Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 54	$ 16
Accounts receivable, less allowance for expected credit losses	412	402
Production fuel, at weighted average cost	66	78
Gas stored underground, at weighted average cost	46	49
Materials and supplies, at weighted average cost	105	100
Regulatory assets	81	87
Other	123	144
Total current assets	887	876
Property, plant and equipment, net	14,336	13,527
Investments:
ATC Holdings	331	320
Other	154	148
Total investments	485	468
Other assets:
Regulatory assets	1,929	1,758
Deferred charges and other	73	72
Total other assets	2,002	1,830
Total assets	17,710	16,701
Current liabilities:
Current maturities of long-term debt	8	657
Commercial paper	389	337
Accounts payable	377	422
Accrued taxes	67	70
Regulatory liabilities	249	212
Other	207	356
Total current liabilities	1,297	2,054
Long-term debt, net (excluding current portion)	6,769	5,533
Other liabilities:
Deferred tax liabilities	1,814	1,714
Regulatory liabilities	1,057	1,212
Pension and other benefit obligations	511	484
Other	374	299
Total other liabilities	3,756	3,709
Commitments and contingencies (Note 17)
Common equity:
Common stock	2	2
Additional paid-in capital	2,704	2,446
Retained earnings	2,994	2,766
Accumulated other comprehensive income (loss)	(1)	1
Shares in deferred compensation trust - 380,542 and 381,232 shares at a weighted average cost of $28.73 and $26.24 per share	(11)	(10)
Total common equity	5,688	5,205
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	5,888	5,405
Total liabilities and equity	17,710	16,701
IPL [Member]
Current assets:
Cash and cash equivalents	50	9
Accounts receivable, less allowance for expected credit losses	210	203
Income taxes refunds receivable	26	11
Production fuel, at weighted average cost	48	47
Gas stored underground, at weighted average cost	20	22
Materials and supplies, at weighted average cost	63	55
Regulatory assets	52	44
Other	27	18
Total current assets	496	409
Property, plant and equipment, net	7,889	7,481
Other assets:
Regulatory assets	1,431	1,356
Deferred charges and other	33	31
Total other assets	1,464	1,387
Total assets	9,849	9,277
Current liabilities:
Current maturities of long-term debt	0	200
Commercial paper	0	0
Accounts payable	162	207
Accounts payable to associated companies	45	39
Accrued taxes	54	63
Regulatory liabilities	103	116
Accrued interest	34	37
Other	49	168
Total current liabilities	447	830
Long-term debt, net (excluding current portion)	3,345	2,947
Other liabilities:
Deferred tax liabilities	1,035	1,008
Regulatory liabilities	573	599
Pension and other benefit obligations	186	168
Other	299	253
Total other liabilities	2,093	2,028
Commitments and contingencies (Note 17)
Common equity:
Common stock	33	33
Additional paid-in capital	2,752	2,348
Retained earnings	979	891
Total common equity	3,764	3,272
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,964	3,472
Total liabilities and equity	9,849	9,277
WPL [Member]
Current assets:
Cash and cash equivalents	3	4
Accounts receivable, less allowance for expected credit losses	192	191
Production fuel, at weighted average cost	18	31
Gas stored underground, at weighted average cost	26	27
Materials and supplies, at weighted average cost	40	43
Regulatory assets	29	43
Prepaid gross receipts tax	42	42
Other	12	62
Total current assets	362	443
Property, plant and equipment, net	6,022	5,638
Other assets:
Regulatory assets	498	402
Deferred charges and other	30	24
Total other assets	528	426
Total assets	6,912	6,507
Current liabilities:
Current maturities of long-term debt	0	150
Commercial paper	257	168
Accounts payable	154	160
Accounts payable to associated companies	35	42
Regulatory liabilities	146	96
Other	82	74
Total current liabilities	674	690
Long-term debt, net (excluding current portion)	2,130	1,783
Other liabilities:
Deferred tax liabilities	702	626
Regulatory liabilities	484	613
Finance lease obligations - Sheboygan Falls Energy Facility	42	51
Pension and other benefit obligations	222	211
Other	180	169
Total other liabilities	1,630	1,670
Commitments and contingencies (Note 17)
Common equity:
Common stock	66	66
Additional paid-in capital	1,459	1,434
Retained earnings	953	864
Total common equity	2,478	2,364
Total equity	2,478	2,364
Total liabilities and equity	$ 6,912	$ 6,507