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Commitments, Guarantees and Contingencies - Capacity and Energy Table (Details) - MW | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Manitoba Hydro | Minnesota Power | Manitoba Hydro PPA (Expires 2040) |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric energy (MW) | 133 |  |
Manitoba Hydro | Minnesota Power | Manitoba Hydro PPA (Expires May 2035) |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric energy and capacity (MW) | 250 |  |
Tenaska | Minnesota Power | Nobles 2 |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric energy and capacity (MW) | 250 |  |
Oliver Wind | Minnesota Power | Oliver Wind I PPA |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric energy (MW) | 50 |  |
Oliver Wind | Minnesota Power | Oliver Wind II PPA |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric energy (MW) | 48 |  |
Basin | Minnesota Power | Basin Power Sales Agreement (Expires May 2028) |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being sold electric - capacity (MW) | 100 |  |
Great River Energy | Minnesota Power | Great River Energy Power Sales Agreement (Expires May 2025) |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being sold electric - capacity (MW) | 100 |  |
Oconto Electric Cooperative | Minnesota Power | Oconto Electric Cooperative Power Sales Agreement |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being sold electric - energy and capacity (MW) | 25 |  |
Basin Electric Power Cooperative | Minnesota Power | Basin Electric Cooperative PSA June 2022 - May 2023 |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being sold electric - capacity (MW) | 75 |  |
Basin Electric Power Cooperative | Minnesota Power | Basin Electric Cooperative PSA June 2023 - May 2025 |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being sold electric - capacity (MW) | 125 |  |
Square Butte | Minnesota Power | Square Butte PPA | Square Butte Coal-fired Unit |  |  |
Power Purchase Agreements [Line Items] |  |  |
Expected output entitlement | 50.00% |  |
Minnkota Power | Square Butte PPA | Minnkota Sales Agreement | Square Butte Coal-fired Unit |  |  |
Power Purchase Agreements [Line Items] |  |  |
Expected output entitlement | 37.00% | 32.00% | 28.00%
Silver Bay Power | Minnesota Power | Silver Bay Power Self-Generation |  |  |
Power Purchase Agreements [Line Items] |  |  |
Energy generation owned (MW) | 90 |  |
Calpine Corporation PPA | Calpine Corporation | Minnesota Power |  |  |
Power Purchase Agreements [Line Items] |  |  |
Output being purchased - electric capacity (MW) | 25 |  |

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