Fair Value Measurements (Narrative) (Details)	1 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Apr. 30, 2011	Jun. 30, 2011 IPL [Member]	Dec. 31, 2010 IPL [Member]	Jun. 30, 2011 WPL [Member]	Dec. 31, 2010 WPL [Member]
Cumulative preferred stock rate	7.10%	8.375%	7.10%	4.50%	4.50%