Property, Plant and Equipment (AFUDC By Project) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 30.8	$ 21.9	$ 12.0
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	21.0	8.4	5.8
IPL [Member] | Ottumwa Unit 1 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	8.0	2.0	0
IPL [Member] | George Neal Units 3 and 4 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	5.1	0.9	0
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.9	5.5	5.8
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	9.8	13.5	6.2
WPL [Member] | Columbia Units 1-2 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.2	3.9	0.2
WPL [Member] | Edgewater Unit 5 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0	7.2	2.9
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 2.6	$ 2.4	$ 3.1