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

The percentage rate used to calculate dividend payments on preferred stock.

No definition available.

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration