Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Production Tax Credits [Line Items]
Production Tax Credits	$ 4.6	$ 5.1	$ 22.0	$ 22.4
WPL [Member]
Production Tax Credits [Line Items]
Production Tax Credits	2.6	2.8	12.2	12.1
Cedar Ridge Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			68
Production Tax Credits	0.6	0.6	2.8	2.9
Bent Tree - Phase I Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			201
Production Tax Credits	2.0	2.2	9.4	9.2
Whispering Willow - East Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)			200
Production Tax Credits	$ 2.0	$ 2.3	$ 9.8	$ 10.3