Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 IPL [Member]	Dec. 31, 2012 IPL [Member]	Dec. 31, 2012 WPL [Member]	Dec. 31, 2013 Commodity Contracts [Member]	Dec. 31, 2012 Commodity Contracts [Member]	Dec. 31, 2011 Commodity Contracts [Member]	Dec. 31, 2013 Commodity Contracts [Member] IPL [Member]	Dec. 31, 2012 Commodity Contracts [Member] IPL [Member]	Dec. 31, 2011 Commodity Contracts [Member] IPL [Member]	Dec. 31, 2013 Commodity Contracts [Member] WPL [Member]	Dec. 31, 2012 Commodity Contracts [Member] WPL [Member]	Dec. 31, 2011 Commodity Contracts [Member] WPL [Member]	Dec. 31, 2013 Excluding FTRs [Member] Commodity Contracts [Member]	Dec. 31, 2013 Excluding FTRs [Member] Commodity Contracts [Member] IPL [Member]	Dec. 31, 2013 Excluding FTRs [Member] Commodity Contracts [Member] WPL [Member]	Dec. 31, 2013 FTRs [Member] Commodity Contracts [Member]	Dec. 31, 2013 FTRs [Member] Commodity Contracts [Member] IPL [Member]	Dec. 31, 2013 FTRs [Member] Commodity Contracts [Member] WPL [Member]
Cumulative preferred stock rate	5.10%	8.375%	4.50%
Fair value				$ 4.4	$ 11.9	$ (0.9)	$ 14.6	$ 12.5	$ 4.3	$ (10.2)	$ (0.6)	$ (5.2)	$ (13.9)	$ (2.1)	$ (11.8)	$ 18.3	$ 16.7	$ 1.6