| Document and Entity Information Document | Mar. 25, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 25, 2021 |
| Entity Registrant Name | Century Aluminum Company |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-34474 |
| Entity Tax Identification Number | 13-3070826 |
| Entity Address, Address Line One | One South Wacker Drive |
| Entity Address, Address Line Two | Suite 1000 |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60606 |
| City Area Code | (312) |
| Local Phone Number | 696-3101 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value per share |
| Trading Symbol | CENX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000949157 |
| Amendment Flag | false |
