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%