Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Coal Combustion Residuals | Minnesota Power
Environmental Matters [Line Items]
Expected period for costs of compliance	12 years
Coal Combustion Residuals | Minimum | Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance	$ 65
Coal Combustion Residuals | Maximum | Minnesota Power
Environmental Matters [Line Items]
Estimated costs of compliance	120
Manufactured Gas Plant | SWL&P | Superior, WI
Environmental Matters [Line Items]
Redemption cost liability	$ 4