COMMITMENTS, GUARANTEES AND CONTINGENCIES - Environmental Matters (Details) $ in Millions		6 Months Ended
	May 08, 2024 USD ($)	Jun. 30, 2024 USD ($)	Sep. 29, 2023 state	Jun. 05, 2023 state
Environmental Matters [Line Items]
Number of states contributed to downwind states’ challenges in attaining or maintaining ozone NAAQS				23
Number of states restrictions on fossil-fuel fired power plants				22
Number of states restricted on certain industrial sources				20
States were EPA issued an updated final interim rule addressing the stays			5
Coal Combustion Residuals | Minnesota Power
Environmental Matters [Line Items]
Expected period for costs of compliance	10 years	12 years
Coal Combustion Residuals | Minimum | Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance | $	$ 50	$ 65
Coal Combustion Residuals | Maximum | Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance | $	$ 85	120
Manufactured Gas Plant | SWL&P | Superior, WI
Environmental Matters [Line Items]
Redemption cost liability | $		$ 1