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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions | 12 Months Ended
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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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