General	3 Months Ended
General	Mar. 31, 2020
Accounting Policies [Abstract]
General	General The accompanying unaudited interim consolidated financial statements of Century Aluminum Company should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2019. In management’s opinion, the unaudited interim consolidated financial statements reflect all adjustments, which are of a normal and recurring nature, that are necessary for a fair presentation of financial results for the interim periods presented. Operating results for the first three months of 2020 are not necessarily indicative of the results that may be expected for the year ending December 31, 2020. Throughout this Form 10-Q, and unless expressly stated otherwise or as the context otherwise requires, "Century Aluminum," "Century," the "Company," "we," "us," "our" and "ours" refer to Century Aluminum Company and its consolidated subsidiaries. Recently Adopted Accounting Standards On January 1, 2020, we adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2016-13, “Measurement of Credit Losses on Financial Instruments.” The ASU added an impairment model known as the current expected credit loss ("CECL") model, which is based on expected losses rather than incurred losses. The CECL model is applicable to our receivables, both from related parties and third-party customers related to the sale of primary aluminum (collectively, “trade receivables”). We do not have any other financial instruments or assets to which the CECL model applies. The adoption of the CECL model did not have a material impact on the Company’s consolidated financial statements. On January 1, 2020, we adopted FASB ASU 2018-13, “Disclosure Framework- Changes to the Disclosure Requirements for Fair Value Measurement” which changed the fair value measurement disclosure requirements of ASC 820. The additional disclosures include a requirement to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. The new framework also eliminates and modifies certain other fair value disclosures. See Note 4. Fair Value Measurement for updated fair value disclosures in connection with the adoption of this accounting standard. Recently Issued Accounting Standards In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." Amendments include the removal of certain exceptions to the general principles of ASC 740 and to improve and simplify accounting for income taxes by clarifying and amending existing guidance. Updates are related to intraperiod tax allocation, interim period tax calculations, tax laws or rate changes in interim periods, and income taxes related to employee stock ownership plans. The ASU is effective for fiscal years beginning after December 15, 2020, including interim periods therein and early adoption is permitted. The Company is currently evaluating the impacts of ASU 2019-12 and we do not expect the adoption to have a material effect on the consolidated financial statements. In March 2020, the Securities and Exchange Commission (“SEC”) issued a final rule that amends the disclosure requirements related to certain registered securities under SEC Regulation S-X Rule 3-10 with respect to the disclosure requirements related to issuers and guarantors of guaranteed debt securities. The final rule allows registrants to provide alternative financial disclosures in either the registrant’s MD&A or financial statements, rather than the previous requirement under Rule 3-10, which required condensed consolidating financial information within the financial statements. It also simplifies the requirements in Rule 3-10 that currently must be met for a parent company to qualify for exceptions allowing it to provide alternative disclosures rather than full audited financial statements. The ruling also reduces the periods for which summarized financial information is required to be presented to the most recent (1) annual period and (2) year-to-date interim period. The final rule applies to annual reports on Form 10-K for fiscal years ending after January 4, 2021 and quarterly reports on Form 10-Q for quarterly periods ending after January 4, 2021 and registrants may voluntarily comply with the final rule before the effective date. The Company does not expect the future adoption, which is limited to disclosures only, to have a material effect on the Company’s consolidated financial statements.