Summary Of Significant Accounting Policies (Schedule Of Amortization Expense on Emissions Allowance) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0	$ 13.4	$ 16.5
IPL [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	0	12.9	13.1
WPL [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0	$ 0.5	$ 3.4