Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 39	$ 54
Accounts receivable, less allowance for expected credit losses	440	412
Production fuel, at weighted average cost	51	66
Gas stored underground, at weighted average cost	82	46
Materials and supplies, at weighted average cost	113	105
Regulatory assets	104	81
Other	240	123
Total current assets	1,069	887
Property, plant and equipment, net	14,987	14,336
Investments:
ATC Holdings	338	331
Other	179	154
Total investments	517	485
Other assets:
Regulatory assets	1,836	1,929
Deferred charges and other	144	73
Total other assets	1,980	2,002
Total assets	18,553	17,710
Current liabilities:
Current maturities of long-term debt	633	8
Commercial paper	515	389
Accounts payable	436	377
Accrued taxes	58	67
Regulatory liabilities	186	249
Other	226	207
Total current liabilities	2,054	1,297
Long-term debt, net (excluding current portion)	6,735	6,769
Other liabilities:
Deferred tax liabilities	1,927	1,814
Regulatory liabilities	1,085	1,057
Pension and other benefit obligations	374	511
Other	388	374
Total other liabilities	3,774	3,756
Commitments and contingencies (Note 17)
Common equity:
Common stock	3	2
Additional paid-in capital	2,749	2,704
Retained earnings	3,250	2,994
Accumulated other comprehensive loss	0	(1)
Shares in deferred compensation trust - 383,532 and 380,542 shares at a weighted average cost of $30.59 and $28.73 per share	(12)	(11)
Total common equity	5,990	5,688
Cumulative preferred stock of Interstate Power and Light Company	0	200
Total equity	5,990	5,888
Total liabilities and equity	18,553	17,710
IPL [Member]
Current assets:
Cash and cash equivalents	34	50
Accounts receivable, less allowance for expected credit losses	241	210
Income taxes refunds receivable	8	26
Production fuel, at weighted average cost	29	48
Gas stored underground, at weighted average cost	40	20
Materials and supplies, at weighted average cost	70	63
Regulatory assets	73	52
Other	69	27
Total current assets	564	496
Property, plant and equipment, net	7,983	7,889
Other assets:
Regulatory assets	1,370	1,431
Deferred charges and other	79	33
Total other assets	1,449	1,464
Total assets	9,996	9,849
Current liabilities:
Current maturities of long-term debt	0	0
Commercial paper	0	0
Accounts payable	173	162
Accounts payable to associated companies	39	45
Accrued taxes	56	54
Regulatory liabilities	84	103
Accrued interest	36	34
Other	67	49
Total current liabilities	455	447
Long-term debt, net (excluding current portion)	3,643	3,345
Other liabilities:
Deferred tax liabilities	1,083	1,035
Regulatory liabilities	607	573
Pension and other benefit obligations	127	186
Other	312	299
Total other liabilities	2,129	2,093
Commitments and contingencies (Note 17)
Common equity:
Common stock	33	33
Additional paid-in capital	2,807	2,752
Retained earnings	929	979
Total common equity	3,769	3,764
Cumulative preferred stock of Interstate Power and Light Company	0	200
Total equity	3,769	3,964
Total liabilities and equity	9,996	9,849
WPL [Member]
Current assets:
Cash and cash equivalents	2	3
Accounts receivable, less allowance for expected credit losses	188	192
Production fuel, at weighted average cost	23	18
Gas stored underground, at weighted average cost	42	26
Materials and supplies, at weighted average cost	41	40
Regulatory assets	31	29
Prepaid gross receipts tax	40	42
Other	86	12
Total current assets	453	362
Property, plant and equipment, net	6,538	6,022
Other assets:
Regulatory assets	466	498
Deferred charges and other	61	30
Total other assets	527	528
Total assets	7,518	6,912
Current liabilities:
Current maturities of long-term debt	250	0
Commercial paper	236	257
Accounts payable	190	154
Accounts payable to associated companies	39	35
Regulatory liabilities	102	146
Other	73	82
Total current liabilities	890	674
Long-term debt, net (excluding current portion)	2,179	2,130
Other liabilities:
Deferred tax liabilities	753	702
Regulatory liabilities	478	484
Pension and other benefit obligations	159	222
Other	236	222
Total other liabilities	1,626	1,630
Commitments and contingencies (Note 17)
Common equity:
Common stock	66	66
Additional paid-in capital	1,704	1,459
Retained earnings	1,053	953
Total common equity	2,823	2,478
Total equity	2,823	2,478
Total liabilities and equity	$ 7,518	$ 6,912