Leases (Schedule Of Lease Expenses Included In Consolidated Statements Of Income) (Details) - WPL [Member] - Sheboygan Falls Energy Facility [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Interest expense	$ 8.7	$ 9.3	$ 9.9
Depreciation and amortization	6.2	6.2	6.2
Total lease expenses included in income statements	$ 14.9	$ 15.5	$ 16.1