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Regulatory Matters - Integrated Resource Plan (Details) - MW | Jul. 28, 2017 | Jun. 30, 2017 | Dec. 31, 2015
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Wind Turbine Generators [Member] | Tenaska PPA [Member] | Tenaska [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) |  | 250 |
MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Natural Gas-Fired [Member] | Minimum [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) |  |  | 200
MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Natural Gas-Fired [Member] | Maximum [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) |  |  | 300
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Natural Gas-Fired [Member] | Minimum [Member] | Natural Gas PPA [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) | 525 |  |
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Natural Gas-Fired [Member] | Maximum [Member] | Natural Gas PPA [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) | 550 |  |
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Natural Gas PPA [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Output Being Purchased (MW) | 250 |  |
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Natural Gas-Fired [Member] | Natural Gas PPA [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Output Entitlement | 50.00% |  |
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Wind Turbine Generators [Member] | Tenaska PPA [Member] | Tenaska [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) | 250 |  |
Subsequent Event [Member] | MPUC [Member] | Integrated Resource Plan [Member] | Minnesota Power [Member] | Solar Energy Generation [Member] | Solar Energy PPA [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Generating Capacity (MW) | 10 |  |

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