Audit Information |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Audit Information [Abstract] | |
| Auditor Name | Deloitte & Touche LLP |
| Auditor Location | Chicago, Illinois |
| Auditor Firm ID | 34 |
CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
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| Net sales | ||||||||||||||
| Total net sales | $ 2,527.9 | $ 2,220.3 | $ 2,185.4 | |||||||||||
| Cost of Goods Sold | $ 557.3 | $ 594.5 | $ 576.6 | $ 462.2 | $ 545.3 | $ 476.5 | 2,271.5 | [1] | 2,048.3 | [1] | 2,097.8 | [1] | ||
| Gross profit | 74.9 | 33.6 | 57.3 | 76.9 | 15.5 | 13.0 | 256.4 | 172.0 | 87.6 | |||||
| Selling, general and administrative expenses | 79.9 | 56.8 | 44.3 | |||||||||||
| Other operating expenses - net | 18.4 | 6.8 | 15.8 | |||||||||||
| Operating income | 55.9 | 18.1 | 42.8 | 58.9 | 1.5 | (1.6) | 158.1 | 108.4 | 27.5 | |||||
| Interest income | 9.2 | 2.1 | 2.0 | |||||||||||
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.0 | 61.8 | |||||||||||
| Loss on early extinguishment of debt | (7.7) | 0.0 | 0.0 | |||||||||||
| Bargain purchase gain | 0.0 | 245.9 | 0.0 | |||||||||||
| Other expense - net | (14.5) | (5.5) | (3.3) | |||||||||||
| Income (loss) before income taxes | 7.1 | (13.0) | 24.0 | 39.4 | (11.1) | 241.7 | 2.7 | 309.8 | (71.1) | |||||
| Income tax benefit (expense) | 13.1 | (3.2) | 14.6 | |||||||||||
| Income (loss) before equity in earnings of joint ventures | 15.8 | 306.6 | (56.5) | |||||||||||
| Equity in earnings (losses) of joint ventures | 0.0 | 0.1 | (0.1) | |||||||||||
| Net income (loss) | 8.2 | (11.7) | 22.4 | 37.4 | (11.6) | 241.2 | 15.8 | 306.7 | (56.6) | |||||
| Net loss attributable to noncontrolling interests | (6.7) | (7.1) | (7.3) | (9.9) | (9.1) | (5.6) | (26.0) | (30.1) | (13.5) | |||||
| Net income (loss) attributable to Century stockholders | 14.9 | (4.6) | 29.7 | 47.3 | (2.5) | 246.8 | 41.8 | 336.8 | (43.1) | |||||
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 1.8 | 17.9 | 0.0 | |||||
| Net income (loss) allocated to common stockholders | $ 14.1 | $ (4.6) | $ 28.2 | $ 44.8 | $ (2.5) | $ 233.6 | $ 40.0 | $ 318.9 | $ (43.1) | |||||
| Net income (loss) attributable to Century stockholders per common share: | ||||||||||||||
| Basic (in dollars per share) | $ 0.42 | $ 3.44 | $ (0.47) | |||||||||||
| Diluted (in dollars per share) | $ 0.42 | $ 3.27 | $ (0.47) | |||||||||||
| Weighted-average common shares outstanding: | ||||||||||||||
| Basic (in shares) | 94.2 | 92.8 | 92.4 | |||||||||||
| Diluted (in shares) | 95.3 | 98.4 | 92.4 | |||||||||||
| Related Party | ||||||||||||||
| Net sales | ||||||||||||||
| Total net sales | $ 1,365.5 | $ 1,312.1 | $ 1,612.1 | |||||||||||
| Cost of Goods Sold | 294.0 | 277.9 | 181.4 | |||||||||||
| Interest expense | (5.8) | (6.7) | (1.8) | |||||||||||
| Net gain (loss) on forward and derivative contracts | 0.0 | (0.5) | 0.6 | |||||||||||
| Nonrelated Party | ||||||||||||||
| Net sales | ||||||||||||||
| Total net sales | 1,162.4 | 908.2 | 573.3 | |||||||||||
| Interest expense | (41.9) | (36.4) | (33.7) | |||||||||||
| Net gain (loss) on forward and derivative contracts | $ (94.7) | $ 2.5 | $ (62.4) | |||||||||||
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CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
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| Cost of Goods Sold | $ 557.3 | $ 594.5 | $ 576.6 | $ 462.2 | $ 545.3 | $ 476.5 | $ 2,271.5 | [1] | $ 2,048.3 | [1] | $ 2,097.8 | [1] | ||
| Related Party | ||||||||||||||
| Cost of Goods Sold | $ 294.0 | $ 277.9 | $ 181.4 | |||||||||||
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CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical) |
Dec. 31, 2025 |
Dec. 31, 2023 |
|---|---|---|
| Jamalco | ||
| Ownership percentage | 55.00% | 55.00% |
Summary of Significant Accounting Policies |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Accounting Policies [Abstract] | |
| Summary of Significant Accounting Policies | 1. Summary of Significant Accounting Policies Organization — Century Aluminum Company ("Century Aluminum," "Century," the "Company", "we", "us", "our" or "ours") is a holding company, whose principal subsidiaries are Nordural ehf (together with its subsidiaries, "Nordural"), Century Aluminum Sebree LLC ("Century Sebree"), Century Aluminum of South Carolina, Inc. ("CASC") and Century Kentucky, Inc. ("CAKY"). Nordural Grundartangi ehf, a subsidiary of Nordural, operates a primary aluminum smelter in Grundartangi, Iceland ("Grundartangi"). Century Sebree operates a primary aluminum smelter in Robards, Kentucky ("Sebree"). CASC operates a primary aluminum smelter in Goose Creek, South Carolina ("Mt. Holly"). CAKY owned a primary aluminum smelter in Hawesville, Kentucky ("Hawesville"), which was sold on February 2, 2026. See Note 24. Subsequent Events for additional information on the sale. In addition to our primary aluminum assets, we have a 55% joint venture interest in the Jamalco bauxite mining operation and alumina refinery in Jamaica ("Jamalco"). The Jamalco refinery supplies a substantial amount of the alumina used for production of primary aluminum at our aluminum smelter in Grundartangi, Iceland. Additionally, our subsidiary, Century Aluminum Vlissingen B.V., owns and operates a carbon anode production facility located in Vlissingen, the Netherlands ("Vlissingen"). Carbon anodes are used in the production of primary aluminum, and Vlissingen currently supplies carbon anodes to Grundartangi. As of December 31, 2025, Glencore owns 36.4% of Century’s outstanding common stock. Century and Glencore enter into various transactions from time to time such as the purchase and sale of primary aluminum, purchase and sale of alumina and raw materials, tolling agreements as well as forward financial contracts and borrowing and other debt transactions. See Note 4. Related Party Transactions. Basis of Presentation — The consolidated financial statements include the accounts of Century Aluminum Company and our subsidiaries, after elimination of all intercompany transactions and accounts. The consolidated financial statements are prepared in accordance with generally accepted accounting principles in the United States ("U.S. GAAP"). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Our consolidated financial statements include the consolidated results of the Jamalco joint venture, an unincorporated joint venture between General Alumina Jamaica Limited ("GAJL"), an indirect, wholly-owned subsidiary of the Company, and Clarendon Alumina Production Limited ("CAP"). CAP's interest in the joint venture is reflected as noncontrolling interest on the accompanying Consolidated Balance Sheet. Variable Interest Entities - We evaluate arrangements and contracts with other entities to determine if they are VIEs and if we are the primary beneficiary. U.S. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, non-controlling interest, and results of activities of a VIE in its consolidated financial statements. A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE’s most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE’s assets, liabilities, and non-controlling interests at fair value and subsequently account for the VIE as if it were consolidated. Our evaluation of whether our interest qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE’s economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement. Jamalco is a VIE. See Note 21. Variable Interest Entity. Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds and short-term investments having original maturities of three months or less. The carrying amount of cash equivalents approximates fair value. Accounts Receivable and Due from Affiliates — These amounts are net of an immaterial allowance for expected losses. Inventories — Our inventories are stated at the lower of cost or net realizable value, using the first-in, first-out ("FIFO") and the weighted average cost method. Due to the nature of our business, our inventory values are subject to market price changes and these changes can have a significant impact on Cost of goods sold and Gross profit in any period. Reductions in net realizable value below cost basis at the end of a period will have an impact on our Cost of goods sold as this inventory is sold in subsequent periods. Property, Plant and Equipment — Property, plant and equipment is stated at cost. Additions and improvements are capitalized when each asset is placed into service. Asset and accumulated depreciation accounts are relieved for dispositions with resulting gains or losses included in Other expense - net. Maintenance and repairs are expensed as incurred. Depreciation of plant and equipment is provided for by the straight-line method over the following estimated useful lives: Building and improvements 10 to 45 years Machinery and equipment 5 to 35 years Technology and software 3 to 7 years The Company incurs deferred costs during the development stage of a mine life cycle. Such costs include the construction of access and haul roads, detailed drilling and geological analysis to further define the grade and quality of the known bauxite, and overburden removal costs. These costs relate to sections of the related mines where the Company is currently extracting bauxite or preparing for production in the near term. These sections are outlined and planned incrementally and generally are mined over periods outlined in the Company's mine plans. The amount of geological drilling and testing necessary to determine the economic viability of the bauxite deposit being mined is such that the resources are considered to be proved mineral reserves. Mineral reserves are amortized on a units-of-production basis. Impairment of long-lived assets — The Company reviews property, plant and equipment and right of use assets ("long-lived assets") for impairment whenever events or changes in circumstances, known as triggering events, indicate that the carrying amount of a long-lived asset or an asset group may not be recoverable. Management considers various factors when determining if long-lived assets should be evaluated for impairment, including a significant adverse change in the business climate or industry conditions (such as sustained decreases in commodity prices, volatility in energy costs, and the global economy), a current period operating or cash flow loss combined with a history of losses, a significant adverse change in the extent or manner in which an asset is used or a current expectation that the asset will be sold or otherwise disposed of before the end of its useful life. If a triggering event is identified, the Company determines if the long-lived asset or asset group is recoverable. Recoverability is measured by comparison of the carrying amount of a long-lived asset or asset group held and used to estimate undiscounted future net cash flows expected to be generated by the long-lived asset or asset group. Impairment evaluation and fair value is based on estimates and assumptions that take into account our business plans and a long-term investment horizon, including consideration of commodity pricing, energy costs and other global economic conditions which may have an adverse effect on recoverability. If deemed unrecoverable, an impairment loss would be recognized for the amount by which the carrying amount exceeds the estimated fair value of the long-lived asset or asset group. Leases — We enter into operating lease contracts, as assessed at the inception of the arrangement, for real estate, automobiles, and mobile equipment. We use our incremental borrowing rate as the basis for the discount rate used to calculate the right of use asset ("ROUA") and lease liability. The incremental borrowing rate is determined on a lease-by-lease basis. The terms of our leases vary, including the lease term and the ability to renew or extend certain leases. As part of determining the lease term and potential extensions for purposes of calculating the ROUA and lease liability, we consider our historical practices related to renewal of certain leases. We have made a policy election not to separate lease and non-lease components within contracts. We have also elected not to recognize the impact of short term leases in the ROUA and lease liability balances. Short term leases are leases that have a lease term less than one year and do not include a purchase option. Income Taxes — We account for income taxes using the asset and liability method, whereby deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. In evaluating our ability to realize deferred tax assets, we use judgment to determine if it is more likely than not that some portion or all of a deferred tax asset will not be realized, and if a corresponding valuation allowance is required. Defined Benefit Pension and Other Postretirement Benefits — We sponsor defined benefit pension and Other Postretirement Benefit ("OPEB") plans for certain of our domestic hourly and salaried employees and a supplemental executive retirement benefit plan for certain current and former executive officers. Plan assets and obligations are measured annually or more frequently if there is a re-measurement event, based on the Company’s measurement date utilizing various actuarial assumptions. We attribute the service costs for the plans over the working lives of plan participants. The effects of actual results differing from our assumptions and the effects of changing assumptions are considered actuarial gains or losses. Actuarial gains or losses are recorded in Accumulated other comprehensive income (loss). Net periodic benefit cost is a component of Cost of goods sold; Selling, general and administrative expenses and Other expense - net. We contribute to our defined benefit pension plans based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements. Postemployment Benefits — We provide certain postemployment benefits to certain former and inactive employees and their dependents during the period following employment but before retirement. These benefits include salary continuance, supplemental unemployment and disability health care. We recognize the estimated future cost of providing postemployment benefits on an accrual basis over the active service life of the employee. Net periodic benefit cost is a component of Cost of goods sold; Selling, general and administrative expenses and Other expense - net. Derivatives and Hedging — As a global producer of primary aluminum, our operating results and cash flows from operations are subject to risk of fluctuations in the market prices of primary aluminum. We may from time to time enter into financial contracts to manage our exposure to such risk. Derivative instruments may consist of variable to fixed financial contracts and back-to-back fixed to floating arrangements for a portion of our sale of primary aluminum, where we receive fixed and pay floating prices from our customers and to counterparties, respectively. From time to time, we may manage our exposure to fluctuations in the market price of power through financial instruments designed to protect our downside risk exposure. We are also exposed to foreign currency risk, and we may manage our exposure by entering into foreign currency forward contracts or option contracts for forecasted transactions and projected cash flows for foreign currencies in future periods. Our derivatives are not designated as cash flow hedges. Derivative and hedging instruments are recorded in Derivative assets, Other assets, Derivative liabilities and Derivative liabilities - less current portion in the Consolidated Balance Sheets at fair value. We value our derivative and hedging instruments using quoted market prices and other significant unobservable inputs. We recognize changes in fair value and settlements of derivative instruments in Net (loss) gain on forward and derivative contracts - nonaffiliates and Net gain (loss) on forward and derivative contracts - affiliates in the Consolidated Statements of Operations as they occur. Unrealized gains on forward and derivative contracts are reported as part of cash flows from operations in the Consolidated Statements of Cash Flows. Foreign Currency – We are exposed to foreign currency risk due to fluctuations in the value of the U.S. dollar as compared to the Euro and the Icelandic krona ("ISK"), and the Chinese renminbi. Grundartangi, Vlissingen and Jamalco use the U.S. dollar as their functional currency, as contracts for sales of aluminum and alumina and purchases of alumina and power are denominated in U.S. dollars. Transactions denominated in currencies other than the functional currency are recorded based on exchange rates at the time such transactions arise and any transaction gains and losses are reflected in Other expense - net in the Consolidated Statements of Operations. Financial Instruments — Receivables, certain life insurance policies, payables, borrowings under revolving credit facilities and debt related to industrial revenue bonds ("IRBs") are carried at amounts that approximate fair value. Earnings per share — Basic earnings (loss) per share ("EPS") amounts are calculated by dividing Net income (loss) allocated to common stockholders by the weighted average number of common shares outstanding using the two-class method. Diluted EPS is calculated by dividing Net income (loss) allocated to common stockholders by the weighted average number of common and dilutive common equivalent shares outstanding during the period. Dilutive common equivalent shares are calculated using the more dilutive of either the if-converted or two-class methods. Our Series A Convertible Preferred Stock is a non-cumulative perpetual participating convertible preferred stock with no set dividend preferences. In periods where we report net losses, we do not allocate these losses to the Convertible Preferred Stock for the computation of basic or diluted EPS. Asset Retirement Obligations — We are subject to environmental regulations which create certain legal obligations related to the normal operations of our bauxite mine and alumina refinery and our domestic primary aluminum smelter operations. Our asset retirement obligations ("AROs") consist primarily of costs associated with mine reclamation obligations, closure of bauxite residue areas, landfill closure, and the disposal of spent potliner used in the reduction cells of our domestic smelters. AROs are recorded on a discounted basis at the time the obligation is incurred (when the potliner is put in service or upon disturbance of lands to be mined) and accreted over time for the change in the present value of the liability. We capitalize the asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful lives. Certain conditional asset retirement obligations ("CAROs") related to the remediation of our primary aluminum facilities for hazardous material, such as landfill materials and asbestos, have not been recorded because they have an indeterminate settlement date. CAROs are a legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within our control. Concentrations of Credit Risk — Financial instruments, which potentially expose us to concentrations of credit risk, consist principally of trade receivables. Our limited customer base increases our concentrations of credit risk with respect to trade receivables. We routinely assess the financial strength of our customers and collectability of our trade receivables and recognize an allowance based on our estimate of lifetime expected credit losses in accordance with the current expected credit loss model. Share-Based Compensation — We measure the cost of employee services received in exchange for an award of equity instruments based on the fair value of the award on the grant date. We recognize the cost over the period during which an employee is required to provide service in exchange for the award. We issue shares to satisfy the requirements of our share-based compensation plans. At this time, we do not plan to issue treasury shares to support our share-based compensation plans, but we may in the future. We award performance units to certain officers and employees. The performance units may be settled in cash or common stock at the discretion of the Board. We have not issued any stock options since 2009. Reclassification — Certain amounts in the prior period financial statements have been reclassified to conform to the presentation of the current period financial statements. These immaterial reclassifications had no effect on the previously reported net income or net cash flows. Restatement of Financial Statements Subsequent to the issuance of our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, the Company identified an error in its historical financial statements related to its accounting for the consolidation of its Jamalco joint venture whereby the Company previously used the proportionate method of consolidation for certain of Jamalco's net assets versus the full consolidation method. The Company determined that corrections to the financial statements for the impacts of this change were required for all impacted prior periods presented in this Form 10-K. Therefore, the Company has reflected these corrections in the consolidated financial statements for the periods presented in this Form 10-K and the consolidated financial statements previously included in each of the Company's Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2025, June 30, 2025 and September 30, 2025. Additionally, current and prior period amounts in the applicable notes to the consolidated financial statements have been corrected. See Note 22. Restatement of Previously Issued Financial Statements and Note 23. Quarterly Financial Information (Unaudited and Restated). Recent accounting pronouncements In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, that requires presentation of specific categories of reconciling items, as well as reconciling items that meet a quantitative threshold, in the reconciliation between the income tax provision and the income tax provision using statutory tax rates. The standard also requires disclosure of income taxes paid disaggregated by jurisdiction with separate disclosure of income taxes paid to individual jurisdictions that meet a quantitative threshold. The amendments in this accounting standard are effective for fiscal years beginning after December 15, 2024. The Company adopted this guidance for the 2025 annual reporting period on a prospective basis, resulting in additional disclosures within Note 16. Income Taxes. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40m as amended by ASU 2025-01): Disaggregation of Income Statement Expenses, that requires disclosure of the amounts of purchases of inventory, employee compensation, depreciation, and intangible asset amortization included in each relevant expense line item on the income statement. The standard also requires a qualitative description of other amounts included in each relevant expense line item on the income statement that are not separately disclosed. In addition, entities are required to disclose the nature and amount of selling expenses. The new standard is effective for fiscal years beginning after December 15, 2026, and interim periods beginning after December 15, 2027. Early adoption is permitted. We do not expect any impact to the consolidated financial statements, but the standard will require certain additional disclosures in the notes to the consolidated financial statements and the Company plans to adopt this guidance for the annual period ending December 31, 2027. In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities, which adds guidance on the recognition, measurement and presentation of government grants. The new standard is effective for fiscal years beginning after December 15, 2028. Early adoption is permitted. The Company has previously analogized to IAS 20, Accounting for Government Grants and Disclosure of Government Assistance, to account for refundable tax credits as an income grant. The Company's policy on income grants under IAS 20 aligns with the updated guidance, and the Company does not expect a material effect on its consolidated financial statements upon adoption.
