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Commitments, Guarantees and Contingencies - North Dakota Wind Development (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011
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North Dakota Wind Development [Line Items] |  |
Capital Cost Spent to Date | $ 33.5 | $ 27.8
Bison 1 Wind Project [Member] |  |
North Dakota Wind Development [Line Items] |  |
Number of Phases | 2 |
Generating Unit Capacity (MW) | 82 |
Transmission Line Capacity (kV) | 230 |
Total Project Cost | 173.8 |
Transmission Line Length (Miles) | 22 |
MPUC, Updated Rates, Order Date | November 3, 2011 |
Bison 1 Wind Project, Land Restoration and Upgrades [Member] |  |
North Dakota Wind Development [Line Items] |  |
Expected Capital Cost | 3.6 |
Capital Cost Spent to Date | 2.6 |
Bison 1 Wind Project, Phase 1 [Member] |  |
North Dakota Wind Development [Line Items] |  |
Project Completion Date | 2010 |
Bison 1 Wind Project, Phase 2 [Member] |  |
North Dakota Wind Development [Line Items] |  |
Project Completion Date | January 2012 |
Bison 2 Wind Project [Member] |  |
North Dakota Wind Development [Line Items] |  |
Capital Cost Spent to Date | 40.3 |
MPUC, Project, Approval Date | September 2011 |
NDPSC, Site Permit, Approval Date | August 2011 |
Bison 3 Wind Project [Member] |  |
North Dakota Wind Development [Line Items] |  |
Capital Cost Spent to Date | 25.8 |
MPUC, Project, Approval Date | November 2011 |
NDPSC, Site Permit, Approval Date | October 2011 |
Bison 2 and 3 Wind Projects, Each [Member] |  |
North Dakota Wind Development [Line Items] |  |
Generating Unit Capacity (MW) | 105 |
Project Completion Date | 2012 |
Expected Capital Cost | $ 160.0 |
DC Transmission Line from Square Butte [Member] |  |
North Dakota Wind Development [Line Items] |  |
Transmission Line Capacity (kV) | 250 |
Transmission Line Length (Miles) | 465 |

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- Details
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