Benefit Plans (Schedule Of Qualified and Non-qualified Pension And Other Postretirement Benefits Costs (Credits)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined benefit pension plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs (credits) associated with Corporate Services employees	$ 0.4	$ 0.4	$ 1.4	$ 1.4
Defined benefit pension plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs (credits) associated with Corporate Services employees	0.4	0.4	1.1	1.0
Other Postretirement Benefits Costs (Credits) [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs (credits) associated with Corporate Services employees	(0.1)	0	(0.2)	0.1
Other Postretirement Benefits Costs (Credits) [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs (credits) associated with Corporate Services employees	$ (0.1)	$ 0.1	$ (0.2)	$ 0.1