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Acquisition of Jamalco - Narrative (Details) - USD ($) |  | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
May 02, 2023 | Jun. 30, 2024 | Mar. 31, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | Dec. 31, 2023
Business Acquisition [Line Items] |  |  |  |  |  |  |
Bargain purchase gain |  | $ 0 |  | $ 0 | $ 245,900,000 | $ 0 |
General Alumina Holdings Limited |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Payments to acquire business | $ 1.00 |  |  |  |  |  |
Bargain purchase gain |  |  | $ 245,900,000 |  | $ 245,900,000 |  | $ 273,400,000
Property, plant and equipment reduction |  |  | 29,000,000 |  |  |  |
Purchase, gain reduction |  |  | $ 29,000,000 |  |  |  |
Jamalco | General Alumina Holdings Limited |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Noncontrolling interest, ownership percentage by parent | 55.00% |  |  |  |  |  |
Jamalco | Clarendon Alumina Production Limited |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Ownership percentage by noncontrolling owners | 45.00% |  |  |  |  |  |

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