Benefit Plans (Allocation Of Pension Costs) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
IPL [Member]
Pension costs	$ 1.3	$ 1.5	$ 2.5	$ 3.0
WPL [Member]
Pension costs	$ 0.8	$ 1.0	$ 1.5	$ 1.8