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Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 USD ($) MW | Sep. 30, 2016 USD ($) | Jul. 28, 2017 MW
Square Butte [Member] | Square Butte PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
PPA Counterparty Total Debt Outstanding | $ | $ 309.3 |  |
Cost of Power Purchased | $ | 60.6 | $ 56.8 |
Pro Rata Share of PPA Counterparty Interest Expense | $ | $ 7.1 | $ 7.2 |
Square Butte [Member] | Square Butte PPA [Member] | Coal-fired Generation [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity to be Counterparty Owned (MW) | 455 |  |
Expected Output Entitlement | 50.00% |  |
Minnkota Power [Member] | Coal-fired Generation [Member] | Minnkota Power PSA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Expected Output Entitlement | 28.00% | 28.00% |
Tenaska [Member] | Tenaska PPA [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Contract Term (Years) | 20 years |  |
Tenaska [Member] | Tenaska PPA [Member] | Wind Turbine Generators [Member] | Resource Package [Member] | MPUC [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity to be Counterparty Owned (MW) | 250 |  |
Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Natural Gas-fired [Member] | Resource Package [Member] | MPUC [Member] | Combined-Cycle Natural Gas-fired Generating Facility [Member] | Jointly Owned Electricity Generation Plant [Member] | Minimum [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity to be Jointly Owned (MW) | 525 |  | 525
Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Natural Gas-fired [Member] | Resource Package [Member] | MPUC [Member] | Combined-Cycle Natural Gas-fired Generating Facility [Member] | Jointly Owned Electricity Generation Plant [Member] | Maximum [Member] |  |  |
Power Purchase Agreements [Line Items] |  |  |
Generating Capacity to be Jointly Owned (MW) | 550 |  | 550

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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 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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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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