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Acquisition of Jamalco |
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Dec. 31, 2025 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Acquisition of Jamalco | 2. Acquisition of Jamalco On May 2, 2023, our wholly-owned subsidiary, Century Aluminum Jamaica Holdings, Inc., completed the acquisition of all the outstanding share capital of General Alumina Holdings Limited, the holder of a 55% interest in Jamalco JV ("Jamalco"), an unincorporated joint venture engaged in bauxite mining and alumina production in Jamaica. The remaining 45% interest in Jamalco is owned by Clarendon Alumina Production Limited ("CAP"), which in turn is owned by the Government of Jamaica. The purchase price for the acquisition was $1.00. The acquisition resulted in a bargain purchase gain in part due to the seller experiencing financial distress following curtailment of Jamalco's operations in the second half of 2021 due to a facility fire, with operations restarting in the second half of 2022. The acquisition was accounted for as a business combination under the acquisition method of accounting in accordance with ASC 805 - Business Combinations, resulting in the Company recognizing the assets and liabilities at fair value with the excess over fair value of consideration transferred to the seller presented as a bargain purchase gain of $245.9 million recognized within the Consolidated Statements of Operations for the year ended December 31, 2024. During the first quarter of 2024, the Company finalized the Jamalco purchase price allocation and recognized measurement period adjustments, which primarily resulted from third-party valuation adjustments to risk premiums, reducing the value of property, plant and equipment by $29.0 million. This reduction in value of property plant and equipment resulted in a corresponding reduction to the bargain purchase gain of $29.0 million decreasing the value of the previously deferred bargain purchase gain of $273.4 million as of December 31, 2023. The Company finalized its purchase accounting as of March 31, 2024. The following table summarizes the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition:
For the twelve months ended December 31, 2023, Jamalco contributed $150.3 million to our total revenues and a loss of $45.4 million to our total earnings. In connection with the acquisition, the Company incurred approximately $1.4 million of transaction costs for the twelve months ended December 31, 2023, which are included in Selling, general and administrative expenses on the Consolidated Statements of Operations. The following unaudited pro forma financial information reflects the results of operations of the Company for the twelve months ended December 31, 2023 and 2022, respectively, as if the acquisition of Jamalco had been completed on January 1, 2022. This unaudited pro forma financial information has been prepared for informational purposes and is not necessarily indicative of the actual consolidated results of operations had the acquisition been completed on January 1, 2022, nor is the information indicative of future results of operations of the combined companies.
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Curtailment of Operations - Hawesville |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Restructuring and Related Activities [Abstract] | |
| Curtailment of Operations - Hawesville | 3. Curtailment of Operations - Hawesville In August 2022, we fully curtailed production at the Hawesville facility. For the year ended December 31, 2024, we incurred curtailment charges of $6.8 million. These charges were partially offset by income related to scrap and materials sales of $0.5 million. Comparatively, for the year ended December 31, 2023, we incurred curtailment charges of $16.6 million, including $9.0 million related to demand capacity charges for power. These charges were partially offset by income related to scrap and material sales of $1.7 million. For the year ended December 31, 2025, we incurred no additional curtailment charges or income. On February 2, 2026, we completed the sale of Hawesville. See Note 24. Subsequent Events for additional information on sales to the sale.
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Related Party Transactions |
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Related Party Transactions [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Related Party Transactions | 4. Related Party Transactions The significant related party transactions occurring during the years ended December 31, 2025, 2024 and 2023 are described below. All of our related party transactions are subject to the Company's Related Party Transaction Policy and are required to be made on an arm's length basis and on terms that are fair and reasonable to the Company and substantially the same as would apply if the other party was not a related party. We believe all of our transactions with related parties are at prices that approximate market. Glencore ownership As of December 31, 2025, Glencore plc and its affiliates (together "Glencore") beneficially owned 36.4% of Century’s outstanding common stock. In November 2025, Glencore sold 9,000,000 shares of Century's common stock. Due to the sale and in accordance with automatic conversion features of the Series A Convertible Preferred Stock, the remaining Series A Convertible Preferred Stock held by Glencore was converted into common stock. Century and Glencore enter into various transactions from time to time such as the purchase and sale of primary aluminum, purchase and sale of alumina and other raw materials, tolling agreements as well as forward financial contracts and borrowing and other debt transactions. Sales to Glencore For the years ended December 31, 2025, 2024 and 2023 we derived approximately 54.0%, 59.1% and 73.8% of our consolidated sales from Glencore, respectively. Glencore purchases aluminum produced at our U.S. smelters at prices based on the LME plus the Midwest regional delivery premium plus any additional market-based product premiums. Glencore purchases aluminum produced at our Grundartangi, Iceland smelter at prices based on the LME plus the European Duty Paid premium plus any additional market-based product premiums. We have entered into agreements with Glencore pursuant to which we sell certain amounts of alumina at market-based prices. For the years ended December 31, 2025, 2024 and 2023 we recorded $206.6 million, $191.3 million, and $191.7 million of revenue related to alumina sales to Glencore, respectively. Purchases from Glencore We purchase a portion of our alumina and certain other raw material requirements from Glencore. Alumina purchases from Glencore during 2025 were priced based on published alumina and aluminum indices as well as fixed prices. Financial contracts with Glencore From time to time, we enter into certain financial contracts with Glencore. See Note 20. Derivatives regarding these forward financial sales contracts. Summary A summary of the aforementioned significant related party sales and purchases for the years ended December 31, 2025, 2024 and 2023 is as follows:
(1)Includes settlements of financial contract positions. Vlissingen Credit Facility On December 9, 2022, Vlissingen entered into a Facility Agreement with Glencore International AG which was amended and extended on October 1, 2024 (as amended, the "Vlissingen Credit Facility"). The availability period for borrowings under the Vlissingen Credit Facility was extended by two years and now ends on December 2, 2026. Pursuant to the terms of the Vlissingen Credit Facility, Vlissingen may borrow from time to time up to $90 million in one or more loans at either (i) a fixed interest rate equal to 8.75% per annum (the "Fixed rate"), or (ii) a variable interest rate equal to the 1-month SOFR rate plus 3.687 percentage points, subject to an absolute maximum level of 9.00% and an absolute minimum level of 7.00% (the "Variable Rate"). The Fixed Rate is only applicable to borrowings made on or before December 1, 2024, after which the Variable Rate shall apply to all borrowings under the Vlissingen Credit Facility. See Note 8. Debt for additional information. Borrowings under the Facility Agreement are expected to be used for general corporate and working capital purposes of Century and its subsidiaries. Carbon Credit Repurchase Agreement In September 2023, our wholly owned subsidiary Nordural Grundartangi ehf ("Grundartangi"), entered into a structured repurchase arrangement with Glencore and sold 390,000 European Union Allowances ("Carbon Credits") at a price of €82.18 per Carbon Credit, for an aggregate amount of €32.1 million (the "Original Carbon Credit Agreement"). Pursuant to the terms of the Original Carbon Credit Agreement, Grundartangi would repurchase the same number of Carbon Credits at a price of €83.72 per Carbon Credit, for an aggregate amount of €32.7 million. The Original Carbon Credit Agreement was amended in December 2023, March 2024, August 2024 and December 2024, in each case to extend the repurchase window and increase the repurchase price (collectively, the "Amended Carbon Credit Agreement"). The Amended Carbon Credit Agreement (i) settled 19,300 Carbon Credits, (ii) extended the repurchase window from December 2024 to August 2025 for the remaining 370,700 Carbon Credits and (iii) revised the repurchase price to €69.16 per Carbon Credit, for an aggregate amount of €25.6 million. In August 2025, all 370,700 Carbon Credits subject to the Amended Carbon Credit Agreement were settled in full. On December 2023, Grundartangi also entered into a second structured repurchase agreement with Glencore pursuant to which it sold 40,000 Carbon Credits at a price of €69.30 per Carbon Credit and agreed to repurchase the same number of Carbon Credits at a price of €70.71 per Carbon Credit for an aggregate amount of €2.8 million (the "Second Carbon Credit Agreement"). In March 2024 and August 2024, the Second Carbon Credit Agreement was amended to (i) increase the number of Carbon Credits subject to the Second Carbon Agreement by 19,300 credits, (ii) extend the repurchase window from March 2024 to August 2024 with respect to all 59,300 Carbon Credits and (iii) revise the purchase price to €186.74 per Carbon Credit, for an aggregate amount of €11.1 million. In August 2024, all 59,300 Carbon Credits subject to the Second Carbon Credit Agreement were settled in full. Due to the repurchase element of these transactions, the Company retained substantially all of the remaining benefits of the assets and has accounted for the transaction as a financing arrangement in accordance with Revenue from Contracts with Customers Topic of the FASB ASC 606.
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| Revenue from Contract with Customer [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Revenue | 5. Revenue We enter into contracts to sell mainly primary aluminum to our customers. Revenue is recognized when our performance obligations with our customers are satisfied. Our obligations under the contracts are satisfied when we transfer control of our primary aluminum or alumina to our customers which is generally upon shipment or delivery to customer directed locations. The amount of consideration we receive, thus the revenue we recognize, is a function of volume delivered, market price of primary aluminum, which is based on the LME, plus regional premiums and any value-added product premiums or alumina which is based on the alumina pricing index, plus Atlantic differential. The payment terms and conditions in our contracts vary and are not significant to our revenue. We complete an appropriate credit evaluation for each customer at contract inception. Customer payments are due in arrears and are recognized as Accounts receivable - net and due from affiliates in our Consolidated Balance Sheets. In connection with our sales agreements with certain customers, including Glencore, we invoice the customer prior to physical shipment of goods for a majority of production generated from each of our U.S. domestic smelters. For those sales, revenue is recognized only when the customer has specifically requested such treatment and has made a commitment to purchase the product. The goods must be complete, ready for shipment and separated from other inventory with control over the goods passing to the customer. We must retain no further performance obligations. Contract liabilities are recorded when cash payments are received or due in advance of performance. As of December 31, 2025, and 2024, amounts recorded in Due to affiliates were $31.2 million and $41.2 million, respectively. We disaggregate our revenue by geographical region as follows:
The table below shows the amount of net sales to external customers for each of the Company's product categories which accounted for 10% or more of consolidated net sales in either period for the years ended December 31, 2025, 2024 and 2023.
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Leases |
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| Leases [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Leases | 6. Leases We are a lessee in various agreements for the lease of office space, land, automobiles, and mobile equipment. All of our leases are considered operating leases. The weighted average remaining lease term for our operating leases was 9.2 years as of December 31, 2025 and 10.1 years as of December 31, 2024. Certain lease payment amounts are variable in nature and change periodically based on the local market consumer price index. The weighted average discount rate for our operating leases was 7.4% as of December 31, 2025 and 7.5% as of December 31, 2024. Our ROUA and lease liability balances for the years ended December 31, 2025 and December 31, 2024 were as follows:
(1)ROUA was recorded as part of Other Assets within non-current assets at December 31, 2025 and 2024. (2)Lease liability - current was recorded as part of Accrued and other current liabilities within current liabilities at December 31, 2025 and 2024. (3)Lease liability - non-current was recorded as part of Other liabilities within non-current liabilities at December 31, 2025 and 2024. The undiscounted maturities of our operating lease liability balances as of December 31, 2025 are as follows:
During 2025 and 2024, we entered into new lease obligations, which resulted in $3.7 million and $2.0 million of additional right of use assets, respectively. Total operating expense includes the following:
(1)Total lease expense is included in Cost of goods sold and Selling, general, and administrative expenses on the Consolidated Statements of Operations. We had cash outflows of $5.3 million, $5.0 million and $4.6 million for amounts included in the lease liability balance at the beginning of the year related to our operating leases for the years ended December 31, 2025, 2024 and 2023, respectively.
