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Related Party Transactions - Narrative (Details) carbon_credit in Thousands, € in Millions, $ in Millions			12 Months Ended
	Dec. 18, 2023 EUR (€) carbon_credit € / carbonCredit	Sep. 28, 2023 EUR (€) carbon_credit € / carbonCredit	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 09, 2022 USD ($)
Related Party Transaction [Line Items]
Net sales | $			$ 2,185.4	$ 2,777.3	$ 2,212.5
Supply Commitment | Glencore
Related Party Transaction [Line Items]
Net sales | $			$ 191.7	$ 24.9	$ 18.3
Century Aluminum | Glencore
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners			42.90%
Economic ownership percentage by related party			46.00%
Affiliated Entity | Vlissingen Facility Agreement | Vlissingen
Related Party Transaction [Line Items]
Credit facility face amount | $						$ 90.0
Stated interest rate						8.75%
Affiliated Entity | Carbon Credit Sale | Nordural Grundartangi ehf
Related Party Transaction [Line Items]
Carbon credit sold in transaction | carbon_credit	40	390
Sale price (Euro per carbon credit) | € / carbonCredit	69.30	82.18
Aggregate amount | €		€ 32.1
Affiliated Entity | Carbon Credit Repurchase | Nordural Grundartangi ehf
Related Party Transaction [Line Items]
Sale price (Euro per carbon credit) | € / carbonCredit	85.13	83.72
Aggregate amount | €	€ 33.2	€ 32.7
Affiliated Entity | Additional Carbon Credit Repurchase | Nordural Grundartangi ehf
Related Party Transaction [Line Items]
Sale price (Euro per carbon credit) | € / carbonCredit	70.71
Aggregate amount | €	€ 2.8
Customer Concentration Risk | Sales Revenue | Glencore
Related Party Transaction [Line Items]
Major customer, percentage revenue, net			73.80%	60.20%	60.00%

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