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EQUITY INVESTMENTS - Narrative (Details) $ in Millions |  | 9 Months Ended
--- | --- | ---
Oct. 17, 2024 | Sep. 30, 2024 USD ($) MW
Wind Turbine Generators | Tenaska | Tenaska PPA | Minnesota Power |  |
Investments In ATC [Roll Forward] |  |
Generating capacity counterparty owned (MegaWatt) | MW |  | 250
Long-term contract for purchase of electric power |  | 20 years
ATC |  |
Investments In ATC [Roll Forward] |  |
Ownership percentage |  | 8.00%
Authorized return on equity |  | 10.02%
Authorized return on equity, including incentive adder |  | 10.52%
Basis point incentive adder |  | 0.50%
Approximate annual reduction in pretax income for FERC proposal to limit incentive adder, Allete's proportionate share | $ |  | $ 1
ATC | Subsequent Event |  |
Investments In ATC [Roll Forward] |  |
Authorized return on equity | 9.98% |
Authorized return on equity, including incentive adder | 10.48% |
Nobles 2 |  |
Investments In ATC [Roll Forward] |  |
Ownership percentage |  | 49.00%

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