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Curtailment of Operations - Hawesville (Details) - Curtailment Of Operations - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Restructuring Cost and Reserve [Line Items]    
Severance costs $ 0.6 $ 7.0
Gain (loss) on material sales $ 0.5 0.7
Temporary Facility Closing, Excess Capacity    
Restructuring Cost and Reserve [Line Items]    
Excess capacity charges   $ 5.4