Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 915.7	$ 987.2
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	730.3	743.4
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	266.8	274.7
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	182.3	181.1
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	209.9	208.7
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	40.9	46.5
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30.4	32.4
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	152.2	215.8
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90.5	131.8
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	45.7	63.6
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4.2	5.4
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.8	15.0
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.6	11.1
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10.0	8.4
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.6	2.7
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21.6	16.9
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21.6	16.9
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	518.9	555.1
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	424.8	419.8
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	147.4	147.5
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	119.7	116.6
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	121.2	116.1
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14.4	16.9
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22.1	22.7
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	83.0	124.6
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48.8	77.9
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24.1	34.8
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.3	3.2
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7.8	8.7
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.1	10.7
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10.0	8.4
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.1	2.3
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	375.2	415.2
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	305.5	323.6
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	119.4	127.2
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62.6	64.5
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	88.7	92.6
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26.5	29.6
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.3	9.7
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69.2	91.2
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	41.7	53.9
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21.6	28.8
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.9	2.2
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4.0	6.3
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.5	0.4
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0.5	$ 0.4