Disaggregation of Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 3,647.7	$ 3,534.5	$ 3,382.2
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,089.6	2,042.3	1,870.3
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,475.7	1,452.6	1,472.8
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,063.6	3,000.3	2,894.7
Electric [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,781.2	1,731.1	1,598.9
Electric [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,282.4	1,269.2	1,295.8
Electric [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,092.4	1,063.4	1,006.2
Electric [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	601.5	590.6	535.6
Electric [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	490.9	472.8	470.6
Electric [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	769.7	735.6	710.3
Electric [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	510.3	486.8	452.7
Electric [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	259.4	248.8	257.6
Electric [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	889.1	888.8	853.1
Electric [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	503.9	500.8	459.7
Electric [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	385.2	388.0	393.4
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenues	176.4	188.4	238.4
Electric [Member] | Wholesale [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	63.5	71.2	95.5
Electric [Member] | Wholesale [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	112.9	117.2	142.9
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	136.0	124.1	86.7
Electric [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	102.0	81.7	55.4
Electric [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	34.0	42.4	31.3
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues	455.2	446.6	400.9
Gas [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	264.2	266.2	226.0
Gas [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	191.0	180.4	174.9
Gas [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	259.4	254.4	224.7
Gas [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	149.3	152.3	123.2
Gas [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	110.1	102.1	101.5
Gas [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	133.0	133.0	123.2
Gas [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	74.9	75.9	67.9
Gas [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	58.1	57.1	55.3
Gas [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	16.0	14.9	16.7
Gas [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	11.7	10.2	11.1
Gas [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	4.3	4.7	5.6
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	46.8	44.3	36.3
Gas [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	28.3	27.8	23.8
Gas [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	18.5	16.5	12.5
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenues	46.5	48.0	47.5
Other Utility [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	44.2	45.0	45.4
Other Utility [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	2.3	3.0	2.1
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	9.3	12.8	12.9
Other Utility [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	7.0	9.8	10.8
Other Utility [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	2.3	3.0	2.1
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenues	37.2	35.2	34.6
Other Utility [Member] | Steam [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	37.2	35.2	34.6
Non-Utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	82.4	39.6	39.1
Non-Utility and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 82.4	$ 39.6	$ 39.1