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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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