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Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 MW | Dec. 31, 2011 | Dec. 31, 2010
Square Butte PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Unit Capacity (MW) | 455 |  |
Output Entitlement | 50.00% |  |
PPA Counterparty Debt Outstanding | $ 416.9 |  |
Annual Debt Service | 44 |  |
Power Purchased under Long-term Contracts | 67.1 | 61.2 | 55.2
Interest Expense | 11.1 | 11.1 | 10.2
Minnkota PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MW) | 50 |  |
Oliver Wind I PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MW) | 50 |  |
Term of Contract (Years) | 25 |  |
Fixed Capacity Charges | 0 |  |
Oliver Wind II PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MW) | 48 |  |
Term of Contract (Years) | 25 |  |
Fixed Capacity Charges | $ 0 |  |
Manitoba Hydro PPA (expires April 2015) [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MW) | 50 |  |
Manitoba Hydro PPA (expires April 2022) [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MWh) | 1,000,000 |  |
Manitoba Hydro PPA (expires 2035) [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Being Purchased (MW) | 250 |  |
Term of Contract (Years) | 15 |  |
Transmission Line Capacity (kV) | 500 |  |

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- Definition Long-Term Contract for Purchase of Electric Power, Fixed Capacity Carges + References No definition available. + Details
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- Definition The generating capacity of a production plant constructed and financed by a public utility district, cooperative, or other organization with whom exists a long-term contract to purchase electric power. + References No definition available. + Details
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- Definition Share of plant output being purchased in megawatts under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References No definition available. + Details
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- Definition Share of plant output being purchased in megawatthours under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References No definition available. + Details
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- Definition Term in years of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References No definition available. + Details
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- Definition Capacity of a transmission line in kilovolts. + References No definition available. + Details
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- Definition Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.D) -URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section D + Details
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- Definition Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service. If the utility is obligated to pay certain minimum amounts which cover debt service requirements whether or not the plant is operating, the amount can be disclosed here. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.D) -URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section D + Details
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- Definition The allocable portion of interest included in charges under a long-term contract to purchase electric power. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.D) -URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section D + Details
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- Details
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- Definition Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.D) -URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section D + Details
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- Definition The amount of purchased power procured under arrangements extending beyond one year or the normal operating cycle, if longer, which was charged against earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(b)) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.D) -URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030 + Details
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