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Fair Value Measurements |
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| Fair Value Disclosures [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value Measurements | 7. Fair Value Measurements We measure certain of our assets and liabilities at fair value. Fair value represents the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In general, reporting entities should apply valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are developed using market data and reflect assumptions that market participants would use when pricing the asset or liability. Unobservable inputs are developed using the best information available about the assumptions and estimates that market participants would use when pricing the asset or liability. The fair value hierarchy provides transparency regarding the inputs we use to measure fair value. We categorize each fair value measurement in its entirety into the following three levels, based on the lowest level input that is significant to the entire measurement: •Level 1 Inputs – quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date. •Level 2 Inputs – inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. •Level 3 Inputs – unobservable inputs for the asset or liability.
(1)Trust assets are currently invested in money market funds. These trust assets are held to fund the non-qualified supplemental executive pension benefit obligations for certain of our officers. The following section describes the valuation techniques and inputs used for fair value measurements categorized within Level 2 of the fair value hierarchy:
When valuing Level 3 assets and liabilities, we use certain significant unobservable inputs. Management incorporates various inputs and assumptions including forward commodity prices, commodity price volatility and macroeconomic conditions, including interest rates and discount rates. Our estimates of significant unobservable inputs are ultimately based on our estimates of risks that market participants would consider when valuing our assets and liabilities. As of the years ending December 31, 2025, and December 31, 2024, there were no Level 3 assets and liabilities.
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| Debt | 8. Debt
(1)The IRBs are classified as current liabilities because they are remarketed weekly and could be required to be repaid upon demand if there is a failed remarketing. The interest rate at December 31, 2025 was 3.45%. (2)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.25%. (3)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.23%. (4)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.56% 6.875% Senior Secured Notes due 2032 General. On July 22, 2025, we issued $400.0 million in aggregate principal amount of 6.875% senior secured notes due 2032 (the "Notes"). We received proceeds of $393.7 million, after payment of certain financing fees and related expenses. Interest Rate. The 2032 Notes bear interest semi-annually in arrears on February 1 and August 1 of each year, beginning on February 1, 2026, at a rate of 6.875% per annum in cash. Maturity. The 2032 Notes mature on August 1, 2032. Seniority. The 2032 Notes are senior secured obligations of Century, ranking equally in right of payment with all existing and future senior indebtedness of Century, but effectively senior to unsecured debt to the extent of the value of collateral. Guaranty. Our obligations under the 2032 Notes are guaranteed by all of our existing and future domestic restricted subsidiaries (the “Guarantor Subsidiaries”), except for foreign owned holding companies, any domestic restricted subsidiary that owns no assets other than equity interests or other investments in foreign subsidiaries and certain immaterial subsidiaries, which guaranty shall in each case be a senior secured obligation of such Guarantor Subsidiaries, ranking equally in right of payment with all existing and future senior indebtedness of such Guarantor Subsidiaries but effectively senior to unsecured debt to the extent of the value of collateral. Collateral. Our obligations under the 2032 Notes and the Guarantor Subsidiaries' obligations under the guarantees are secured by a pledge of and lien on (subject to certain exceptions): (i) all of our and the Guarantor Subsidiaries' property, plant and equipment (other than certain excluded property); (ii) all equity interests in subsidiaries directly owned by Century or any Guarantor Subsidiaries; and (iii) proceeds of the foregoing. Under certain circumstances, the indenture and the security documents governing the 2032 Notes will permit us and the Guarantors to incur additional debt that also may be secured by liens on the collateral that are equal to or have priority over the liens securing the 2032 Notes. The collateral agent for the 2032 Notes will agree with the collateral agent for the other debt holders and us under such circumstances to enter into an intercreditor agreement that will cause the liens securing the 2032 Notes to be contractually subordinated to the liens securing such additional debt. Redemption Rights. Prior to August 1, 2028, we may redeem the 2032 Notes, in whole or in part, at a redemption price equal to 100.00% of the principal amount plus a make-whole premium and accrued and unpaid interest, and if redeemed during the twelve-month period beginning on August 1 of the years indicated below, at the following redemption prices plus accrued and unpaid interest:
Upon a change of control (as defined in the indenture governing the 2032 Notes), we will be required to make an offer to purchase the 2032 Notes at a purchase price equal to 101% of the outstanding principal amount of the 2032 Notes on the date of the purchase, plus accrued and unpaid interest to, but not including, the date of purchase. Covenants. The indenture governing the 2032 Notes contains customary covenants which may limit our ability, and the ability of certain of our subsidiaries, to: (i) incur additional debt; (ii) incur additional liens; (iii) pay dividends or make distributions in respect of capital stock; (iv) purchase or redeem capital stock; (v) make investments or certain other restricted payments; (vi) sell assets; (vii) issue or sell stock of certain subsidiaries; (viii) enter into transactions with shareholders or affiliates; and (ix) effect a consolidation or merger. Fair Value. As of December 31, 2025, the total estimated fair value of the 2032 Notes was $412.5 million. Although we use quoted market prices for identical debt instruments, the markets on which they trade are not considered to be active and are therefore considered Level 2 fair value measurements. 7.5% Senior Secured Notes due 2028 On July 22, 2025, we determined that all conditions precedent to the redemption (the “Redemption”) of our 2028 Notes pursuant to its Conditional Notice of Full Redemption issued on July 21, 2025 had been satisfied. Accordingly, the 2028 Notes were redeemed on August 5, 2025, at an aggregate redemption price of $261.1 million, consisting of 101.875% of the principal due and payable on the 2028 Notes plus accrued and unpaid interest to but excluding the August 5, 2025, redemption date. In connection with the Redemption, effective July 22, 2025, the Company satisfied and discharged all its obligations under and in accordance with the terms of the indenture governing the 2028 Notes. Based on the characteristics of the 2028 Notes and the 2032 Notes that were issued, the redemption of the 2028 Notes were accounted for as an extinguishment. Accordingly, we have recorded a $6.2 million loss on early extinguishment of debt, consisting of early redemption premiums of $4.7 million and a write-off of deferred financing costs associated with the 2028 Notes of $1.5 million. 2.75% Convertible Notes due 2028 General. On April 9, 2021, we completed a private offering of $86.3 million aggregate principal amount of convertible senior notes due 2028 (the "Convertible Notes"). The Convertible Notes were issued at a price of 100% of their aggregate principal amount. We received proceeds of $83.7 million, after payment of certain financing fees and related expenses. The initial conversion rate for the Convertible Notes is 53.3547 shares of the Company's common stock per $1,000 principal amount of Convertible Notes, which is equivalent to an initial conversion price of approximately $18.74 per share of the Company's common stock. The conversion rate and conversion price are subject to customary adjustments under certain circumstances in accordance with the terms of the indenture. Interest Rate. The Convertible Notes will bear interest semi-annually in arrears on May 1 and November 1 of each year, beginning on November 1, 2021, at a rate of 2.75% per annum in cash. Maturity. The Convertible Notes will mature on May 1, 2028, unless earlier converted, repurchased, or redeemed. Seniority. The Convertible Notes are the Company’s senior unsecured obligations and rank senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Convertible Notes; equal in right of payment to any of the Company’s unsecured indebtedness that is not so subordinated; effectively junior in right of payment to any of the Company’s senior secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries. Redemption rights. On or after May 6, 2025, we may redeem for cash all or part of the Convertible Notes at our option if the last reported sale price of our common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading-day period (including the last trading day of such period) ending on and including the trading day immediately preceding the date on which we provide notice of redemption, at a redemption price equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus accrued and unpaid interest. Upon conversion, we may satisfy our conversion obligation by paying or delivering, as applicable, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, based on the applicable conversion rate. In addition, if certain corporate events that constitute a make-whole fundamental change (as defined in the indenture) occur, then the conversion rate will, in certain circumstances, be increased for a specified period of time. Additionally, in the event of a corporate event constituting a fundamental change (as defined in the indenture), holders of the Convertible Notes may require us to repurchase all or a portion of their Convertible Notes at a repurchase price equal to 100% of the principal amount of the Convertible Notes being repurchased, plus accrued and unpaid interest to, but excluding, the date of the fundamental change repurchase. As of December 31, 2025, the if-converted value of the Convertible Notes exceeded the outstanding principal amount. Fair Value. As of December 31, 2025, the total estimated fair value of the Convertible Notes was $181.9 million. Although we use quoted market prices for identical debt instruments, the markets on which they trade are not considered to be active and are therefore considered Level 2 fair value measurements. U.S. Revolving Credit Facility General. We and certain of our direct and indirect domestic subsidiaries (the "Borrowers") have a senior secured revolving credit facility with a syndicate of lenders (the "U.S. revolving credit facility"). On June 14, 2022 we amended our U.S. revolving credit facility, increasing our borrowing capacity to $250.0 million, including up to $150.0 million under a letter of credit sub-facility. On July 22, 2025, we further amended the U.S. revolving credit facility to, among other items, extend the maturity date of the facility to July 22, 2030 and revise the calculation of Term SOFR Adjustment to 0.10% per annum for all interest periods. Any letters of credit issued and outstanding under the U.S. revolving credit facility reduce our borrowing availability on a dollar-for-dollar basis. At December 31, 2025, there were no outstanding borrowings and $50.5 million of outstanding letters of credit issued under our U.S. revolving credit facility. Principal payments, if any, are due upon maturity of the U.S. revolving credit facility and may be prepaid without penalty.
Borrowing Base. The availability of funds under the U.S. revolving credit facility is limited by a specified borrowing base consisting of the Borrower's accounts receivable and inventory which meet the eligibility criteria. Guaranty. The Borrowers' obligations under the U.S. revolving credit facility are guaranteed by certain of our domestic subsidiaries and secured by a continuing lien upon and a security interest in all of the Borrowers' accounts receivable, inventory and certain bank accounts. Each Borrower is liable for any and all obligations under the U.S. revolving credit facility on a joint and several basis. Interest Rates and Fees. Any amounts outstanding under the U.S. revolving credit facility will bear interest at our option of either the secured overnight financing rate ("SOFR") or a base rate, plus, in each case, an applicable interest margin. The applicable interest margin is determined based on the average daily availability for the immediately preceding quarter. In addition, we pay an unused line fee on undrawn amounts, less the amount of our letters of credit exposure. For standby letters of credit, we are required to pay a fee on the face amount of such letters of credit that varies depending on whether the letter of credit exposure is cash collateralized. Prepayments. We can make prepayments of amounts outstanding under the U.S. revolving credit facility, in whole or in part, without premium or penalty, subject to standard breakage costs, if applicable. We may be required to apply the proceeds from sales of collateral accounts, other than sales of inventory in the ordinary course of business, to repay amounts outstanding under the revolving credit facility and correspondingly reduce the commitments there under. Covenants. The U.S. revolving credit facility contains customary covenants, including restrictions on mergers and acquisitions, indebtedness, affiliate transactions, liens, dividends and distributions, dispositions of collateral, investments, and prepayments of indebtedness, as well as a covenant that requires the Borrowers to maintain certain minimum liquidity or availability requirements. Events of Default. The U.S. revolving credit facility also includes customary events of default, including nonpayment, misrepresentation, breach of covenant, bankruptcy, change of ownership, certain judgments and certain cross defaults. Upon the occurrence of an event of default, commitments under the U.S. revolving credit facility may be terminated and amounts outstanding may be accelerated and declared immediately due and payable. Iceland Revolving Credit Facility General. Our wholly-owned subsidiary, Nordural Grundartangi ehf ("Grundartangi"), entered into a revolving credit facility agreement with Landsbankinn hf., as amended (the "Iceland revolving credit facility") which provides for borrowings of up to $100.0 million in the aggregate. Under the terms of the Iceland revolving credit facility, when Grundartangi borrows funds it will designate a repayment date, which may be any date prior to the maturity of the Iceland revolving credit facility. At December 31, 2025, there was $61.0 million in outstanding borrowings under our Iceland revolving credit facility. The Iceland revolving credit facility has a term through December 2026.
Borrowing Base. The availability of funds under the Iceland revolving credit facility is limited by a specified borrowing base consisting of inventory and accounts receivable of Grundartangi. Security. Grundartangi's obligations under the Iceland revolving credit facility are secured by a general bond under which Grundartangi's inventory and accounts receivable are pledged to secure full payment of the loan. Interest Rates and Fees. Any amounts outstanding under the Iceland revolving credit facility will bear interest at SOFR plus a margin per annum. Prepayments. Any outstanding borrowings may be prepaid without penalty or premium in whole or in part. Covenants. The Iceland revolving credit facility contains customary covenants, including restrictions on mergers and acquisitions, dispositions of assets, compliance with permits, laws and payment of taxes, as well as a covenant that requires Grundartangi to maintain a certain minimum equity ratio. Events of Default. The Iceland revolving credit facility also includes customary events of default, including nonpayment, loss of license, cessation of operations, unlawfulness, breach of covenant, bankruptcy, change of ownership, certain judgments and certain cross defaults. Upon the occurrence of an event of default, commitments under the Iceland revolving credit facility may be terminated and amounts outstanding may be accelerated and declared immediately due and payable. Grundartangi Casthouse Facility In October 2025, we fully repaid all outstanding borrowings under the Casthouse Facility, which totaled $116.4 million in outstanding borrowings and $1.9 million in interest. As a result, the Casthouse Facility has been extinguished, and we recorded a $1.5 million loss on early extinguishment of debt, consisting of a write-off of deferred financing costs. Vlissingen Credit Facility On December 9, 2022, Vlissingen entered into a Facility Agreement with Glencore International AG, which was amended and extended on October 1, 2024 (as amended, the "Vlissingen Credit Facility"). The availability period for borrowings under the Vlissingen Credit Facility was extended by two years and now ends on December 2, 2026. Pursuant to the terms of the Vlissingen Credit Facility, Vlissingen may borrow from time to time up to $90 million in one or more loans. As of December 31, 2025, there was no outstanding borrowings under the Vlissingen Facility Agreement. Security. Vlissingen’s obligations under the Vlissingen Credit Facility are secured by liens on the ground lease on which Vlissingen’s facilities are located, Vlissingen’s moveable assets, financial assets, receivables and other assets, and Vlissingen’s shares. Interest Rates and Fees. Amounts outstanding under the Vlissingen Credit Facility will bear interest at either (i) a fixed interest rate equal to 8.75% per annum (the "Fixed Rate"), or (ii) a variable interest rate equal to the 1-month SOFR rate plus 3.687 percentage points, subject to an absolute maximum level of 9.00% and an absolute minimum level of 7.00% (the "Variable Rate"). The Fixed Rate is only applicable to borrowings made on or before December 1, 2024, after which the Variable Rate shall apply to all borrowings under the Vlissingen Credit Facility. Prepayments. Any outstanding borrowings may be prepaid without penalty or premium in whole or in part without any charge, fee premium or penalty. Covenants. The Vlissingen Credit Facility contains customary covenants including with respect to mergers, guarantees and preservation and dispositions of assets. Events of Default. The Vlissingen Credit Facility also includes customary events of default, including nonpayment, breach of any provision or representation under the agreement, and certain cross-default and insolvency events. Upon the occurrence of an event of default, commitments under the Vlissingen Credit Facility may be terminated and amounts outstanding may be accelerated and declared immediately due and payable. Covenant Compliance As of December 31, 2025, we and our subsidiaries were in compliance with all financial covenants or maintained availability above applicable covenant triggers. Hancock County Industrial Revenue Bonds As part of the purchase price for our acquisition of the Hawesville facility, we assumed IRBs which were issued in connection with the financing of certain solid waste disposal facilities constructed at the Hawesville facility. The IRBs bear interest at a variable rate not to exceed 12% per annum determined weekly based upon prevailing rates for similar bonds in the industrial revenue bond market and interest on the IRBs is paid quarterly. The IRBs are secured by a letter of credit issued under our U.S revolving credit facility and mature in April 2028. Surety Bond Facility As part of our normal business operations, we are required to provide surety bonds or issue letters of credit in certain states in which we do business as collateral for certain workers' compensation obligations. In June 2022, we entered into a surety bond facility with an insurance company to provide such bonds when applicable. As of December 31, 2025, we had issued surety bonds totaling $6.6 million. As we had previously guaranteed our workers' compensation obligations through issuance of letters of credit against our revolving credit facility, the surety bond issuance increases credit facility availability.
