Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	$ 31.0	$ 24.8	$ 27.1
IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.4	12.5	12.3
WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	16.6	12.3	14.8
Whispering Willow - East Wind Project [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.4	12.5	12.3
Whispering Willow - East Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.4	12.5	12.3
Whispering Willow - East Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	0	0	0
Bent Tree - Phase I Wind Project [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	12.5	9.3	9.3
Bent Tree - Phase I Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	0	0	0
Bent Tree - Phase I Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	12.5	9.3	9.3
Cedar Ridge Wind Project [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	4.1	4.0	4.5
Cedar Ridge Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	0	0	0
Cedar Ridge Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	4.1	4.0	4.5
Subtotal [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	31.0	25.8	26.1
Subtotal [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.4	12.5	12.3
Subtotal [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	16.6	13.3	13.8
Deferral [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	0	(1.0)	1.0
Deferral [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	0	0	0
Deferral [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	$ 0	$ (1.0)	$ 1.0