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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 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]
Environmental remediation liability	$ 1

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