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Shareholders' Equity |
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| Stockholders' Equity Note [Abstract] | |
| Shareholders' Equity | 9. Shareholders' Equity Common Stock As of December 31, 2025 and 2024, we had 195,000,000 shares of common stock, $0.01 cent par value, authorized under our Restated Certificate of Incorporation, of which 106,155,528 shares were issued and 98,969,007 shares were outstanding at December 31, 2025; 100,475,086 shares were issued and 93,288,565 shares were outstanding at December 31, 2024. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of our preferred stock which are currently outstanding, including our Series A Convertible Preferred Stock, or which we may designate and issue in the future. Preferred Stock As of December 31, 2025 and 2024, we had 5,000,000 shares of preferred stock, $0.01 cent par value per share, authorized under our Restated Certificate of Incorporation. Our Board of Directors may issue preferred stock in one or more series and determine for each series the dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking fund terms and the number of shares constituting that series, as well as the designation thereof. Depending upon the terms of preferred stock established by our Board of Directors, any or all of the preferred stock could have preference over the common stock with respect to dividends and other distributions and upon the liquidation of Century. In addition, issuance of any shares of preferred stock with voting powers may dilute the voting power of the outstanding common stock. Series A Convertible Preferred Stock Shares Authorized and Outstanding. In 2008, we issued 160,000 shares of our Series A Convertible Preferred Stock. Glencore held all of the issued and outstanding Series A Convertible Preferred Stock. At December 31, 2024, 49,715 shares were outstanding. In November 2025, Glencore sold 9,000,000 shares of our common stock. Due to the sale, and in accordance with automatic conversion features of the Series A Convertible Preferred Stock, the remaining Series A Convertible Preferred Stock held by Glencore were converted into common stock. As of December 31, 2025, there were no shares outstanding. The conversion of preferred to common shares was 100 shares of common for each share of preferred stock. Our Series A Convertible Preferred Stock had a par value of $0.01 per share. Stock Repurchase Program In 2011, our Board of Directors authorized a $60.0 million stock repurchase program and during the first quarter of 2015, our Board of Directors increased the size of the program by $70.0 million. Under the program, Century is authorized to repurchase up to $130.0 million of our outstanding shares of common stock, from time to time, on the open market at prevailing market prices, in block trades or otherwise. The timing and amount of any shares repurchased will be determined by our management based on its evaluation of market conditions, the trading price of our common stock and other factors. The stock repurchase program may be suspended or discontinued at any time. Shares of common stock repurchased are recorded at cost as treasury stock and result in a reduction of shareholders’ equity in the Consolidated Balance Sheets. From time to time, treasury shares may be reissued as contributions to our employee benefit plans and for the conversion of preferred stock. When shares are reissued, we use an average cost method for determining cost. The difference between the cost of the shares and the reissuance price is added to or deducted from additional paid-in capital. Through December 31, 2025, we repurchased 7,186,521 shares of common stock for an aggregate purchase price of $86.3 million. We have made no repurchases since April 2015 and have approximately $43.7 million remaining under the repurchase program authorization as of December 31, 2025.
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| Inventories | 10. Inventories Inventories, at December 31, consist of the following:
For the year ended December 31, 2025, we recorded an inventory markdown of $8.4 million within Other operating expenses - net related to inventory at Hawesville that was sold during the first quarter of 2026 at a price below its carrying value.
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| Property, Plant and Equipment | 11. Property, Plant and Equipment Property, plant and equipment, at December 31, consist of the following:
For the years ended December 31, 2025, 2024 and 2023, we recorded depreciation, amortization and depletion expense of $91.8 million, $86.7 million, and $79.0 million, respectively.
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| Accumulated Other Comprehensive Loss ("AOCL") | 12. Accumulated Other Comprehensive Loss ("AOCL")
(1)The allocation of the income tax effect to the components of other comprehensive loss is as follows:
The following table summarizes the changes in the accumulated balances for each component of AOCL:
Reclassifications out of AOCL were included in the Consolidated Statements of Operations as follows:
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Pension and Other Postretirement Benefits |
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| Retirement Benefits [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Pension and Other Postretirement Benefits | 13. Pension and Other Postretirement Benefits Pension Benefits We maintain noncontributory defined benefit pension plans for certain foreign and domestic hourly and salaried employees. For the eligible domestic salaried employees, plan benefits are based primarily on years of service and average compensation during the later years of employment. For hourly employees, plan benefits are based primarily on a formula that provides a specific benefit for each year of service. Plan benefits are available to all permanent foreign employees. Our funding policy is to contribute amounts based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements of the Employee Retirement Income Security Act of 1974 ("ERISA"). In addition, we maintain the supplemental executive retirement benefit ("SERB") plan for certain current and former executive officers, which is frozen to future accruals. Other Postretirement Benefits ("OPEB") In addition to providing pension benefits, we provide certain healthcare and life insurance benefits for certain foreign and domestic retired employees. We accrue the estimated cost of providing postretirement benefits during the working careers of those employees who could become eligible for such benefits when they retire. We fund these benefits as the retirees submit claims. Retiree medical welfare changes Under the current Hawesville labor agreement, employees who retire during the term of the labor agreement have been divided into sub-groups based on attributes such as Medicare eligibility, hire date, age and years of service. Levels of benefits are defined for the sub-groups and range from no substantive change from the benefits provided under the previous labor agreement to replacement of the defined retiree medical benefit program with individual health reimbursement accounts for each eligible participant. The health reimbursement accounts are funded based on established rates per hour worked by each eligible participant. Eligible participants will be able to withdraw from their health reimbursement accounts to fund their own retiree medical coverage. On February 13, 2026, we terminated our labor agreement with United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USW") for former employees at our Hawesville facility. See "Participation in Multi-employer Pension Plans" below for additional information. During 2017, the Company amended its non-union retiree medical and life insurance benefits to align the Company’s benefits with the market and achieve a uniform retiree medical benefit design across the Company’s U.S. locations. Effective January 1, 2018, non-union retiree medical and life insurance benefits are restricted to current participants who meet the eligibility criteria as of January 1, 2018. Additionally, effective January 1, 2019, Century no longer administers non-union retiree medical, prescription drug, dental, or vision benefits and instead makes fixed health reimbursement account contributions. Obligation and Funded Status The change in benefit obligation and change in plan assets as of December 31 are as follows:
The increase in the defined benefit plans' benefit obligation was mainly driven by actuarial gains in 2025, which were primarily attributable to the changes in the discount rates from fiscal year 2024 to 2025. The decrease in OPEB plans' benefit obligation was mainly driven by a change in the post-65-years-of-age participant insurance coverage for post-65-years-of-age participants from fiscal year 2024 to 2025.
The change in actual return on plan assets in 2025 was primarily attributable to fluctuations in market prices during the year.
Pension Plans That Are Not Fully Funded At December 31, 2025, the projected benefit obligation, accumulated benefit obligation and fair value of plan assets for the pension plans with accumulated benefit obligations in excess of plan assets were $347.4 million, $318.0 million, and $288.7 million, respectively. At December 31, 2024, the projected benefit obligation, accumulated benefit obligation and fair value of plan assets for the pension plans with accumulated benefit obligations in excess of plan assets were $342.5 million, $303.4 million and $272.2 million, respectively. Components of net periodic benefit cost and other amounts recognized in other comprehensive income (loss): Net Periodic Benefit Cost:
Other changes in Plan Assets and Benefit Obligations Recognized in Accumulated Other Comprehensive Income (Loss) (pre-tax):
Weighted average assumptions used to determine benefit obligations at December 31:
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
(1)We use the Ryan Above Median Yield Curve to determine the discount rate. (2)For 2025, the rate of compensation increase is 3.2%. For 2024, the rate of compensation increase was 3.5%. For 2023, the rate of compensation increase was 4% per year for the first year and 3.5% per year thereafter. (3)The rate for each of our defined benefit plans was selected by taking into account our expected asset mix and is based on historical performance as well as expected future rates of return on plan assets. For measurement purposes, medical cost inflation for locations other than Jamaica is initially estimated to be 8.5% for both pre- and post-65-years-of-age participants, declining to 4.5% over ten years and continuing thereafter. For Jamaica, it is initially estimated to be 8.0% for both pre- and post-65-years-of-age participants and for the next two years. Benefit Plan Assets Pension Plan Investment Strategy and Policy The Pension Plans’ assets are invested in a prudent manner for the exclusive purpose of providing benefits to participants. Other objectives are to: •Provide a total return that, over the long term, provides sufficient assets to fund the pension plan liabilities subject to a level of risk, contributions and pension expense deemed appropriate by the company. •Minimize, where possible, pension expense volatility, and inclusion of liability driven investing as an investment strategy when appropriate. As the funding ratio improves, the objectives will evolve to minimize the funded status volatility. •Diversify investments within asset classes to reduce the impact of losses in single investments. The assets of the Pension Plans are invested in compliance with ERISA, as amended, and any subsequent applicable regulations and laws. Performance Our performance objective is to outperform the return of weighing passive investment alternatives by the policy target allocations after fees at a comparable level of risk. This investment objective is expected to be achieved over the long term and is measured over rolling multi-year periods. Peer-relative performance comparisons will also be considered especially when performance deviates meaningfully from market indexes. Investment objectives for each asset class are included below. Asset Allocation Policy Asset allocation policy is the principal method for achieving the Pension Plans' investment objectives stated above. The Pension Plans’ weighted average long-term strategic asset allocation policy targets are as follows:
Global equities are held for their long-term expected return premium over fixed income investments and inflation. Fixed income is held for diversification relative to equities, and as a hedging instrument to interest rate volatility for the pension obligation. Diversified Credit and Real Assets are held for diversification relative to equities and for income generation. The strategic role of global equities is to: •Provide higher expected returns of the major asset classes. •Maintain a diversified exposure within global stock markets through the use of multi-manager portfolio strategies. The strategic role of fixed income is to: •Diversify the Pension Plans’ equity exposure by investing in fixed income securities that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio. •Maintain a diversified exposure within the U.S. fixed income market through the use of portfolio strategies targeting treasury bond exposures. •Hedge the interest rate risk of the pension obligation by investing in securities that target a similar duration to the pension obligation cash flows. The strategic role of diversified credit is to: •Diversify the Pension Plans’ equity exposure by investing in alternative credit securities that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio. •Maintain a diversified exposure within the alternative credit markets through the use of multi-manager portfolio strategies targeting, but not limited to, securitized credit, high yield securities, and emerging market debt. •Achieve returns in excess of passive indexes through the use of active investment managers and strategies. The strategic role of real assets is to: •Diversify the Pension Plans’ equity exposure by investing in real assets that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio. •Maintain a diversified exposure within the real asset markets through the use of multi-manager portfolio strategies targeting listed and unlisted exposures. •Achieve returns in excess of passive indexes through the use of active investment managers and strategies. The long-term strategic asset allocation policy is reviewed regularly or whenever significant changes occur to Century’s or the Pension Plans' financial position and liabilities. Fair Value Measurements of Pension Plan assets The following table sets forth by level the fair value hierarchy our Pension Plans' assets. These assets are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and the placement within the fair value hierarchy levels. As more fully described within Note 7. Fair Value Measurements, the Company uses a three-level fair value hierarchy that prioritizes the inputs used to measure fair values. The fair value hierarchy provides transparency regarding the inputs we use to measure fair value. We categorize each fair value measurement in its entirety into the following three levels, based on the lowest level input that is significant to the entire measurement: •Level 1 Inputs – quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date. •Level 2 Inputs – inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. •Level 3 Inputs – unobservable inputs for the asset or liability. The following summarizes the Company’s Pension Plans' assets fair value by asset category:
Our domestic Pension Plans’ assets are held in certain commingled funds and group trusts which do not have publicly quoted prices. The fair value of the commingled funds and group trusts is based on NAV of the underlying investments. The fair value of the underlying investments held by the commingled funds, separate accounts and common collective trusts is generally based on quoted prices in active markets. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. Our foreign plan assets are held in bonds and equity securities which have publicly quoted prices. Our other postretirement benefit plans are unfunded. We fund these benefits as the retirees submit claims. Pension and OPEB Cash Flows During 2025 and 2024, we made contributions of approximately $9.2 million and $2.5 million, respectively, to the qualified defined benefit and SERB plans we sponsor and $5.0 million and $5.5 million, respectively, to the other postretirement benefit plans. We expect to make the following contributions for 2026:
Estimated Future Benefit Payments The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
Participation in Multi-employer Pension Plans The union-represented employees at Hawesville are part of a United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USW") sponsored multi-employer plan. Our contributions to the plan are determined at a fixed rate per hour worked. The risks of participating in a multi-employer plan are different from single employer plans in the following respects: •Assets contributed to the multiemployer plan by one employer may be used to provide benefits to employees of other participating employers. •If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers. •If a participating employer chooses to stop participating in a multi-employer plan, the employer may be required to pay the plan an amount based on the underfunded status of the plan, referred to as a withdrawal liability. Century’s participation in the plan for the year ended December 31, 2025, is outlined in the table below.
(1)The "EIN/Pension Plan Number" column provides the Employee Identification Number (EIN) and the three-digit plan number, if applicable. (2)The most recent Pension Protection Act zone status available in 2025 and 2024 is for the plan's year-end December 31, 2024 and December 31, 2023, respectively. The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the red zone are generally less than 65 percent funded, plans in the yellow zone are less than 80 percent funded, and plans in the green zone are at least 80 percent funded. (3)The “Subject to Financial Improvement / Rehabilitation Plan” column indicates plans for which a financial improvement plan (FIP) or a rehabilitation plan (RP) is either pending or has been implemented. The last column lists the expiration date(s) of the collective-bargaining agreement(s) to which the plans are subject. On February 13, 2026, we terminated our labor agreement with USW for former employees at our Hawesville facility. Century's contributions to the above plan is not 5% or more of the total contributions to the plan. Century 401(k) Plans We sponsor a tax-deferred savings plan under which eligible domestic employees may elect to contribute specified percentages of their compensation with Century. We match a portion of participants' contributions to the savings plan. Employee and matching contributions are considered fully vested immediately upon participation in the plan. Concurrent with the 2014 amendment to the Salaried Pension Plan that eliminated future accruals for participants who are under age 50 as of January 1, 2015 and closed the plan to new entrants, the Company increased the proportional match of contributions made to those affected by the amendment. The expense related to the plan was $6.7 million, $6.3 million, and $5.8 million for 2025, 2024, and 2023, respectively.
