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