2,046
Equity forward settlements and Shareowner Direct Plan issuances	6	125	241	185
Equity-based compensation plans and other	4	3	6	6
Ending balance	2,693	2,237	2,693	2,237
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,874	2,598	2,766	2,546
Net income attributable to common shareowners	246	226	550	446
Common stock dividends	(94)	(85)	(281)	(253)
Ending balance	3,026	2,739	3,026	2,739
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(1)	1	1	2
Other comprehensive loss, net of tax			(2)	(1)
Ending balance	(1)	1	(1)	1
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(10)	(10)	(10)	(10)
Equity-based compensation plans and other	(1)		(1)
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			3,272
Beginning balance	3,671	3,345	3,472	3,231
Net income attributable to common shareowners	148	141	290	239
Net income	151	144	298	247
Common stock dividends	(59)	(42)	(177)	(126)
Capital contributions from parent	170		345	100
Ending balance	3,730		3,730
Ending balance	3,930	3,444	3,930	3,444
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	2,523	2,323	2,348	2,223
Capital contributions from parent	170		345	100
Ending balance	2,693	2,323	2,693	2,323
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	915	789	891	775
Net income attributable to common shareowners	148	141	290	239
Common stock dividends	(59)	(42)	(177)	(126)
Ending balance	1,004	888	1,004	888
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			2,364
Beginning balance	2,452	2,185	2,364	2,150
Net income	73	76	220	183
Common stock dividends	(43)	(36)	(127)	(108)
Capital contributions from parent		100	25	100
Ending balance	2,482		2,482
Ending balance	2,482	2,325	2,482	2,325
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	1,459	1,309	1,434	1,309
Capital contributions from parent		100	25	100
Ending balance	1,459	1,409	1,459	1,409
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	927	810	864	775
Net income	73	76	220	183
Common stock dividends	(43)	(36)	(127)	(108)
Ending balance	$ 957	$ 850	957	$ 850
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 (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended			9 Months Ended
	Jun. 30, 2020	Apr. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Debt [Line Items]
Payments to retire long-term debt				$ 654	$ 253
IPL [Member]
Debt [Line Items]
Payments to retire long-term debt				200	0
WPL [Member]
Debt [Line Items]
Payments to retire long-term debt				$ 150	$ 250
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through March 2022 [Member] | Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt			$ 300
Interest rate, percent				1.00%
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through April 2020 [Member] | Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Payments to retire long-term debt			$ 300
Debentures [Member] | 3.65% debenture, due 2050 [Member] | WPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt		$ 350
Interest rate, percent				3.65%
Debentures [Member] | 4.6% debenture, due 2020 [Member] | WPL [Member]
Debt [Line Items]
Interest rate, percent	4.60%
Payments to retire long-term debt	$ 150
Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member] | IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 400
Interest rate, percent				2.30%
Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member] | IPL [Member]
Debt [Line Items]
Interest rate, percent	3.65%
Payments to retire long-term debt	$ 200

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Sep. 30, 2020USD ($)
Debt [Line Items]
Amount outstanding	$ 422
Weighted average interest rates	0.20%
Available credit facility capacity	$ 578
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 139
Weighted average interest rates	0.10%
Available credit facility capacity	$ 161

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 422	$ 472	$ 463	$ 601
Average amount outstanding (based on daily outstanding balances)	$ 252	$ 400	$ 252	$ 476
Weighted average interest rates	0.20%	2.50%	1.10%	2.60%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 0	$ 8	$ 50
Average amount outstanding (based on daily outstanding balances)	0	0	$ 0	$ 0
Weighted average interest rates			0.50%	2.80%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	139	90	$ 212	$ 195
Average amount outstanding (based on daily outstanding balances)	$ 83	$ 27	$ 86	$ 102
Weighted average interest rates	0.20%	2.30%	1.20%	2.50%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 920	$ 990	$ 2,599	$ 2,768
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	852	916	2,257	2,350
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	328	332	845	840
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	210	231	556	583
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	241	264	648	686
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	50	127	137
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	39	81	104
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	42	42	253	323
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	20	146	187
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	70	90
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	3	8	10
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	9	29	36
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	11	32	33
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	9	27	27
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2	5	6
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	21	57	62
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	21	57	62
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	553	597	1,504	1,593
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	519	561	1,332	1,373
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	189	196	472	470
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	142	158	371	386
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	149	158	384	392
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17	18	44	49
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	31	61	76
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	25	141	188
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	12	79	109
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	6	38	50
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	5	7
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	5	19	22
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	11	31	32
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	9	27	27
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2	4	5
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	351	372	1,038	1,113
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	333	355	925	977
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	139	136	373	370
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	68	73	185	197
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	92	106	264	294
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	32	83	88
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	8	20	28
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18	17	112	135
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	8	67	78
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	4	32	40
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	3	3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	4	10	14
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	1
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 1	$ 1

