Benefit Plans (Schedule Of Qualified and Non-qualified Pension And Other Postretirement Benefits Costs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Defined benefit pension plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	$ 0.5	$ 0.5
Defined benefit pension plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	0.3	0.3
Other Postretirement Benefits Costs [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	(0.1)	0
Other Postretirement Benefits Costs [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	$ 0	$ 0