Leases (Schedule Of Lease Expenses Included In Consolidated Statements Of Income) (Details) (WPL [Member], Sheboygan Falls Energy Facility [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
WPL [Member] | Sheboygan Falls Energy Facility [Member]
Property, Plant and Equipment [Line Items]
Interest expense	$ 11.3	$ 11.7	$ 12.0
Depreciation and amortization	6.2	6.2	6.2
Total lease expenses included in Consolidated Statements of Income	$ 17.5	$ 17.9	$ 18.2