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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($)
Coal Combustion Residuals [Member] | Minnesota Power [Member]
Environmental Matters [Line Items]
Expected Period for Costs of Compliance	15 years
Coal Combustion Residuals [Member] | Minimum [Member] | Minnesota Power [Member]
Environmental Matters [Line Items]
Estimated Costs of Compliance	$ 65
Coal Combustion Residuals [Member] | Maximum [Member] | Minnesota Power [Member]
Environmental Matters [Line Items]
Estimated Costs of Compliance	120
Manufactured Gas Plant [Member] | SWL&P [Member] | Superior, WI [Member]
Environmental Matters [Line Items]
Estimated Costs of Compliance (Accrued)	$ 15

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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