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Effective Tax Rate [Line Items]
Overall income tax rate	(9.00%)	9.00%	(9.00%)	10.00%
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(14.00%)	5.00%	(14.00%)	4.00%
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(7.00%)	18.00%	(8.00%)	18.00%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2020USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 371
Tax credits, carryforward amount	446
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	343
Tax credits, carryforward amount	252
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Tax credits, carryforward amount	173
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	623
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	10
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 7
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 4
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 3
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	276,070

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 2	$ 8	$ 7
Interest cost	10	13	32	37
Expected return on plan assets	(17)	(15)	(52)	(45)
Amortization of actuarial loss	9	9	26	27
Settlement losses	0	0	4	0
Total	5	9	18	26
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	3
Interest cost	2	2	5	6
Expected return on plan assets	(1)	(1)	(4)	(4)
Amortization of actuarial loss	0	1	2	2
Settlement losses	0	0	0	0
Total	2	3	6	7
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1	5	4
Interest cost	5	6	15	17
Expected return on plan assets	(8)	(7)	(24)	(21)
Amortization of actuarial loss	4	4	11	12
Total	3	4	7	12
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	1	1	2	3
Expected return on plan assets	(1)	(1)	(3)	(3)
Amortization of actuarial loss	0	1	1	1
Total	0	1	1	2
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	3
Interest cost	5	5	14	16
Expected return on plan assets	(8)	(6)	(23)	(20)
Amortization of actuarial loss	4	4	12	13
Total	2	4	6	12
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	1	1	2	3
Expected return on plan assets	(1)	0	(1)	(1)
Amortization of actuarial loss	1	0	2	1
Total	$ 1	$ 1	$ 4	$ 4

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Compensation expense	$ 5	$ 8	$ 10	$ 16
Income tax benefits	1	2	3	4
IPL [Member]
Compensation expense	3	4	6	9
Income tax benefits	1	1	2	2
WPL [Member]
Compensation expense	2	3	4	6
Income tax benefits	$ 0	$ 1	$ 1	$ 2

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	9 Months Ended
	Sep. 30, 2020$ / sharesshares
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	55,303
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 64.04
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	55,303
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 59.47
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	60,284
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 59.49

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 196
Revisions in estimated cash flows	1
Liabilities settled	(7)
Liabilities incurred	38
Accretion expense	5
Balance, September 30	233
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	134
Revisions in estimated cash flows	0
Liabilities settled	(5)
Liabilities incurred	38
Accretion expense	4
Balance, September 30	$ 171

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands, T in Thousands, MWh in Thousands, Dekatherms in Thousands	9 Months Ended
	Sep. 30, 2020DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	14,365
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	5,401
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	8,964
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	218,581
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	114,747
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	103,834
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	8,151
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	3,373
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,778
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	6,174
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	6,174

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 33	$ 16
Non-current derivative assets	15	11
Current derivative liabilities	6	19
Non-current derivative liabilities	13	19
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	23	12
Non-current derivative assets	11	10
Current derivative liabilities	2	9
Non-current derivative liabilities	6	9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	10	4
Non-current derivative assets	4	1
Current derivative liabilities	4	10
Non-current derivative liabilities	$ 7	$ 10

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets:
Money market fund investments	$ 183	$ 5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	7,851	6,920
IPL [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	3,987	3,489
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,667	2,268
Commodity Contracts [Member]
Assets:
Derivatives	48	27
Liabilities:
Derivatives	19	38
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	22
Liabilities:
Derivatives	8	18
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	14	5
Liabilities:
Derivatives	11	20
Level 1 [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	183	5
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)	7,849	6,918
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,987	3,489
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,667	2,268
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	17	5
Liabilities:
Derivatives	18	37
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	7	3
Liabilities:
Derivatives	7	17
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	10	2
Liabilities:
Derivatives	11	20
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	2	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	201	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	31	22
Liabilities:
Derivatives	1	1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	27	19
Liabilities:
Derivatives	1	1
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	4	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	6,581	6,190
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	3,344	3,147
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,130	1,933
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	48	27
Liabilities:
Derivatives	19	38
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	22
Liabilities:
Derivatives	8	18
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	14	5
Liabilities:
Derivatives	$ 11	$ 20

