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Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2017 USD ($) MW | Jun. 30, 2016 USD ($) | Jul. 28, 2017 MW
Square Butte [Member] | Square Butte PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
PPA Counterparty Total Debt Outstanding | $ | $ 311.6 |  |
Cost of Power Purchased | $ | 40.7 | $ 37.7 |
Pro Rata Share of PPA Counterparty Interest Expense | $ | $ 4.7 | $ 4.8 |
Square Butte [Member] | Square Butte PPA [Member] | Square Butte Coal-fired Unit [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity (MW) | 455 |  |
Output Entitlement | 50.00% |  |
Minnkota Power [Member] | Square Butte Coal-fired Unit [Member] | Minnkota Power PSA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output Entitlement | 28.00% | 28.00% |
Tenaska [Member] | Tenaska PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Contract Term (Years) | 20 years |  |
Wind Turbine Generators [Member] | Tenaska [Member] | Tenaska PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity (MW) | 250 |  |
Subsequent Event [Member] | Integrated Resource Plan [Member] | MPUC [Member] | Minimum [Member] | Natural Gas-Fired [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity (MW) |  |  | 525
Subsequent Event [Member] | Integrated Resource Plan [Member] | MPUC [Member] | Maximum [Member] | Natural Gas-Fired [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity (MW) |  |  | 550

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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 + 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 + Details
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