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Share-based Compensation |
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| Share-Based Payment Arrangement [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share-based Compensation | 14. Share-based Compensation Amended and Restated Stock Incentive Plan. Under our Amended and Restated Stock Incentive Plan (the "Stock Incentive Plan") we award service-based and performance-based share awards and nonqualified stock options to our salaried officers, non-employee directors, and other key employees. Our service-based and performance-based share awards typically vest over a period of three years from the date of grant, provided that the recipient is still our employee at the time of vesting. Our independent non-employee directors receive annual grants of service-based share awards that typically vest following 12 months of service. The Stock Incentive Plan has 12,900,000 shares authorized for issuance with approximately 1,899,785 shares remaining at December 31, 2025. Long-Term Incentive Plan. We also grant annual long-term incentive awards under our Amended and Restated Long-Term Incentive Plan (the "LTIP"). The LTIP is designed to provide senior-level employees the opportunity to earn long-term incentive awards through the achievement of performance goals and to align compensation with the interests of our stockholders. This is achieved by linking compensation to share price appreciation and total stockholder return over a multi-year period. Awards made under the LTIP are granted subject to the Stock Incentive Plan to the extent the award is deliverable in stock. We provide two types of LTIP awards: restricted stock units ("RSU") and performance stock units ("PSU"). RSUs are stock-settled awards which do not contain any performance-based vesting requirements. PSUs can be settled in cash or stock and vest based on the achievement of pre-determined performance metrics at the discretion of the Board. Our PSU liability, a component of both Accrued other current liabilities Other liabilities on the Consolidated Balance Sheets, was approximately $11.8 million and $7.1 million as of December 31, 2025 and 2024, respectively. Both the PSUs and RSUs vest, in their entirety, after three years.
Fair Value Measurement of Share-Based Compensation Awards. For our service-based awards, fair value is equal to the closing stock price on the date of grant. For our performance-based awards, fair value is equal to the closing stock price at each reporting period end. The following table summarizes the compensation cost recognized for the years ended December 31, 2025, 2024 and 2023 for all service-based and performance-based share awards. The compensation cost is included as part of Selling, general and administrative expenses and Cost of goods sold in our Consolidated Statements of Operations.
No share-based compensation cost was capitalized during these periods and there were no significant modifications of any share-based awards in 2025, 2024 and 2023. As of December 31, 2025, we had unrecognized compensation cost of $23.5 million before taxes. This cost will be recognized over a weighted average period of 1.2 years.
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| Earnings Per Share | 15. Earnings Per Share The following table shows the basic and diluted EPS for 2025, 2024, and 2023:
(1)In periods when we report a net loss, all share-based compensation awards, convertible preferred shares and convertible senior notes are excluded from the calculation of diluted weighted average shares outstanding because of their anti-dilutive effect on earnings (loss) per share.
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Income Taxes |
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| Income Tax Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income Taxes | 16. Income Taxes In 2025, the Company adopted ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, on a prospective basis. This guidance requires disaggregated information about the effective tax rate reconciliation, additional disaggregated data on income taxes paid by jurisdiction, and certain other amendments to improve the effectiveness of income tax disclosures. The adoption did not impact the Company’s consolidated financial position, results of operations, or cash flows but enhanced the income tax footnote disclosures for the year ended December 31, 2025. The components of pre-tax book income (loss) consist of the following:
Significant components of income tax expense consist of the following:
A reconciliation of the statutory U.S. Federal income tax rate to the effective income tax rate on income (loss) is as follows:
(1)State taxes in Tennessee and Kentucky comprise the majority (greater than 50 percent) of the tax effect in this category. The effective tax rate for the year ending December 31, 2025 was (482.7)% compared to the statutory US tax rate of 21%. This lower effective rate is primarily due to the non-taxable benefit of the Advanced Manufacturing Production Credit under Section 45X, which is discussed below and favorable changes in the current year regarding our US valuation allowance.
The following table presents the amounts paid for income taxes, net of refunds:
Section 45X of the Inflation Reduction Act of 2022 ("IRA") contains a production tax credit equal to 10% of certain eligible production costs, including, without limitation, labor, energy, depreciation and amortization and overhead expenses. On October 24, 2024, the U.S. Department of the Treasury and the Internal Revenue Service issued final regulations on the production tax credit requirements under Internal Revenue Code Section 45X (the "IRA Regulations"). The IRA Regulations provide guidance on rules that taxpayers must satisfy to qualify for the IRA Section 45X tax credit. For the year ended December 31, 2025 and December 31, 2024, we recognized $89.1 million and $89.7 million as a reduction in Cost of goods sold, and $3.8 million and $2.9 million as a reduction in selling, general and administrative expenses, respectively, within the Consolidated Statements of Operations. In July 2025, the One Big Beautiful Bill Act (the "Act") became law. The Act removed the exemption for critical minerals related to the phase out of the advanced manufacturing production tax credit under Internal Revenue Code Section 45X of the Inflation Reduction Act of 2022 and final regulations issued in October of 2024. Under the Act, beginning in 2031, the amount of the tax credit will be reduced by 25% each year and reduced to 0% in 2034. Additionally, the Act made changes to, but not limited to, permanently extending bonus depreciation that permits full expensing of qualified property, and changes to limitations on the deductibility of interest expense. The Act did not have a material impact on our financial results for the year ending December 31, 2025. We will continue to evaluate the effects of the Act on our results as further guidance is issued. The Company’s accounting policy with respect to releasing income tax effects from accumulated other comprehensive income is to apply a security by security approach whereby the tax effects are measured based on the change in the unrealized gains or losses reflected in Other comprehensive income (loss). Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of our deferred tax assets and liabilities as of December 31 are as follows:
We regularly assess the likelihood that deferred tax assets will be recovered from future taxable income. To the extent we believe that it is more likely than not that a deferred tax asset will not be realized, a valuation allowance is established. When a valuation allowance is established or increased, an income tax charge is included in the Consolidated Statements of Operations and net deferred tax assets are adjusted accordingly. Future changes in tax laws, statutory tax rates and taxable income levels could result in actual realization of the deferred tax assets being materially different from the amounts provided for in the consolidated financial statements. If the actual recovery amount of the deferred tax asset is less than anticipated, we would be required to write-off the remaining deferred tax asset and increase the tax provision. We have a valuation allowance of $471.0 million recorded against our net U.S. and Jamaican deferred tax assets, and a portion of our Icelandic deferred tax assets as of December 31, 2025. The Company is subject to the provisions of ASC 740-10, Income Taxes, which requires that the effect on deferred tax assets and liabilities of a change in tax rates be recognized in the period the tax rate change was enacted. The changes in the valuation allowance are as follows:
The significant components of our NOLs are as follows:
(1)US federal NOLs begin to expire in 2028. (2)US state NOLs begin to expire in 2027. (3)NOLs in Iceland expire in 2026 and 2035. (4)NOLs in Jamaica do not expire. Our ability to utilize our deferred tax assets to offset future federal taxable income may be significantly limited if we experience an "ownership change" as defined in the Code. In general, an ownership change would occur if our "five-percent shareholders," as defined under the Code, collectively increase their ownership in us by more than 50 percentage points over a rolling three-year period. Future transactions in our stock that may not be in our control may cause us to experience such an ownership change and thus limit our ability to utilize net operating losses, tax credits and other tax assets to offset future taxable income. A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits (excluding interest) is as follows:
As of December 31, 2025, the Company’s gross unrecognized tax benefits totaled $3.6 million. Included in the above balances are tax positions relating to temporary differences where there is uncertainty about the timing of tax return inclusion, but not that the amounts will ultimately be tax deductible. Because of the impact of deferred tax accounting, other than interest and penalties, the timing would not impact the annual effective tax rate but could accelerate the payment of cash to the taxing authority to an earlier period. It is our policy to recognize potential accrued interest and penalties related to unrecognized tax benefits in income tax expense. The Company considers the undistributed earnings of its foreign subsidiaries and joint ventures to be permanently reinvested and has not provided for U.S. federal income taxes on these unremitted earnings. No deferred tax liability has been recorded for the related outside basis differences in these entities. Determination of the amount of any unrecognized deferred tax liability on this outside basis difference is not practicable as such determination involves material uncertainties about the potential extent and timing of any reversals. Century and its subsidiaries file income tax returns in the U.S. federal jurisdiction, various state and local jurisdictions, and several foreign jurisdictions. Our federal income tax returns have been reviewed by the IRS through 2010. However, we have NOLs beginning in 2008 that are available for carryforward to future years. Under U.S. tax law, NOLs may be adjusted by the IRS until the statute of limitations expires for the year in which the NOL is used. Accordingly, our 2008 and later NOLs may be reviewed until they are used or expire. We are subject to examination by tax authorities according to statutory periods defined in each jurisdiction. The earliest statutory period open is beginning in 2020.
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Commitments and Contingencies |
12 Months Ended |
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Dec. 31, 2025 | |
| Commitments and Contingencies Disclosure [Abstract] | |
| Commitments and Contingencies | 17. Commitments and Contingencies We have pending against us or may be subject to various lawsuits, claims and proceedings related primarily to employment, commercial, stockholder, environmental, safety and health matters and are involved in other matters that may give rise to contingent liabilities. While the results of such matters and claims cannot be predicted with certainty, we believe that the ultimate outcome of any such matters and claims will not have a material adverse impact on our financial condition, results of operations or liquidity. However, because of the nature and inherent uncertainties of litigation and estimating liabilities, should the resolution or outcome of these actions be unfavorable, our business, financial condition, results of operations and liquidity could be materially and adversely affected. In evaluating whether to accrue for losses associated with legal or environmental contingencies, it is our policy to take into consideration factors such as the facts and circumstances asserted, our historical experience with contingencies of a similar nature, the likelihood of our prevailing and the severity of any potential loss. For some matters, no accrual is established because we have assessed our risk of loss to be remote. Where the risk of loss is probable and the amount of the loss can be reasonably estimated, we record an accrual, either on an individual basis or with respect to a group of matters involving similar claims, based on the factors set forth above. While we regularly review the status of, and our estimates of potential liability associated with, contingencies to determine the adequacy of any associated accruals and related disclosures, the ultimate amount of loss may differ from our estimates. Legal Contingencies Ravenswood Retiree Medical Benefits changes In November 2009, Century Aluminum of West Virginia ("CAWV") filed a class action complaint for declaratory judgment against the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USW"), the USW’s local and certain CAWV retirees, individually and as class representatives ("CAWV Retirees"), seeking a declaration of CAWV’s rights to modify/terminate retiree medical benefits. Later in November 2009, the USW and representatives of a retiree class filed a separate suit against CAWV, Century Aluminum Company, Century Aluminum Master Welfare Benefit Plan, and various John Does with respect to the foregoing. On August 18, 2017, the District Court for the Southern District of West Virginia approved a settlement agreement in respect of these actions, pursuant to the agreement, CAWV agreed to make payments into a trust for the benefit of the CAWV Retirees in the aggregate amount of $23.0 million over the course of 10 years. Upon approval of the settlement, we paid $5.0 million to the aforementioned trust in September 2017 and recognized a gain of $5.5 million to arrive at the-then net present value of $12.5 million. CAWV has agreed to pay the remaining amounts under the settlement agreement in annual increments of $2.0 million for nine years. As of December 31, 2025, $1.9 million was recorded in other current liabilities, representing the current accrual of the final payment. PBGC Settlement In 2013, we entered into a settlement agreement with the Pension Benefit Guarantee Corporation ("the PBGC") regarding an alleged "cessation of operations" at our Ravenswood facility (the "PBGC Settlement Agreement"). Pursuant to the terms of the PBGC Settlement Agreement, we agreed to make additional contributions (above any minimum required contributions) to our defined benefit pension plans totaling approximately $17.4 million. Under certain circumstances, in periods of lower primary aluminum prices relative to our cost of operations, we were able to defer one or more of these payments, provided that we provide the PBGC with acceptable security for such deferred payments. We historically elected to defer certain payments under the PBGC Settlement Agreement and provided the PBGC with the appropriate security. On October 1, 2021, we amended the PBGC Settlement Agreement (the "Amended PBGC Settlement Agreement") such that we removed the deferral mechanism and agreed to contribute approximately $2.4 million per year to our defined benefit pension plans for a total of approximately $9.6 million, over four years beginning on November 30, 2022 and ending on November 30, 2025, subject to acceleration if certain terms and conditions are met in such amendment. As of December 31, 2025, we have made all contributions under the Amended PBGC Settlement Agreement. Sebree Sebree has a power supply arrangement with Kenergy and Century Marketer LLC (“Century Marketer"), Century's wholly-owned subsidiary that acts as a Midcontinent Independent System Operator ("MISO") market participant. Under this arrangement, Sebree gets access to power at MISO pricing plus transmission and other costs. As the MISO Market Participant, Century Marketer purchases power from MISO for resale to Kenergy, which then resells the power to Sebree. Century Marketer's power supply arrangement with Kenergy has an effective term through May 31, 2028, with automatic one-year extensions unless either party provides one-year notice of termination prior to the May 31 anniversary date. Similarly, Kenergy's power supply contract with Sebree has a term through December 31, 2026, with automatic one-year extensions unless either party provides one-year notice of termination prior to the December 31 anniversary date. Mt. Holly Century Aluminum of South Carolina, Inc. ("CASC") has a power supply agreement with South Carolina Public Service Authority (“Santee Cooper”) that has an effective term through December 2031. Under this power supply agreement, 100% of Mt. Holly’s electrical power requirements are supplied from Santee Cooper’s generation at cost of service based rates. Grundartangi Grundartangi has power purchase agreements for approximately 545 MW with HS Orka hf ("HS"), Landsvirkjun and Orkuveita Reykjavikur ("OR"). These power purchase agreements expire on various dates from 2026 through 2036 (subject to extension). The power purchase agreements with each of HS and OR provide power at LME-based variable rates for the duration of these agreements. The larger Landsvirkjun agreement provides for fixed rate with an additional variable rate linked to the LME. Grundartangi also has a separate 25 MW power purchase agreement with Landsvirkjun at an LME-based variable rate. Other Commitments and Contingencies Labor Commitments The bargaining unit employees at our Grundartangi, Vlissingen, Hawesville, Sebree and Jamalco facilities are represented by labor unions, representing approximately 55% of our total workforce. Approximately 84% of Grundartangi’s work force is represented by five labor unions, governed by a labor agreement that establishes wages and work rules for covered employees. This agreement is effective through December 31, 2029. 100% of Vlissingen’s workforce is represented by the Federation for the Metal and Electrical Industry ("FME"), a Netherlands' employers' organization for companies in the metal, electronics, electrical engineering and plastic sectors. The FME negotiates working conditions with trade unions on behalf of its members, which, when agreed upon, are then applicable to all employees of Vlissingen. The current labor agreement is effective through December 31, 2026. Approximately 36% of our U.S. based work force is represented by the Allied Industrial and Service Workers International Union ("USW") through separately negotiated labor agreements for each facility. The labor agreement for Hawesville employees was effective through April 1, 2026, but was terminated early on February 13, 2026. Mt. Holly employees are not represented by a labor union. Century Sebree's labor agreement with the USW for its employees is effective through October 28, 2028. Approximately 62% of Jamalco's work force is represented by the Union of Technical, Administrative, and Supervisory Personnel ("UTASP") through separately labor agreements for hourly and salaried employee groups. Both contracts were effective through December 31, 2023. Jamalco is currently in the process of negotiating new contracts with both the salaried and hourly employee groups. Until new contracts are reached, employees will continue to operate under the current agreements. Contingent Obligation We have a contingent obligation in connection with the “unwind” of a contractual arrangement between CAKY, Big Rivers Electric Corporation ("Big Rivers") and a third party and the execution of a long-term cost-based power contract with Kenergy, a member of a cooperative of Big Rivers, in July 2009. This contingent obligation consists of the aggregate payments made to Big Rivers by the third party on CAKY’s behalf in excess of the agreed upon base amount under the long-term cost-based power contract with Kenergy. As of December 31, 2025, the principal and accrued interest for the contingent obligation was $33.7 million, which was fully offset by a derivative asset. We may be required to make installment payments for the contingent obligation in the future. These payments are contingent based on the LME price of primary aluminum and the level of Hawesville’s operations. Interest accrues at an annual rate equal to 10.94%. As of December 31, 2025, the LME forward market prices exceed the threshold for payment. In addition, based on the fact that we recently sold the Hawesville property, which is to be developed into a data center, we believe that we will not be required to make payments on the contingent obligation during the term of the agreement, which expires in 2028. There can be no assurance that circumstances will not change thus accelerating the timing of such payments.
