Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Production Tax Credits [Line Items]
Production Tax Credits	$ 7.4	$ 8.7	$ 17.4	$ 17.3
WPL [Member]
Production Tax Credits [Line Items]
Production Tax Credits	4.2	4.6	9.6	9.3
Cedar Ridge Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			68
Production Tax Credits	1.0	1.1	2.2	2.3
Bent Tree - Phase I Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			201
Production Tax Credits	3.2	3.5	7.4	7.0
Whispering Willow - East Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			200
Production Tax Credits	$ 3.2	$ 4.1	$ 7.8	$ 8.0