Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 208.1	$ 16.3
Accounts receivable, less allowance for expected credit losses	386.5	402.1
Production fuel, at weighted average cost	78.0	77.7
Gas stored underground, at weighted average cost	36.8	49.1
Materials and supplies, at weighted average cost	107.0	100.5
Regulatory assets	94.5	86.4
Other	133.4	143.4
Total current assets	1,044.3	875.5
Property, plant and equipment, net	13,936.4	13,527.1
Investments:
ATC Holdings	326.1	320.1
Other	147.1	147.7
Total investments	473.2	467.8
Other assets:
Regulatory assets	1,748.5	1,758.3
Deferred charges and other	67.3	72.0
Total other assets	1,815.8	1,830.3
Total assets	17,269.7	16,700.7
Current liabilities:
Current maturities of long-term debt	7.4	657.2
Commercial paper	185.4	337.4
Accounts payable	429.9	422.3
Regulatory liabilities	211.4	212.0
Other	386.8	425.2
Total current liabilities	1,220.9	2,054.1
Long-term debt, net (excluding current portion)	6,572.4	5,533.0
Other liabilities:
Deferred tax liabilities	1,761.3	1,714.0
Regulatory liabilities	1,159.6	1,211.6
Pension and other benefit obligations	450.2	484.0
Other	357.0	298.9
Total other liabilities	3,728.1	3,708.5
Commitments and contingencies (Note 13)
Common equity:
Common stock	2.5	2.5
Additional paid-in capital	2,683.1	2,445.9
Retained earnings	2,873.5	2,765.4
Accumulated other comprehensive income (loss)	(0.6)	1.3
Shares in deferred compensation trust - 367,493 and 381,232 shares at a weighted average cost of $27.86 and $26.24 per share	(10.2)	(10.0)
Total common equity	5,548.3	5,205.1
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	5,748.3	5,405.1
Total liabilities and equity	17,269.7	16,700.7
IPL [Member]
Current assets:
Cash and cash equivalents	203.5	9.3
Accounts receivable, less allowance for expected credit losses	208.9	202.8
Production fuel, at weighted average cost	54.8	47.1
Gas stored underground, at weighted average cost	10.4	21.7
Materials and supplies, at weighted average cost	60.4	55.0
Regulatory assets	54.0	43.5
Other	32.5	30.0
Total current assets	624.5	409.4
Property, plant and equipment, net	7,666.3	7,480.7
Other assets:
Regulatory assets	1,350.9	1,355.8
Deferred charges and other	37.9	31.6
Total other assets	1,388.8	1,387.4
Total assets	9,679.6	9,277.5
Current liabilities:
Current maturities of long-term debt	0.0	200.0
Accounts payable	207.3	207.0
Regulatory liabilities	131.1	115.9
Other	293.8	307.6
Total current liabilities	632.2	830.5
Long-term debt, net (excluding current portion)	3,343.5	2,947.3
Other liabilities:
Deferred tax liabilities	1,012.7	1,008.0
Regulatory liabilities	586.8	598.8
Pension and other benefit obligations	160.1	167.7
Other	273.2	253.4
Total other liabilities	2,032.8	2,027.9
Commitments and contingencies (Note 13)
Common equity:
Common stock	33.4	33.4
Additional paid-in capital	2,522.8	2,347.8
Retained earnings	914.9	890.6
Total common equity	3,471.1	3,271.8
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	3,671.1	3,471.8
Total liabilities and equity	9,679.6	9,277.5
WPL [Member]
Current assets:
Cash and cash equivalents	3.2	4.4
Accounts receivable, less allowance for expected credit losses	166.9	190.9
Production fuel, at weighted average cost	23.1	30.6
Gas stored underground, at weighted average cost	26.4	27.4
Materials and supplies, at weighted average cost	44.3	43.1
Regulatory assets	40.5	42.9
Other	52.1	103.4
Total current assets	356.5	442.7
Property, plant and equipment, net	5,867.2	5,638.3
Other assets:
Regulatory assets	397.6	402.5
Deferred charges and other	27.1	23.0
Total other assets	424.7	425.5
Total assets	6,648.4	6,506.5
Current liabilities:
Current maturities of long-term debt	0.0	150.0
Commercial paper	37.9	168.2
Accounts payable	183.0	159.9
Accounts payable to associated companies	28.9	41.8
Regulatory liabilities	80.3	96.1
Other	79.5	74.3
Total current liabilities	409.6	690.3
Long-term debt, net (excluding current portion)	2,129.4	1,782.7
Other liabilities:
Deferred tax liabilities	667.4	626.2
Regulatory liabilities	572.8	612.8
Finance lease obligations - Sheboygan Falls Energy Facility	46.7	51.4
Pension and other benefit obligations	201.8	210.8
Other	168.9	168.7
Total other liabilities	1,657.6	1,669.9
Commitments and contingencies (Note 13)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,459.0	1,434.0
Retained earnings	926.6	863.4
Total common equity	2,451.8	2,363.6
Total equity	2,451.8	2,363.6
Total liabilities and equity	$ 6,648.4	$ 6,506.5