Benefit Plans (Schedule Of Qualified And Non-Qualified Pension And Other Post Retirement Benefits Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits Costs (Credits) [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan pension benefits costs (credits)	$ 0.5	$ 0.4
Pension Benefits Costs (Credits) [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan pension benefits costs (credits)	0.3	0.3
Other Postretirement Benefits Costs [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan pension benefits costs (credits)		0.4
Other Postretirement Benefits Costs [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan pension benefits costs (credits)		$ 0.2