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Asset Retirement Obligations |
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| Asset Retirement Obligation Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Asset Retirement Obligations | 18. Asset Retirement Obligations The reconciliation of the changes in our AROs is presented below:
(1) Current portion of asset retirement obligations is recorded in Accrued and other current liabilities.
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Business Segments |
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| Segment Reporting [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Business Segments | 19. Business Segments The Company is a producer of primary aluminum and alumina. The Company has organized itself, including management personnel and systems, financial processes, operational execution, governance and risk oversight, regulatory compliance, and every other aspect of the Company’s operations, to assess and manage the business on a holistic basis, from mine to metal, which tracks the upstream manufacturing process for aluminum. To better reflect this operational and organizational approach, and to further enhance the reporting of its financial and operating results, beginning with the quarter ended March 31, 2025, the Company’s Chief Executive Officer and Chief Operating Decision Maker ("CODM") regularly receives and reviews financial information at the consolidated level to evaluate business performance and make operating decisions. The CODM uses the U.S. GAAP measure of consolidated Net Income to develop forecasting, to evaluate the Company’s overall profitability and financial performance and to make key operating decisions, such as the allocation of resources. Given the change described above, the Company has determined that neither its three smelters nor Jamalco’s mining and refining operations meet the definition of operating segments. As a result, the Company has determined that the Company has only one operating and only one reportable segment, and it is managed on a consolidated basis. In accordance with ASC 280-10-50-34, the corresponding information for earlier periods is recast in the tables below to conform with the updated presentation. Segment assets are reported on our Consolidated Balance Sheets as Total assets. Our Consolidated Statements of Cash Flows presents Depreciation, depletion and amortization expense and includes the measure of Capital expenditures. The following table presents information about the Company's single segment for the years ended December 31, .
(1)A component of Cost of goods sold. (2)Includes raw materials, labor, energy, freight costs, FIFO inventory adjustments and other direct cost of goods sold. (3)Advanced production credit related to Section 45X of the IRA. (4)Includes inventory revaluation to lower of cost or net realizable value and changes in inventory reserve. (5)Represents the depreciation expenses and expenses related to leased assets that are directly related to the cost of goods sold. Long-lived Assets
(1)Includes long-lived assets other than financial instruments and deferred taxes. Major customer information Revenues from Glencore in 2025, 2024 and 2023 exceeded 10% of our net sales. See Note 4. Related Party Transactions for additional information on sales to Glencore.
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Derivatives |
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| Derivative Instruments and Hedging Activities Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivatives | 20. Derivatives As of December 31, 2025, we had an open position of 48,400 tonnes related to LME forward financial sales contracts to fix the forward LME aluminum price. These contracts are expected to settle monthly through June 2027. We had an open position of 89,800 tonnes related to MWP forward financial sales contracts to fix the forward MWP price. These contracts are expected to settle monthly through December 2027. We also enter into financial contracts with various counterparties to offset fixed price sales arrangements with certain of our customers ("fixed for floating swaps") to remain exposed to the LME and MWP aluminum prices. As of December 31, 2025, we had no open fixed for floating swaps. We have entered into financial contracts to hedge a portion of our Jamalco fuel cost exposure ("HFO price swaps"). The volume of heavy fuel oil ("HFO") consumed at Jamalco is measured per barrel and as of December 31, 2025, we had an open position of 225,000 barrels. The HFO price swaps are expected to settle monthly through October 2026. We have entered into financial contracts to fix a portion of our exposure to the Indiana Hub power market at our Sebree plant ("Indiana Hub power price swaps"). As of December 31, 2025, we had an open position of 884,712 MWh. The Indiana Hub power price swaps are expected to settle monthly through June 2027. Our agreements with derivative counterparties contain certain provisions requiring collateral to be posted in the event the market value of our position exceeds the margin threshold limit of our master agreement with the counterparty. As of December 31, 2025 and December 31, 2024, the Company had no recorded restricted cash as collateral related to open derivative contracts under the master arrangements with our counterparties. The following table sets forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of December 31, 2025 and 2024, respectively:
(1)Commodity contracts reflect our outstanding LME and MWP forward financial sales contracts, fixed for floating swaps, HFO price swaps and Indiana Hub power price swaps. At December 31, 2025 and December 31, 2024, there were no commodity contracts with Glencore. (2)Foreign exchange contracts reflect our outstanding FX swaps and casthouse currency hedges. The following table summarizes the net gain (loss) on forward and derivative contracts for the years ended December 31, 2025, 2024, and 2023:
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| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Variable Interest Entity | 21. Variable Interest Entity The Company consolidates Jamalco, a bauxite mining and alumina refinery in Jamaica, under the variable interest entity ("VIE") model. Jamalco lacks sufficient equity investment at risk in accordance with relevant guidance. Based on its purpose and design, Jamalco is expected to require additional subordinated financial support, such as those in the form of equity contributions or other forms of subordinated financing, which the Company expects would require parent guarantees. The Company owns a 55% ownership interest in Jamalco through its wholly-owned subsidiary, GAJL, which serves as the managing partner. The Company is responsible for funding 55% of Jamalco's operating costs and capital requirements and is not obligated to provide additional financial support beyond its equity interest. Upon acquisition, the Company made an immediate equity contribution to Jamalco and has provided subsequent financing of costs for Jamalco to perform its activities in the ordinary course of business. The Company obtains direct ownership of our 55% share of Jamalco’s outputs and purchases the remaining 45% of the output from the Government of Jamaica. Through direct ownership and purchase, 100% of Jamalco’s output is either retained and utilized in the Company’s business operations or sold by the Company. The Company’s consolidated statement of cash flows reflects 100% of cash flows related to the Jamalco operations. The Company receives cash proceeds from the Government of Jamaica for its 45% interest of the Jamalco operating costs and capital requirements. Although our partner has certain participating rights over some decisions of the entity, the Company has power over the majority of key activities at Jamalco that significantly affect its economic performance over which the counterparty does not have such participating rights; therefore, the Company is the primary beneficiary of the VIE. The table below shows the carrying amounts and classification of the consolidated VIE's assets and liabilities included in the Consolidated Balance Sheets as of December 31, 2025 and 2024.
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Restatement of Previously Issued Financial Statements |
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Restatement of Previously Issued Financial Statements | 22. Restatement of Previously Issued Financial Statements Subsequent to the issuance of our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, the Company identified an error in accounting in its historical financial statements related to the consolidation of its Jamalco joint venture whereby the Company previously used the proportionate method of consolidation for certain of Jamalco's net assets versus the full consolidation method. The Company has corrected the error in the Consolidated Financial Statements as of and for the periods ended December 31, 2024 and December 31, 2023 presented herein. Revisions to the Company’s previously reported disclosures have been reflected in Note 1. Summary of Significant Accounting Policies; Note 2. Acquisition of Jamalco; Note 11. Property, Plant and Equipment; Note 13. Pension and Other Postretirement Benefits; Note 18. Asset Retirement Obligations; Note 19. Business Segments; and Note 21. Variable Interest Entity. A summary of the revisions to the Company’s previously reported financial statements is provided in this Note 22. Restatement of Previously Issued Financial Statements and Note 23. Revisions to Prior Period Quarterly Consolidated Financial Statements (unaudited). The effects of the corrections described above on the Company’s Consolidated Statements of Operations were as follows:
The effects of the corrections described above on the Company's Consolidated Statements of Comprehensive Income (Loss) were as follows:
The effects of the corrections described above on the Company's Consolidated Balance Sheets were as follows:
The effects of the corrections described above on the Company’s Consolidated Statements of Cash Flows were as follows:
The effects of the corrections described above on the Company's Consolidated Statements of Shareholder's Equity were as follows:
The Company has also restated impacted amounts within the accompanying footnotes to the Consolidated Financial Statements.
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Quarterly Financial Information (Unaudited and Restated) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Quarterly Financial Information Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Quarterly Financial Information (Unaudited and Restated) | 23. Quarterly Financial Information (Unaudited and Restated) As further discussed in Note 1. Summary of Significant Accounting Policies and Note 22. Restatement of Previously Issued Financial Statements, the Company determined that corrections to the unaudited condensed consolidated financial statements were required for all impacted periods previously included in each of the Company's Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2025, June 30, 2025, September 30, 2025, March 31, 2024, June 30, 2024, and September 30, 2024. Restated amounts are computed independently for each quarter presented; therefore, the sum of the quarterly amounts may not equal the total amount for the year due to rounding. The restatement impacts to the Company's consolidated statements of operations were as shown below.
The restatement impacts to the Company's consolidated balance statements were as shown below (dollars in millions).
The restatement impacts to the Company's consolidated statements of shareholders' equity as shown below (dollars in millions).
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Subsequent Events |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Subsequent Events [Abstract] | |
| Subsequent Events | 24. Subsequent Events New Smelter Project On January 26, 2026, we announced that we had entered into a joint development agreement with Emirates Global Aluminium (“EGA”) to build the first new primary aluminum smelter in the United States since our Mt. Holly facility came online in 1980. Under the joint development agreement, EGA will own 60 percent of the joint venture, with Century Aluminum owning the remaining 40 percent. The new plant, to be built in Inola, Oklahoma, is expected to produce 750,000 tonnes of aluminum per year, more than doubling current U.S. production. Construction of the project is expected to start by the end of 2026, with detailed engineering work already and negotiations with Public Service Company of Oklahoma and the state of Oklahoma on a competitive long-term power supply underway. Sale of Hawesville On February 2, 2026, we completed the sale of our Hawesville, Kentucky facility to an affiliate of Terawulf, Inc. for $200.0 million in cash and a 6.8% non-dilutive minority equity interest in the Terawulf affiliate that intends to develop and own a high-performance computing/artificial intelligence data center on the site. A large portion of the proceeds are intended to be deployed to expand our domestic primary aluminum production capacity through the restart of the last potline at our Mt. Holly facility and investments in our new smelter project. In connection with our sale of the Hawesville facility, on February 2, 2026, we terminated the letter of credit in the amount of $8.1 million under our U.S. Credit Facility, effectively prepaying the IRBs. As noted throughout this Form 10-K, on February 13, 2026, we terminated our labor agreement with United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USW") for former employees at our Hawesville facility, the impacts for which are disclosed herein.
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Insider Trading Arrangements |
3 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Trading Arrangements, by Individual | |
| Rule 10b5-1 Arrangement Adopted | false |
| Non-Rule 10b5-1 Arrangement Adopted | false |
| Rule 10b5-1 Arrangement Terminated | false |
| Non-Rule 10b5-1 Arrangement Terminated | false |
Insider Trading Policies and Procedures |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Insider Trading Policies and Procedures [Line Items] | |
| Insider Trading Policies and Procedures Adopted | true |
Cybersecurity Risk Management and Strategy Disclosure |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| Cybersecurity Risk Management, Strategy, and Governance [Line Items] | |
| Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block] | Century recognizes the importance of developing, implementing, and maintaining appropriate cybersecurity measures to safeguard our information systems and protect the confidentiality, integrity, and availability of our data. The Board is actively involved in oversight of Century’s risk management program, and cybersecurity represents an important component of Century’s overall approach to enterprise risk management (“ERM”). Century’s cybersecurity policies, standards, processes and practices are based on recognized security frameworks and applicable industry standards. In general, Century seeks to address cybersecurity risks through a comprehensive approach that is focused on preserving the confidentiality, security and availability of the information that Century generates, collects and stores by identifying, preventing and mitigating cybersecurity threats and effectively responding to cybersecurity incidents when they occur. As one of the critical elements of the Company’s overall ERM approach, the Company’s cybersecurity program is focused on the following key areas: •Governance: As discussed in more detail under the heading “Governance,” the Board’s oversight of cybersecurity risk management is supported by the Company’s Chief Information Officer, other members of Management and a dedicated Cybersecurity team. •Collaborative Approach: The Company has implemented a comprehensive approach to identifying, preventing and mitigating cybersecurity threats and incidents, while also implementing controls and procedures that provide for the prompt escalation of certain cybersecurity incidents so that decisions regarding the public disclosure and reporting of such incidents can be made by management in a timely manner. •Technical Safeguards: The Company deploys technical safeguards that are designed to protect the Company’s information systems from cybersecurity threats, including firewalls, intrusion prevention and detection systems, logical access controls, and endpoint protection, which are evaluated and improved through vulnerability assessments and cybersecurity threat intelligence. •Incident Response and Recovery Planning: The Company has established and maintains incident response and recovery plans that address the Company’s response to a cybersecurity incident. •Third-Party Risk Management: The Company maintains a risk-based approach to identifying and overseeing cybersecurity risks presented by third parties, including vendors, service providers and other external users of the Company’s systems, as well as the systems of third parties that could adversely impact our business in the event of a cybersecurity incident affecting those third-party systems. •Network Penetration Testing: The Company performs an internal and external network penetration test led by its Internal Audit team and addresses any findings in a timely manner.
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| Cybersecurity Risk Management Processes Integrated [Flag] | true |
| Cybersecurity Risk Management Processes Integrated [Text Block] | Century recognizes the importance of developing, implementing, and maintaining appropriate cybersecurity measures to safeguard our information systems and protect the confidentiality, integrity, and availability of our data. The Board is actively involved in oversight of Century’s risk management program, and cybersecurity represents an important component of Century’s overall approach to enterprise risk management (“ERM”). Century’s cybersecurity policies, standards, processes and practices are based on recognized security frameworks and applicable industry standards. In general, Century seeks to address cybersecurity risks through a comprehensive approach that is focused on preserving the confidentiality, security and availability of the information that Century generates, collects and stores by identifying, preventing and mitigating cybersecurity threats and effectively responding to cybersecurity incidents when they occur.
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| Cybersecurity Risk Management Third Party Engaged [Flag] | true |
| Cybersecurity Risk Third Party Oversight and Identification Processes [Flag] | true |
| Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag] | false |
| Cybersecurity Risk Board of Directors Oversight [Text Block] | The Board as a whole also oversees the Company’s cybersecurity risks. Our Chief Information Officer updates the Board periodically regarding the actions management is taking to mitigate the Company’s cybersecurity risks and enhance the Company’s cybersecurity protection. Management routinely evaluates the Company’s existing security processes, procedures and systems in order to determine whether additional enhancements are needed to further reduce the likelihood and impact of a future cybersecurity event. Some of the Company’s current safeguards include multi-factor authentication for remote access to systems; performing email phishing test campaigns; email spam filtering; restricted internet firewall rules; limiting memory stick and external hard drive use; requiring timely application of security and software patches on servers; antivirus endpoint protection; performing 24-hour/7-day a week network monitoring; and improving our backup and recovery strategy, among others.
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| Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block] | The Chief Information Officer, as well as other members of Management, plays a pivotal role in informing the Board on cybersecurity risks by providing comprehensive briefings to the Board on a regular basis. |
| Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block] | The Chief Information Officer, as well as other members of Management, plays a pivotal role in informing the Board on cybersecurity risks by providing comprehensive briefings to the Board on a regular basis. These briefings encompass a broad range of topics, including: •Current cybersecurity landscape and emerging threats; •Status of ongoing cybersecurity initiatives and strategies; •Overall security posture and layers of defense; •Incident reports and learnings from any cybersecurity events; and •Compliance with regulatory requirements and industry standards. In addition to regularly scheduled meetings, the Board and the Chief Information Officer maintain an ongoing dialogue regarding emerging or potential cybersecurity risks.
