Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 193.7	$ 20.9
Accounts receivable, less allowance for doubtful accounts	451.5	350.4
Production fuel, at weighted average cost	71.1	61.4
Gas stored underground, at weighted average cost	46.1	49.0
Materials and supplies, at weighted average cost	106.9	101.4
Regulatory assets	76.3	79.8
Prepaid gross receipts tax	30.3	42.2
Other	137.1	80.0
Total current assets	1,113.0	785.1
Property, plant and equipment, net	13,131.1	12,462.4
Investments:
ATC Holdings	309.1	293.6
Other	143.9	137.7
Total investments	453.0	431.3
Other assets:
Regulatory assets	1,763.7	1,657.5
Deferred charges and other	72.6	89.7
Total other assets	1,836.3	1,747.2
Total assets	16,533.4	15,426.0
Current liabilities:
Current maturities of long-term debt	656.8	256.5
Commercial paper	349.6	441.2
Accounts payable	497.7	543.3
Regulatory liabilities	188.9	142.7
Other	389.1	260.4
Total current liabilities	2,082.1	1,644.1
Long-term debt, net (excluding current portion)	5,535.1	5,246.3
Other liabilities:
Deferred tax liabilities	1,703.0	1,603.1
Regulatory liabilities	1,262.1	1,350.5
Pension and other benefit obligations	476.3	509.1
Other	305.6	287.2
Total other liabilities	3,747.0	3,749.9
Commitments and contingencies (Note 14)
Common equity:
Common stock	2.4	2.4
Additional paid-in capital	2,236.9	2,045.5
Retained earnings	2,739.1	2,545.9
Accumulated other comprehensive income	1.0	1.7
Shares in deferred compensation trust - 385,343 and 384,580 shares at a weighted average cost of $26.52 and $25.60 per share	(10.2)	(9.8)
Total common equity	4,969.2	4,585.7
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	5,169.2	4,785.7
Total liabilities and equity	16,533.4	15,426.0
IPL [Member]
Current assets:
Cash and cash equivalents	184.0	9.7
Accounts receivable, less allowance for doubtful accounts	258.3	153.5
Production fuel, at weighted average cost	40.3	44.8
Gas stored underground, at weighted average cost	21.6	26.1
Materials and supplies, at weighted average cost	60.3	55.4
Regulatory assets	34.6	39.2
Other	22.1	43.1
Total current assets	621.2	371.8
Property, plant and equipment, net	7,283.9	6,781.5
Other assets:
Regulatory assets	1,369.4	1,239.8
Deferred charges and other	28.1	18.3
Total other assets	1,397.5	1,258.1
Total assets	9,302.6	8,411.4
Current liabilities:
Current maturities of long-term debt	200.0	0.0
Commercial paper	0.0	50.4
Accounts payable	290.0	304.9
Accounts payable to associated companies	40.7	28.8
Regulatory liabilities	95.5	90.0
Accrued taxes	58.7	45.8
Other	197.7	87.2
Total current liabilities	882.6	607.1
Long-term debt, net (excluding current portion)	2,946.8	2,552.3
Other liabilities:
Deferred tax liabilities	974.9	957.3
Regulatory liabilities	638.1	664.9
Pension and other benefit obligations	165.1	178.4
Other	251.0	220.7
Total other liabilities	2,029.1	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	887.9	774.5
Total common equity	3,244.1	3,030.7
Cumulative preferred stock of Interstate Power and Light Company	200.0	200.0
Total equity	3,444.1	3,230.7
Total liabilities and equity	9,302.6	8,411.4
WPL [Member]
Current assets:
Cash and cash equivalents	8.3	8.7
Accounts receivable, less allowance for doubtful accounts	184.3	190.1
Production fuel, at weighted average cost	30.8	16.6
Gas stored underground, at weighted average cost	24.5	22.9
Materials and supplies, at weighted average cost	43.7	42.9
Regulatory assets	41.7	40.6
Prepaid gross receipts tax	30.3	42.2
Other	86.6	20.6
Total current assets	450.2	384.6
Property, plant and equipment, net	5,449.7	5,287.3
Other assets:
Regulatory assets	394.3	417.7
Deferred charges and other	19.5	62.9
Total other assets	413.8	480.6
Total assets	6,313.7	6,152.5
Current liabilities:
Current maturities of long-term debt	150.0	250.0
Commercial paper	0.0	105.5
Accounts payable	151.1	180.9
Regulatory liabilities	93.4	52.7
Other	113.6	105.5
Total current liabilities	508.1	694.6
Long-term debt, net (excluding current portion)	1,782.3	1,584.9
Other liabilities:
Deferred tax liabilities	652.6	582.0
Regulatory liabilities	624.0	685.6
Finance lease obligations - Sheboygan Falls Energy Facility	53.6	60.0
Pension and other benefit obligations	203.5	217.7
Other	164.8	178.2
Total other liabilities	1,698.5	1,723.5
Commitments and contingencies (Note 14)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,409.0	1,309.0
Retained earnings	849.6	774.3
Total common equity	2,324.8	2,149.5
Total equity	2,324.8	2,149.5
Total liabilities and equity	$ 6,313.7	$ 6,152.5