Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 170.2	$ 20.9
Accounts receivable, less allowance for doubtful accounts	421.5	350.4
Production fuel, at weighted average cost	67.8	61.4
Gas stored underground, at weighted average cost	32.9	49.0
Materials and supplies, at weighted average cost	105.1	101.4
Regulatory assets	78.7	79.8
Other	151.1	122.2
Total current assets	1,027.3	785.1
Property, plant and equipment, net	12,854.0	12,462.4
Investments:
ATC Holdings	302.3	293.6
Other	141.0	137.7
Total investments	443.3	431.3
Other assets:
Regulatory assets	1,728.2	1,657.5
Deferred charges and other	68.8	89.7
Total other assets	1,797.0	1,747.2
Total assets	16,121.6	15,426.0
Current liabilities:
Current maturities of long-term debt	706.8	256.5
Commercial paper	390.5	441.2
Accounts payable	422.5	543.3
Regulatory liabilities	166.9	142.7
Other	262.3	260.4
Total current liabilities	1,949.0	1,644.1
Long-term debt, net (excluding current portion)	5,438.1	5,246.3
Other liabilities:
Deferred tax liabilities	1,657.9	1,603.1
Regulatory liabilities	1,276.0	1,350.5
Pension and other benefit obligations	487.4	509.1
Other	413.6	287.2
Total other liabilities	3,834.9	3,749.9
Commitments and contingencies (Note 14)
Common equity:
Common stock	2.4	2.4
Additional paid-in capital	2,108.4	2,045.5
Retained earnings	2,597.8	2,545.9
Accumulated other comprehensive income	1.0	1.7
Shares in deferred compensation trust - 380,863 and 384,580 shares at a weighted average cost of $26.22 and $25.60 per share	(10.0)	(9.8)
Total common equity	4,699.6	4,585.7
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	4,899.6	4,785.7
Total liabilities and equity	16,121.6	15,426.0
IPL [Member]
Current assets:
Cash and cash equivalents	5.0	9.7
Accounts receivable, less allowance for doubtful accounts	231.7	153.5
Production fuel, at weighted average cost	37.8	44.8
Gas stored underground, at weighted average cost	11.8	26.1
Materials and supplies, at weighted average cost	58.0	55.4
Regulatory assets	33.8	39.2
Other	21.7	43.1
Total current assets	399.8	371.8
Property, plant and equipment, net	7,080.4	6,781.5
Other assets:
Regulatory assets	1,330.7	1,239.8
Deferred charges and other	19.6	18.3
Total other assets	1,350.3	1,258.1
Total assets	8,830.5	8,411.4
Current liabilities:
Commercial paper	0.0	50.4
Accounts payable	216.8	304.9
Accounts payable to associated companies	43.0	28.8
Regulatory liabilities	82.1	90.0
Accrued taxes	64.7	45.8
Other	87.8	87.2
Total current liabilities	494.4	607.1
Long-term debt, net (excluding current portion)	2,850.5	2,552.3
Other liabilities:
Deferred tax liabilities	971.2	957.3
Regulatory liabilities	637.8	664.9
Pension and other benefit obligations	171.0	178.4
Other	360.5	220.7
Total other liabilities	2,140.5	2,021.3
Commitments and contingencies (Note 14)
Common equity:
Common stock	33.4	33.4
Additional paid-in capital	2,322.8	2,222.8
Retained earnings	788.9	774.5
Total common equity	3,145.1	3,030.7
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	3,345.1	3,230.7
Total liabilities and equity	8,830.5	8,411.4
WPL [Member]
Current assets:
Cash and cash equivalents	163.2	8.7
Accounts receivable, less allowance for doubtful accounts	180.9	190.1
Production fuel, at weighted average cost	30.0	16.6
Gas stored underground, at weighted average cost	21.1	22.9
Materials and supplies, at weighted average cost	44.3	42.9
Regulatory assets	44.9	40.6
Other	108.8	62.8
Total current assets	593.2	384.6
Property, plant and equipment, net	5,377.5	5,287.3
Other assets:
Regulatory assets	397.5	417.7
Deferred charges and other	21.8	62.9
Total other assets	419.3	480.6
Total assets	6,390.0	6,152.5
Current liabilities:
Current maturities of long-term debt	400.0	250.0
Commercial paper	0.0	105.5
Accounts payable	150.0	180.9
Regulatory liabilities	84.8	52.7
Other	109.1	105.5
Total current liabilities	743.9	694.6
Long-term debt, net (excluding current portion)	1,781.8	1,584.9
Other liabilities:
Deferred tax liabilities	615.1	582.0
Regulatory liabilities	638.2	685.6
Finance lease obligations - Sheboygan Falls Energy Facility	55.8	60.0
Pension and other benefit obligations	210.5	217.7
Other	159.5	178.2
Total other liabilities	1,679.1	1,723.5
Commitments and contingencies (Note 14)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,309.0	1,309.0
Retained earnings	810.0	774.3
Total common equity	2,185.2	2,149.5
Total equity	2,185.2	2,149.5
Total liabilities and equity	$ 6,390.0	$ 6,152.5