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| Cybersecurity Risk Role of Management [Text Block] | The Chief Information Officer, as well as other members of Management, plays a pivotal role in informing the Board on cybersecurity risks by providing comprehensive briefings to the Board on a regular basis. These briefings encompass a broad range of topics, including: •Current cybersecurity landscape and emerging threats; •Status of ongoing cybersecurity initiatives and strategies; •Overall security posture and layers of defense; •Incident reports and learnings from any cybersecurity events; and •Compliance with regulatory requirements and industry standards. In addition to regularly scheduled meetings, the Board and the Chief Information Officer maintain an ongoing dialogue regarding emerging or potential cybersecurity risks. Together, they receive updates on any significant developments in the cybersecurity domain, ensuring the Board’s oversight is proactive and responsive. The Board actively participates in strategic decisions related to cybersecurity, offering guidance and approval for major initiatives. This involvement ensures that cybersecurity considerations are integrated into the broader strategic objectives of the Company. The Board conducts an annual review of the company’s cybersecurity posture and the effectiveness of its risk management strategies. This review helps in identifying areas for improvement and ensuring the alignment of cybersecurity efforts with the overall risk management framework.
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| Cybersecurity Risk Management Positions or Committees Responsible [Flag] | true |
| Cybersecurity Risk Management Positions or Committees Responsible [Text Block] | The Chief Information Officer, as well as other members of Management, plays a pivotal role in informing the Board on cybersecurity risks by providing comprehensive briefings to the Board on a regular basis. |
| Cybersecurity Risk Management Expertise of Management Responsible [Text Block] | The Chief Information Officer has extensive experience working in and leading the Company's information systems. |
| Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block] | The Chief Information Officer is continually informed about the latest developments in cybersecurity, including potential threats and innovative risk management techniques. This ongoing knowledge acquisition is crucial for the effective prevention, detection, mitigation, and remediation of cybersecurity incidents. The Chief Information Officer implements and oversees processes for the regular monitoring of our information systems. This includes the deployment of advanced security measures and regular system audits to identify potential vulnerabilities. In the event of a cybersecurity incident, the CIO is equipped with a well-defined incident response plan. This plan includes immediate actions to mitigate the impact and long-term strategies for remediation and prevention of future incidents.
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| Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag] | true |
Summary of Significant Accounting Policies (Policies) |
12 Months Ended |
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Dec. 31, 2025 | |
| Accounting Policies [Abstract] | |
| Basis of Presentation | Basis of Presentation — The consolidated financial statements include the accounts of Century Aluminum Company and our subsidiaries, after elimination of all intercompany transactions and accounts. |
| Variable Interest Entities | Variable Interest Entities - We evaluate arrangements and contracts with other entities to determine if they are VIEs and if we are the primary beneficiary. U.S. GAAP provides a framework for identifying VIEs and determining when a company should include the assets, liabilities, non-controlling interest, and results of activities of a VIE in its consolidated financial statements. A VIE should be consolidated if a party with an ownership, contractual or other financial interest in the VIE (a variable interest holder) has the power to direct the VIE’s most significant activities and the obligation to absorb losses or right to receive benefits of the VIE that could be significant to the VIE. A variable interest holder that consolidates the VIE is called the primary beneficiary. Upon consolidation, the primary beneficiary generally must initially record all of the VIE’s assets, liabilities, and non-controlling interests at fair value and subsequently account for the VIE as if it were consolidated. Our evaluation of whether our interest qualifies as the primary beneficiary of a VIE involves significant judgments, estimates and assumptions and includes a qualitative analysis of the activities that most significantly impact the VIE’s economic performance and whether the Company has the power to direct those activities, the design of the entity, the rights of the parties and the purpose of the arrangement. Jamalco is a VIE. See Note 21. Variable Interest Entity.
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| Revenue | Revenue recognition — See Note 5. Revenue. We enter into contracts to sell mainly primary aluminum to our customers. Revenue is recognized when our performance obligations with our customers are satisfied. Our obligations under the contracts are satisfied when we transfer control of our primary aluminum or alumina to our customers which is generally upon shipment or delivery to customer directed locations. The amount of consideration we receive, thus the revenue we recognize, is a function of volume delivered, market price of primary aluminum, which is based on the LME, plus regional premiums and any value-added product premiums or alumina which is based on the alumina pricing index, plus Atlantic differential. The payment terms and conditions in our contracts vary and are not significant to our revenue. We complete an appropriate credit evaluation for each customer at contract inception. Customer payments are due in arrears and are recognized as Accounts receivable - net and due from affiliates in our Consolidated Balance Sheets. In connection with our sales agreements with certain customers, including Glencore, we invoice the customer prior to physical shipment of goods for a majority of production generated from each of our U.S. domestic smelters. For those sales, revenue is recognized only when the customer has specifically requested such treatment and has made a commitment to purchase the product. The goods must be complete, ready for shipment and separated from other inventory with control over the goods passing to the customer. We must retain no further performance obligations.
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| Cash and Cash Equivalents | Cash and Cash Equivalents — Cash and cash equivalents are comprised of cash, money market funds and short-term investments having original maturities of three months or less. The carrying amount of cash equivalents approximates fair value.
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| Accounts Receivable and Due from Affiliates | Accounts Receivable and Due from Affiliates — These amounts are net of an immaterial allowance for expected losses.
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| Inventories | Inventories — Our inventories are stated at the lower of cost or net realizable value, using the first-in, first-out ("FIFO") and the weighted average cost method. Due to the nature of our business, our inventory values are subject to market price changes and these changes can have a significant impact on Cost of goods sold and Gross profit in any period. Reductions in net realizable value below cost basis at the end of a period will have an impact on our Cost of goods sold as this inventory is sold in subsequent periods.
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| Property, Plant and Equipment | Property, Plant and Equipment — Property, plant and equipment is stated at cost. Additions and improvements are capitalized when each asset is placed into service. Asset and accumulated depreciation accounts are relieved for dispositions with resulting gains or losses included in Other expense - net. Maintenance and repairs are expensed as incurred. Depreciation of plant and equipment is provided for by the straight-line method over the following estimated useful lives: Building and improvements 10 to 45 years Machinery and equipment 5 to 35 years Technology and software 3 to 7 years The Company incurs deferred costs during the development stage of a mine life cycle. Such costs include the construction of access and haul roads, detailed drilling and geological analysis to further define the grade and quality of the known bauxite, and overburden removal costs. These costs relate to sections of the related mines where the Company is currently extracting bauxite or preparing for production in the near term. These sections are outlined and planned incrementally and generally are mined over periods outlined in the Company's mine plans. The amount of geological drilling and testing necessary to determine the economic viability of the bauxite deposit being mined is such that the resources are considered to be proved mineral reserves. Mineral reserves are amortized on a units-of-production basis.
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| Impairment of long-lived assets | Impairment of long-lived assets — The Company reviews property, plant and equipment and right of use assets ("long-lived assets") for impairment whenever events or changes in circumstances, known as triggering events, indicate that the carrying amount of a long-lived asset or an asset group may not be recoverable. Management considers various factors when determining if long-lived assets should be evaluated for impairment, including a significant adverse change in the business climate or industry conditions (such as sustained decreases in commodity prices, volatility in energy costs, and the global economy), a current period operating or cash flow loss combined with a history of losses, a significant adverse change in the extent or manner in which an asset is used or a current expectation that the asset will be sold or otherwise disposed of before the end of its useful life. If a triggering event is identified, the Company determines if the long-lived asset or asset group is recoverable. Recoverability is measured by comparison of the carrying amount of a long-lived asset or asset group held and used to estimate undiscounted future net cash flows expected to be generated by the long-lived asset or asset group. Impairment evaluation and fair value is based on estimates and assumptions that take into account our business plans and a long-term investment horizon, including consideration of commodity pricing, energy costs and other global economic conditions which may have an adverse effect on recoverability. If deemed unrecoverable, an impairment loss would be recognized for the amount by which the carrying amount exceeds the estimated fair value of the long-lived asset or asset group.
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| Leases | Leases — We enter into operating lease contracts, as assessed at the inception of the arrangement, for real estate, automobiles, and mobile equipment. We use our incremental borrowing rate as the basis for the discount rate used to calculate the right of use asset ("ROUA") and lease liability. The incremental borrowing rate is determined on a lease-by-lease basis. The terms of our leases vary, including the lease term and the ability to renew or extend certain leases. As part of determining the lease term and potential extensions for purposes of calculating the ROUA and lease liability, we consider our historical practices related to renewal of certain leases. We have made a policy election not to separate lease and non-lease components within contracts. We have also elected not to recognize the impact of short term leases in the ROUA and lease liability balances. Short term leases are leases that have a lease term less than one year and do not include a purchase option.
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| Income Taxes | Income Taxes — We account for income taxes using the asset and liability method, whereby deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. In evaluating our ability to realize deferred tax assets, we use judgment to determine if it is more likely than not that some portion or all of a deferred tax asset will not be realized, and if a corresponding valuation allowance is required.
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| Defined Benefit Pension and Other Postretirement Benefits | Defined Benefit Pension and Other Postretirement Benefits — We sponsor defined benefit pension and Other Postretirement Benefit ("OPEB") plans for certain of our domestic hourly and salaried employees and a supplemental executive retirement benefit plan for certain current and former executive officers. Plan assets and obligations are measured annually or more frequently if there is a re-measurement event, based on the Company’s measurement date utilizing various actuarial assumptions. We attribute the service costs for the plans over the working lives of plan participants. The effects of actual results differing from our assumptions and the effects of changing assumptions are considered actuarial gains or losses. Actuarial gains or losses are recorded in Accumulated other comprehensive income (loss). Net periodic benefit cost is a component of Cost of goods sold; Selling, general and administrative expenses and Other expense - net. We contribute to our defined benefit pension plans based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements.
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| Postemployment Benefits | Postemployment Benefits — We provide certain postemployment benefits to certain former and inactive employees and their dependents during the period following employment but before retirement. These benefits include salary continuance, supplemental unemployment and disability health care. We recognize the estimated future cost of providing postemployment benefits on an accrual basis over the active service life of the employee. Net periodic benefit cost is a component of Cost of goods sold; Selling, general and administrative expenses and Other expense - net.
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| Derivatives and Hedging | Derivatives and Hedging — As a global producer of primary aluminum, our operating results and cash flows from operations are subject to risk of fluctuations in the market prices of primary aluminum. We may from time to time enter into financial contracts to manage our exposure to such risk. Derivative instruments may consist of variable to fixed financial contracts and back-to-back fixed to floating arrangements for a portion of our sale of primary aluminum, where we receive fixed and pay floating prices from our customers and to counterparties, respectively. From time to time, we may manage our exposure to fluctuations in the market price of power through financial instruments designed to protect our downside risk exposure. We are also exposed to foreign currency risk, and we may manage our exposure by entering into foreign currency forward contracts or option contracts for forecasted transactions and projected cash flows for foreign currencies in future periods. Our derivatives are not designated as cash flow hedges. Derivative and hedging instruments are recorded in Derivative assets, Other assets, Derivative liabilities and Derivative liabilities - less current portion in the Consolidated Balance Sheets at fair value. We value our derivative and hedging instruments using quoted market prices and other significant unobservable inputs. We recognize changes in fair value and settlements of derivative instruments in Net (loss) gain on forward and derivative contracts - nonaffiliates and Net gain (loss) on forward and derivative contracts - affiliates in the Consolidated Statements of Operations as they occur.
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| Foreign Currency | Foreign Currency – We are exposed to foreign currency risk due to fluctuations in the value of the U.S. dollar as compared to the Euro and the Icelandic krona ("ISK"), and the Chinese renminbi. Grundartangi, Vlissingen and Jamalco use the U.S. dollar as their functional currency, as contracts for sales of aluminum and alumina and purchases of alumina and power are denominated in U.S. dollars. Transactions denominated in currencies other than the functional currency are recorded based on exchange rates at the time such transactions arise and any transaction gains and losses are reflected in Other expense - net in the Consolidated Statements of Operations. |
| Financial Instruments | Financial Instruments — Receivables, certain life insurance policies, payables, borrowings under revolving credit facilities and debt related to industrial revenue bonds ("IRBs") are carried at amounts that approximate fair value.
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| Earnings per share | Earnings per share — Basic earnings (loss) per share ("EPS") amounts are calculated by dividing Net income (loss) allocated to common stockholders by the weighted average number of common shares outstanding using the two-class method. Diluted EPS is calculated by dividing Net income (loss) allocated to common stockholders by the weighted average number of common and dilutive common equivalent shares outstanding during the period. Dilutive common equivalent shares are calculated using the more dilutive of either the if-converted or two-class methods. Our Series A Convertible Preferred Stock is a non-cumulative perpetual participating convertible preferred stock with no set dividend preferences. In periods where we report net losses, we do not allocate these losses to the Convertible Preferred Stock for the computation of basic or diluted EPS.
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| Asset Retirement Obligations | Asset Retirement Obligations — We are subject to environmental regulations which create certain legal obligations related to the normal operations of our bauxite mine and alumina refinery and our domestic primary aluminum smelter operations. Our asset retirement obligations ("AROs") consist primarily of costs associated with mine reclamation obligations, closure of bauxite residue areas, landfill closure, and the disposal of spent potliner used in the reduction cells of our domestic smelters. AROs are recorded on a discounted basis at the time the obligation is incurred (when the potliner is put in service or upon disturbance of lands to be mined) and accreted over time for the change in the present value of the liability. We capitalize the asset retirement costs by increasing the carrying amount of the related long-lived assets and depreciating these assets over their remaining useful lives. Certain conditional asset retirement obligations ("CAROs") related to the remediation of our primary aluminum facilities for hazardous material, such as landfill materials and asbestos, have not been recorded because they have an indeterminate settlement date. CAROs are a legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within our control.
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| Concentrations of Credit Risk | Concentrations of Credit Risk — Financial instruments, which potentially expose us to concentrations of credit risk, consist principally of trade receivables. Our limited customer base increases our concentrations of credit risk with respect to trade receivables. We routinely assess the financial strength of our customers and collectability of our trade receivables and recognize an allowance based on our estimate of lifetime expected credit losses in accordance with the current expected credit loss model.
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| Share-Based Compensation | Share-Based Compensation — We measure the cost of employee services received in exchange for an award of equity instruments based on the fair value of the award on the grant date. We recognize the cost over the period during which an employee is required to provide service in exchange for the award. We issue shares to satisfy the requirements of our share-based compensation plans. At this time, we do not plan to issue treasury shares to support our share-based compensation plans, but we may in the future. We award performance units to certain officers and employees. The performance units may be settled in cash or common stock at the discretion of the Board. We have not issued any stock options since 2009.
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| Reclassification | Reclassification — Certain amounts in the prior period financial statements have been reclassified to conform to the presentation of the current period financial statements. These immaterial reclassifications had no effect on the previously reported net income or net cash flows.
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| Recent accounting pronouncements | Recent accounting pronouncements In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, that requires presentation of specific categories of reconciling items, as well as reconciling items that meet a quantitative threshold, in the reconciliation between the income tax provision and the income tax provision using statutory tax rates. The standard also requires disclosure of income taxes paid disaggregated by jurisdiction with separate disclosure of income taxes paid to individual jurisdictions that meet a quantitative threshold. The amendments in this accounting standard are effective for fiscal years beginning after December 15, 2024. The Company adopted this guidance for the 2025 annual reporting period on a prospective basis, resulting in additional disclosures within Note 16. Income Taxes. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40m as amended by ASU 2025-01): Disaggregation of Income Statement Expenses, that requires disclosure of the amounts of purchases of inventory, employee compensation, depreciation, and intangible asset amortization included in each relevant expense line item on the income statement. The standard also requires a qualitative description of other amounts included in each relevant expense line item on the income statement that are not separately disclosed. In addition, entities are required to disclose the nature and amount of selling expenses. The new standard is effective for fiscal years beginning after December 15, 2026, and interim periods beginning after December 15, 2027. Early adoption is permitted. We do not expect any impact to the consolidated financial statements, but the standard will require certain additional disclosures in the notes to the consolidated financial statements and the Company plans to adopt this guidance for the annual period ending December 31, 2027. In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities, which adds guidance on the recognition, measurement and presentation of government grants. The new standard is effective for fiscal years beginning after December 15, 2028. Early adoption is permitted. The Company has previously analogized to IAS 20, Accounting for Government Grants and Disclosure of Government Assistance, to account for refundable tax credits as an income grant. The Company's policy on income grants under IAS 20 aligns with the updated guidance, and the Company does not expect a material effect on its consolidated financial statements upon adoption.
