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General (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Segment Reporting Information [Line Items] |  |  |  |
Bargain purchase gain | $ 0.0 | $ 0.0 | $ 0.0 | $ 245.9
General Alumina Holdings Limited |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Bargain purchase gain |  |  |  | $ 245.9
Bauxite Mining and Alumina Refinery Joint Venture |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Noncontrolling interest, ownership percentage by parent | 55.00% |  | 55.00% |

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