Benefit Plans (Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts ) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Carrying value	$ 20.5	$ 20.5
IPL [Member]
Carrying value	$ 5.0	$ 5.2