Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 62.5	$ 36.9	$ 34.8
Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	42.3	24.4	23.1
Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	20.2	12.5	11.7
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	52.0	28.2	25.9
IPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	35.2	18.6	17.1
IPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	16.8	9.6	8.8
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	10.5	8.7	8.9
WPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.1	5.8	6.0
WPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 3.4	$ 2.9	$ 2.9