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Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | $ 24.8 | $ 27.1 | $ 11.2 | |||||
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IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 12.5 | 12.3 | 7.7 | |||||
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WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 12.3 | 14.8 | 3.5 | |||||
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Whispering Willow - East Wind Project [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 12.5 | 12.3 | 7.7 | |||||
|
Whispering Willow - East Wind Project [Member] | IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 12.5 | 12.3 | 7.7 | |||||
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Whispering Willow - East Wind Project [Member] | WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 0 | 0 | 0 | |||||
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Bent Tree - Phase I Wind Project [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 9.3 | [1] | 9.3 | [1] | 1.2 | [1] | ||
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Bent Tree - Phase I Wind Project [Member] | IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 0 | [1] | 0 | [1] | 0 | [1] | ||
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Bent Tree - Phase I Wind Project [Member] | WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 9.3 | [1] | 9.3 | [1] | 1.2 | [1] | ||
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Cedar Ridge Wind Project [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 4.0 | 4.5 | 3.3 | |||||
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Cedar Ridge Wind Project [Member] | IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 0 | 0 | 0 | |||||
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Cedar Ridge Wind Project [Member] | WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 4.0 | 4.5 | 3.3 | |||||
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Subtotal [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 25.8 | 26.1 | 12.2 | |||||
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Subtotal [Member] | IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 12.5 | 12.3 | 7.7 | |||||
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Subtotal [Member] | WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 13.3 | 13.8 | 4.5 | |||||
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Deferral [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | (1.0) | [1] | 1.0 | [1] | (1.0) | [1] | ||
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Deferral [Member] | IPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | 0 | [1] | 0 | [1] | 0 | [1] | ||
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Deferral [Member] | WPL [Member]
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| Production Tax Credits [Line Items] | ||||||||
| Production tax credits, net of state tax impacts | $ (1.0) | [1] | $ 1.0 | [1] | $ (1.0) | [1] | ||
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