Property, Plant and Equipment (AFUDC By Project) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 36.9	$ 34.8	$ 30.8
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	28.2	25.9	21.0
IPL [Member] | Marshalltown Generating Station [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	20.7	3.7	0.0
IPL [Member] | Ottumwa Unit 1 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0.0	10.6	8.0
IPL [Member] | George Neal Units 3 and 4 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0.0	1.4	5.1
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.5	10.2	7.9
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	8.7	8.9	9.8
WPL [Member] | Edgewater Unit 5 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	5.1	2.7	0.0
WPL [Member] | Columbia Units 1 and 2 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0.0	4.0	7.2
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 3.6	$ 2.2	$ 2.6