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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions | 9 Months Ended
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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

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