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Investments (Unconsolidated Equity Investments) (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|
|
Dec. 31, 2012
|
Dec. 31, 2011
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Dec. 31, 2010
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Carrying value | $ 266.6 | $ 249.6 | $ 238.5 | |||||
| Equity (income) / loss | (41.3) | (39.3) | (38.1) | |||||
|
WPL [Member]
|
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Equity (income) / loss | (42.1) | (38.7) | (37.8) | |||||
|
American Transmission Company LLC (ATC) [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Ownership interest | 16.00% | [1] | ||||||
| Carrying value | 257.0 | [1] | 238.8 | [1] | ||||
| Equity (income) / loss | (41.3) | [1] | (37.8) | [1] | (36.9) | [1] | ||
|
American Transmission Company LLC (ATC) [Member] | WPL [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Ownership interest | 16.00% | [1] | ||||||
| Carrying value | 257.0 | [1] | 238.8 | [1] | ||||
| Equity (income) / loss | (41.3) | [1] | (37.8) | [1] | (36.9) | [1] | ||
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Wisconsin River Power Company [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Ownership interest | 50.00% | |||||||
| Carrying value | 7.3 | 7.7 | ||||||
| Equity (income) / loss | (0.8) | (0.9) | (0.9) | |||||
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Wisconsin River Power Company [Member] | WPL [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Ownership interest | 50.00% | |||||||
| Carrying value | 7.3 | 7.7 | ||||||
| Equity (income) / loss | (0.8) | (0.9) | (0.9) | |||||
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Other Equity [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Carrying value | 2.3 | 3.1 | ||||||
| Equity (income) / loss | 0.8 | (0.6) | (0.3) | |||||
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Totals [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Carrying value | 266.6 | 249.6 | ||||||
| Equity (income) / loss | (41.3) | (39.3) | (38.1) | |||||
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Totals [Member] | WPL [Member]
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| Schedule of Equity Method Investments [Line Items] | ||||||||
| Carrying value | 264.3 | 246.5 | ||||||
| Equity (income) / loss | $ (42.1) | $ (38.7) | $ (37.8) | |||||
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