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Commitments and Contingencies, Legal Contingencies (Details) (USD $)
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Sep. 30, 2012
Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]
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Feb. 29, 2008
Native Village of Kivalina vs. Xcel Energy Inc. et al. [Member]
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Sep. 30, 2012
Comer vs. Xcel Energy Inc. et al. [Member]
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May 31, 2011
Comer vs. Xcel Energy Inc. et al. [Member]
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Sep. 30, 2012
Exelon Wind Complaint [Member]
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| Legal Contingencies [Abstract] | |||||
| Number of other entities against which the native village of Kivalina has filed a lawsuit | 23 | ||||
| Estimated cost of relocating the village of Kivalina, low end of range | $ 95,000,000 | ||||
| Estimated cost of relocating the village of Kivalina, high end of range | 400,000,000 | ||||
| Accrual for legal contingency | $ 0 | $ 0 | $ 0 | ||
| Minimum number of utility, oil, chemical and coal companies against which a lawsuit was filed in U.S. District Court in Mississippi | 85 | ||||
| Number of main areas of dispute | 2 | ||||
| Number of wind facilities | 12 |