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 36	$ 13	$ 21	$ 12
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	13	8	7
Transfers out of Level 3	0	(1)	0	3
Purchases			14	14
Sales	(1)	0	(1)	0
Settlements	(5)	(3)	(12)	(14)
Ending balance	30	22	30	22
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	(1)	13	8	10
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	32	9	18	9
Total net gains (losses) included in changes in net assets (realized/unrealized)	(1)	12	7	9
Transfers out of Level 3	0	(1)	0	2
Purchases			11	9
Sales	(1)	0	(1)	0
Settlements	(4)	(2)	(9)	(11)
Ending balance	26	18	26	18
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	(1)	12	7	10
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	194	215	188	119
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	7	22	13	118
Ending balance	201	237	201	237
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	0	0	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	194	215	188	119
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	7	22	13	118
Ending balance	201	237	201	237
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 30	$ 36	$ 21	$ 22	$ 13	$ 12
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	18		15
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	12		7
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	26	$ 32	18	$ 18	$ 9	$ 9
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	17		14
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	9		5
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	1		1
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 3		$ 2

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	May 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Mar. 31, 2020
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,219
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			627
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			561
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			21
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			18
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum		$ 74	74
Indemnification Agreement [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum		17	17
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum		17	$ 17
Credit Losses ASU [Member]
Commitments and Contingencies [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax				$ 12
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent			6.00%
Obligations, maximum		68	$ 68
Credit loss liability		5	5		$ 20
Credit loss expense		$ 15	7
Whiting Petroleum Affiliate [Member] | Credit Losses ASU [Member]
Commitments and Contingencies [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax				$ 12
FederalEnergyRegulatoryCommission [Member]
Commitments and Contingencies [Line Items]
MISO base return on equity, percentage	10.02%			9.88%
FederalEnergyRegulatoryCommission [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Refunds related to MISO base return on equity complaints			15
FederalEnergyRegulatoryCommission [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Refunds related to MISO base return on equity complaints			$ 5

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,219
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	627
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	561
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	983
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	508
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	475
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	125
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	70
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	55
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	111
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	49
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 31

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 16
IPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	13
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	12
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	9
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	29
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 24

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 920	$ 990	$ 2,599	$ 2,768
Operating income (loss)	272	290	628	617
Net income attributable to common shareowners	246	226	550	446
Net income	249	229	558	454
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	553	597	1,504	1,593
Operating income (loss)	162	174	347	322
Net income attributable to common shareowners	148	141	290	239
Net income	151	144	298	247
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	351	372	1,038	1,113
Operating income (loss)	89	108	255	273
Net income	73	76	220	183
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	852	916	2,257	2,350
Operating income (loss)	251	284	549	543
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	519	561	1,332	1,373
Operating income (loss)	159	175	308	291
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	333	355	925	977
Operating income (loss)	92	109	241	252
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	42	42	253	323
Operating income (loss)	(1)	(5)	48	47
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	24	25	141	188
Operating income (loss)	1	(4)	34	26
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	18	17	112	135
Operating income (loss)	(2)	(1)	14	21
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10	11	32	33
Operating income (loss)	1	3	5	5
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10	11	31	32
Operating income (loss)	2	3	5	5
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	1	1
Operating income (loss)	(1)	0	0	0
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	904	969	2,542	2,706
Operating income (loss)	251	282	602	595
Net income attributable to common shareowners	221	217	510	422
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	16	21	57	62
Operating income (loss)	21	8	26	22
Net income attributable to common shareowners	$ 25	$ 9	$ 40	$ 24

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
WPL Owed ATC LLC [Member]
Related Party Transactions [Line Items]
Net amounts owed		$ 9	$ 9
WPL [Member]
Related Party Transactions [Line Items]
Receipt of construction deposits	$ 46

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 53	$ 47	$ 134	$ 137
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	41	36	108	104
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	10	23	35	50
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	0	2	4	6
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	110	93	248	251
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 39	$ 32	$ 79	$ 91

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 119	$ 112
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 77	$ 85

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 27	$ 28	$ 80	$ 82
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 2	$ 3	$ 8	$ 10