Disaggregation of Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 3,534.5	$ 3,382.2	$ 3,320.0
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,042.3	1,870.3	1,820.4
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,452.6	1,472.8	1,459.1
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,000.3	2,894.7	2,875.5
Electric [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,731.1	1,598.9	1,569.7
Electric [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,269.2	1,295.8	1,305.8
Electric [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,063.4	1,006.2	1,001.1
Electric [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	590.6	535.6	536.7
Electric [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	472.8	470.6	464.4
Electric [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	735.6	710.3	712.6
Electric [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	486.8	452.7	445.4
Electric [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	248.8	257.6	267.2
Electric [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	888.8	853.1	851.1
Electric [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	500.8	459.7	460.4
Electric [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	388.0	393.4	390.7
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenues	188.4	238.4	256.6
Electric [Member] | Wholesale [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	71.2	95.5	94.2
Electric [Member] | Wholesale [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	117.2	142.9	162.4
Electric [Member] | Other Customer [Member]
Disaggregation of Revenue [Line Items]
Revenues	124.1	86.7	54.1
Electric [Member] | Other Customer [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	81.7	55.4	33.0
Electric [Member] | Other Customer [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	42.4	31.3	21.1
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues	446.6	400.9	355.4
Gas [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	266.2	226.0	204.0
Gas [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	180.4	174.9	151.4
Gas [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	254.4	224.7	197.6
Gas [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	152.3	123.2	110.6
Gas [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	102.1	101.5	87.0
Gas [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	133.0	123.2	109.6
Gas [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	75.9	67.9	61.9
Gas [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	57.1	55.3	47.7
Gas [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	14.9	16.7	15.2
Gas [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	10.2	11.1	10.6
Gas [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	4.7	5.6	4.6
Gas [Member] | Other Customer [Member]
Disaggregation of Revenue [Line Items]
Revenues	44.3	36.3	33.0
Gas [Member] | Other Customer [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	27.8	23.8	20.9
Gas [Member] | Other Customer [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	16.5	12.5	12.1
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenues	48.0	47.5	48.6
Other Utility [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	45.0	45.4	46.7
Other Utility [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	3.0	2.1	1.9
Other Utility [Member] | Other Customer [Member]
Disaggregation of Revenue [Line Items]
Revenues	12.8	12.9	14.7
Other Utility [Member] | Other Customer [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	9.8	10.8	12.8
Other Utility [Member] | Other Customer [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	3.0	2.1	1.9
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenues	35.2	34.6	33.9
Other Utility [Member] | Steam [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	35.2	34.6	33.9
Other Segments [Member]
Disaggregation of Revenue [Line Items]
Revenues	39.6	39.1	40.5
Other Segments [Member] | Other Customer [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 39.6	$ 39.1	$ 40.5