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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions | 6 Months Ended
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Jun. 30, 2023 USD ($)
Coal Combustion Residuals [Member] | Minnesota Power [Member] |
Environmental Matters [Line Items] |
Expected Period for Costs of Compliance | 12 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) | $ 9

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