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				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Pension Benefits Costs [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	$ 0.5	[1]	$ 3.7	[1]	$ 1.0	[1]	$ 4.1	[1]
Pension Benefits Costs [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	0.3	[1]	2.7	[1]	0.6	[1]	3.0	[1]
Other Postretirement Benefits Costs [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	0.1		0		0.1		0.4
Other Postretirement Benefits Costs [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits costs associated with Corporate Services employees	$ 0		$ 0.1		$ 0		$ 0.3

[1] For both the three and six months ended June 30, 2011, additional qualified pension benefits costs resulting from the amendment to the Cash Balance Plan in the second quarter of 2011 allocated to IPL and WPL by Corporate Services were $3.3 million and $2.4 million, respectively.