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Commitments and Contingencies (Details) $ in Millions |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Oct. 01, 2021 USD ($) | Aug. 18, 2017 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2024 USD ($) laborUnion MW | Dec. 31, 2013 USD ($)
Labor Commitments [Abstract] |  |  |  |  |
Percentage of total work force in union |  |  |  | 59.00% |
Percentage of Grundartangi work force represented by the labor unions |  |  |  | 86.00% |
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | laborUnion |  |  |  | 5 |
Percentage of domestic based work force represented by a union |  |  |  | 39.00% |
Percentage of foreign work force represented by union |  |  |  | 0.61 |
Contingent consideration, accrued interest and principal |  |  |  | $ 32.3 |
E.ON Contingent Obligation | Long-term Debt |  |  |  |  |
Labor Commitments [Abstract] |  |  |  |  |
Stated interest rate, percentage |  |  |  | 10.94% |
Netherlands |  |  |  |  |
Labor Commitments [Abstract] |  |  |  |  |
Percentage of total work force in union |  |  |  | 100.00% |
Pension Benefit Guarantee Corporation |  |  |  |  |
PBGC Settlement [Abstract] |  |  |  |  |
Required pension contributions above minimum |  |  |  |  | $ 17.4
Pension contributions, amended term, annual contribution | $ 2.4 |  |  |  |
Pension contributions, amended term, total contribution | $ 9.6 |  |  | $ 7.2 |
Pension contributions, term | 4 years |  |  |  |
Kenergy | Century Marketer, LLC |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Extension term |  |  |  | 1 year |
Required termination period |  |  |  | 1 year |
Hawesville | Kenergy |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Extension term |  |  |  | 1 year |
Required termination period |  |  |  | 1 year |
Sebree | Kenergy |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Extension term |  |  |  | 1 year |
Required termination period |  |  |  | 1 year |
Santee Cooper |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power agreement, power supply, percentage |  |  |  | 100.00% |
Grundartangi - HS, Landsvirkjun |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power currently available under the power purchase agreement, available (in megawatts) | MW |  |  |  | 545 |
Grundartangi - Landsvirkjun |  |  |  |  |
Power Contingencies [Abstract] |  |  |  |  |
Power currently available under the power purchase agreement, available (in megawatts) | MW |  |  |  | 25 |
Ravenswood Retiree Medical Benefits Changes |  |  |  |  |
Ravenswood litigation [Abstract] |  |  |  |  |
Litigation settlement amount |  | $ 23.0 |  |  |
Ravenswood litigation settlement installment period |  | 10 years |  |  |
Litigation payment to trust |  |  | $ 5.0 |  |
Gain (loss) related to litigation settlement |  |  | 5.5 |  |
Loss contingency accrual |  |  | $ 12.5 |  |
Litigation settlement, annual installment |  |  |  | $ 2.0 |
Litigation settlement installment period |  |  |  | 9 years |
Other current liabilities |  |  |  | $ 2.0 |
Other liabilities |  |  |  | $ 1.6 |

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