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Acquisition of Jamalco (Tables) |
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| Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Fair Value of Assets Acquired and Liabilities Assumed | The following table summarizes the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition:
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| Schedule of Unaudited Pro Forma Financial Information | The following unaudited pro forma financial information reflects the results of operations of the Company for the twelve months ended December 31, 2023 and 2022, respectively, as if the acquisition of Jamalco had been completed on January 1, 2022. This unaudited pro forma financial information has been prepared for informational purposes and is not necessarily indicative of the actual consolidated results of operations had the acquisition been completed on January 1, 2022, nor is the information indicative of future results of operations of the combined companies.
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Related Party Transactions (Tables) |
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| Related Party Transactions [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Related Party Transactions | A summary of the aforementioned significant related party sales and purchases for the years ended December 31, 2025, 2024 and 2023 is as follows:
(1)Includes settlements of financial contract positions.
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Revenue (Table) |
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| Revenue from Contract with Customer [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Disaggregation of Revenue | We disaggregate our revenue by geographical region as follows:
The table below shows the amount of net sales to external customers for each of the Company's product categories which accounted for 10% or more of consolidated net sales in either period for the years ended December 31, 2025, 2024 and 2023.
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Leases (Tables) |
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| Schedule of Assets and Liabilities, Lessee | Our ROUA and lease liability balances for the years ended December 31, 2025 and December 31, 2024 were as follows:
(1)ROUA was recorded as part of Other Assets within non-current assets at December 31, 2025 and 2024. (2)Lease liability - current was recorded as part of Accrued and other current liabilities within current liabilities at December 31, 2025 and 2024. (3)Lease liability - non-current was recorded as part of Other liabilities within non-current liabilities at December 31, 2025 and 2024.
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| Schedule of Maturities of Operating Lease Liability Balances | The undiscounted maturities of our operating lease liability balances as of December 31, 2025 are as follows:
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| Schedule of Lease, Expense | Total operating expense includes the following:
(1)Total lease expense is included in Cost of goods sold and Selling, general, and administrative expenses on the Consolidated Statements of Operations.
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Fair Value Measurements (Tables) |
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value Disclosures [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Financial Assets and Liabilities at Fair Value on a Recurring Basis |
(1)Trust assets are currently invested in money market funds. These trust assets are held to fund the non-qualified supplemental executive pension benefit obligations for certain of our officers.
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| Schedule of Valuation Methodology for Assets and Liabilities at Fair Value | The following section describes the valuation techniques and inputs used for fair value measurements categorized within Level 2 of the fair value hierarchy:
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Debt (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Debt Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Debt |
(1)The IRBs are classified as current liabilities because they are remarketed weekly and could be required to be repaid upon demand if there is a failed remarketing. The interest rate at December 31, 2025 was 3.45%. (2)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.25%. (3)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.23%. (4)We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at December 31, 2025 was 7.56%
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| Schedule of Debt Redemption Rights | Redemption Rights. Prior to August 1, 2028, we may redeem the 2032 Notes, in whole or in part, at a redemption price equal to 100.00% of the principal amount plus a make-whole premium and accrued and unpaid interest, and if redeemed during the twelve-month period beginning on August 1 of the years indicated below, at the following redemption prices plus accrued and unpaid interest:
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| Schedule of Line of Credit Facilities |
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Inventories (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Inventory, Net [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Inventories | Inventories, at December 31, consist of the following:
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Property, Plant and Equipment (Tables) |
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| Property, Plant and Equipment [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Property, Plant and Equipment | Property, plant and equipment, at December 31, consist of the following:
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Accumulated Other Comprehensive Loss ("AOCL") (Tables) |
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Dec. 31, 2025 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Accumulated Other Comprehensive Loss |
(1)The allocation of the income tax effect to the components of other comprehensive loss is as follows:
The following table summarizes the changes in the accumulated balances for each component of AOCL:
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| Schedule of Reclassification out of AOCL | Reclassifications out of AOCL were included in the Consolidated Statements of Operations as follows:
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Pension and Other Postretirement Benefits (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Retirement Benefits [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Changes in Projected Benefit Obligations | The change in benefit obligation and change in plan assets as of December 31 are as follows:
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| Schedule of Changes in Fair Value of Plan Assets |
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| Schedule of Amounts Recognized in Balance Sheet |
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| Schedule of Net Benefit Cost | Net Periodic Benefit Cost:
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| Schedule of Amounts Recognized in Accumulated Other Comprehensive Income (Loss) | Other changes in Plan Assets and Benefit Obligations Recognized in Accumulated Other Comprehensive Income (Loss) (pre-tax):
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| Schedule of Weighted Average Assumptions Used in Calculating Benefit Obligation and Net Periodic Benefit Cost | Weighted average assumptions used to determine benefit obligations at December 31:
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
(1)We use the Ryan Above Median Yield Curve to determine the discount rate. (2)For 2025, the rate of compensation increase is 3.2%. For 2024, the rate of compensation increase was 3.5%. For 2023, the rate of compensation increase was 4% per year for the first year and 3.5% per year thereafter. (3)The rate for each of our defined benefit plans was selected by taking into account our expected asset mix and is based on historical performance as well as expected future rates of return on plan assets.
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| Schedule of Allocation of Plan Assets | The Pension Plans’ weighted average long-term strategic asset allocation policy targets are as follows:
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| Defined Benefit Plan, Plan Assets, Category | The following summarizes the Company’s Pension Plans' assets fair value by asset category:
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| Schedule Of Expected Benefit Plan Contributions | We expect to make the following contributions for 2026:
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| Schedule of Expected Benefit Payments | The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
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| Schedule of Multiemployer Plans | Century’s participation in the plan for the year ended December 31, 2025, is outlined in the table below.
(1)The "EIN/Pension Plan Number" column provides the Employee Identification Number (EIN) and the three-digit plan number, if applicable. (2)The most recent Pension Protection Act zone status available in 2025 and 2024 is for the plan's year-end December 31, 2024 and December 31, 2023, respectively. The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the red zone are generally less than 65 percent funded, plans in the yellow zone are less than 80 percent funded, and plans in the green zone are at least 80 percent funded. (3)The “Subject to Financial Improvement / Rehabilitation Plan” column indicates plans for which a financial improvement plan (FIP) or a rehabilitation plan (RP) is either pending or has been implemented. The last column lists the expiration date(s) of the collective-bargaining agreement(s) to which the plans are subject. On February 13, 2026, we terminated our labor agreement with USW for former employees at our Hawesville facility.
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Share-based Compensation (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share-Based Payment Arrangement [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Service-Based Share Awards Activity |
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| Schedule of Share-Based Compensation Expense | The following table summarizes the compensation cost recognized for the years ended December 31, 2025, 2024 and 2023 for all service-based and performance-based share awards. The compensation cost is included as part of Selling, general and administrative expenses and Cost of goods sold in our Consolidated Statements of Operations.
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Earnings Per Share (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Earnings Per Share [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Basic and Diluted Earnings (Loss) Per Share and Securities Excluded from the Calculation of Diluted EPS | The following table shows the basic and diluted EPS for 2025, 2024, and 2023:
(1)In periods when we report a net loss, all share-based compensation awards, convertible preferred shares and convertible senior notes are excluded from the calculation of diluted weighted average shares outstanding because of their anti-dilutive effect on earnings (loss) per share.
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Income Taxes (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income Tax Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Components of Pre-Tax Book Income (Loss) | The components of pre-tax book income (loss) consist of the following:
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| Schedule of Significant Components of the Income Before Income Tax Expense | Significant components of income tax expense consist of the following:
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| Schedule of Reconciliation of the Statutory U.S. Federal Income Tax Rate to the Effective Income Tax Rate on Income (Loss) |
(1)State taxes in Tennessee and Kentucky comprise the majority (greater than 50 percent) of the tax effect in this category.
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| Schedule of Income Tax Paid | The following table presents the amounts paid for income taxes, net of refunds:
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| Schedule of Deferred Tax Assets and Liabilities | The significant components of our deferred tax assets and liabilities as of December 31 are as follows:
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| Schedule of Changes in Valuation Allowance | The changes in the valuation allowance are as follows:
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| Schedule of Significant Components of Net Operating Loss Carryforwards | The significant components of our NOLs are as follows:
(1)US federal NOLs begin to expire in 2028. (2)US state NOLs begin to expire in 2027. (3)NOLs in Iceland expire in 2026 and 2035. (4)NOLs in Jamaica do not expire.
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| Schedule of Reconciliation of Gross Unrecognized Tax Benefits | A reconciliation of the beginning and ending amounts of gross unrecognized tax benefits (excluding interest) is as follows:
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Asset Retirement Obligations (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Asset Retirement Obligation Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Changes in Asset Retirement Obligations | The reconciliation of the changes in our AROs is presented below:
(1) Current portion of asset retirement obligations is recorded in Accrued and other current liabilities.
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Business Segments (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Segment Reporting [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Segment Information | The following table presents information about the Company's single segment for the years ended December 31, .
(1)A component of Cost of goods sold. (2)Includes raw materials, labor, energy, freight costs, FIFO inventory adjustments and other direct cost of goods sold. (3)Advanced production credit related to Section 45X of the IRA. (4)Includes inventory revaluation to lower of cost or net realizable value and changes in inventory reserve. (5)Represents the depreciation expenses and expenses related to leased assets that are directly related to the cost of goods sold.
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| Schedule of Long-Lived Assets |
(1)Includes long-lived assets other than financial instruments and deferred taxes.
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Derivatives (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative Instruments and Hedging Activities Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Derivatives Not Designated as Hedging Instruments | The following table sets forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of December 31, 2025 and 2024, respectively:
(1)Commodity contracts reflect our outstanding LME and MWP forward financial sales contracts, fixed for floating swaps, HFO price swaps and Indiana Hub power price swaps. At December 31, 2025 and December 31, 2024, there were no commodity contracts with Glencore. (2)Foreign exchange contracts reflect our outstanding FX swaps and casthouse currency hedges.
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| Schedule of Derivative Instruments | The following table summarizes the net gain (loss) on forward and derivative contracts for the years ended December 31, 2025, 2024, and 2023:
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Variable Interest Entity (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Consolidated VIE's Assets and Liabilities | The table below shows the carrying amounts and classification of the consolidated VIE's assets and liabilities included in the Consolidated Balance Sheets as of December 31, 2025 and 2024.
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Restatement of Previously Issued Financial Statements (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Error Corrections and Prior Period Adjustments | The effects of the corrections described above on the Company’s Consolidated Statements of Operations were as follows:
The effects of the corrections described above on the Company's Consolidated Statements of Comprehensive Income (Loss) were as follows:
The effects of the corrections described above on the Company's Consolidated Balance Sheets were as follows:
The effects of the corrections described above on the Company’s Consolidated Statements of Cash Flows were as follows:
The effects of the corrections described above on the Company's Consolidated Statements of Shareholder's Equity were as follows:
|
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Quarterly Financial Information (Unaudited and Restated) (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Quarterly Financial Information Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Quarterly Financial Information | The restatement impacts to the Company's consolidated statements of operations were as shown below.
The restatement impacts to the Company's consolidated balance statements were as shown below (dollars in millions).
The restatement impacts to the Company's consolidated statements of shareholders' equity as shown below (dollars in millions).
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Summary of Significant Accounting Policies (Details) |
Dec. 31, 2025 |
Dec. 31, 2023 |
|---|---|---|
| Minimum | Building and Improvements | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 10 years | |
| Minimum | Machinery and Equipment | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 5 years | |
| Minimum | Technology and Software | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 3 years | |
| Maximum | Building and Improvements | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 45 years | |
| Maximum | Machinery and Equipment | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 35 years | |
| Maximum | Technology and Software | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Useful life | 7 years | |
| Jamalco | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Ownership percentage | 55.00% | 55.00% |
| Century Aluminum Company | Glencore | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Glencore beneficial ownership | 36.40% |
Acquisition of Jamalco - Narrative (Details) - USD ($) |
3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
May 02, 2023 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Business Combination [Line Items] | |||||
| Bargain purchase gain | $ 0 | $ 245,900,000 | $ 0 | ||
| General Alumina Holdings Limited | |||||
| Business Combination [Line Items] | |||||
| Payments to acquire business | $ 1.00 | ||||
| Bargain purchase gain | $ 245,900,000 | 273,400,000 | |||
| Property, plant and equipment reduction | $ 29,000,000.0 | ||||
| Purchase, gain reduction | $ 29,000,000.0 | ||||
| Jamalco | |||||
| Business Combination [Line Items] | |||||
| Revenue since acquisition | 150,300,000 | ||||
| Loss of acquiree since acquisition | 45,400,000 | ||||
| Transaction costs | $ 1,400,000 | ||||
| Jamalco | |||||
| Business Combination [Line Items] | |||||
| Ownership percentage | 55.00% | 55.00% | |||
| Jamalco | General Alumina Holdings Limited | |||||
| Business Combination [Line Items] | |||||
| Ownership percentage | 55.00% | ||||
| Jamalco | Clarendon Alumina Production Limited | |||||
| Business Combination [Line Items] | |||||
| Glencore beneficial ownership | 45.00% | ||||
Acquisition of Jamalco - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions |
Dec. 31, 2023 |
May 02, 2023 |
|---|---|---|
| Business Combination [Line Items] | ||
| Bargain purchase gain | $ 273.4 | |
| General Alumina Holdings Limited | ||
| Business Combination [Line Items] | ||
| Cash and cash equivalents | $ 19.4 | |
| Restricted cash | 8.3 | |
| Accounts receivable - net | 7.7 | |
| Non-trade receivables | 40.4 | |
| Inventories | 103.9 | |
| Prepaid and other current assets | 4.2 | |
| Property, plant and equipment | 375.6 | |
| Other assets | 26.3 | |
| Accounts payable, trade | (94.6) | |
| Accrued and other current liabilities | (29.5) | |
| Other liabilities | (36.5) | |
| Asset retirement obligations | (36.0) | |
| Total identifiable assets acquired and liabilities assumed | 389.2 | |
| Less: noncontrolling interest | 143.3 | |
| Bargain purchase gain | $ 245.9 |
Acquisition of Jamalco - Unaudited Pro Forma Financial Information (Details) - General Alumina Holdings Limited - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2023 |
Dec. 31, 2022 |
|
| Business Combination [Line Items] | ||
| Revenue | $ 2,235.1 | $ 2,831.0 |
| Earnings | $ (50.2) | $ (33.1) |
Curtailment of Operations - Hawesville (Details) - Curtailment Of Operations - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Restructuring Cost and Reserve [Line Items] | ||
| Severance costs | $ 6.8 | $ 16.6 |
| Gain on material sales | $ 0.5 | 1.7 |
| Temporary Facility Closing, Excess Capacity | ||
| Restructuring Cost and Reserve [Line Items] | ||
| Excess capacity charges | $ 9.0 | |
| Restructuring Incurred Cost, Statement Of Income Or Comprehensive Income, Extensible Enumeration, Not Disclosed Flag | demand capacity charges | |
Related Party Transactions - Narrative (Details) € in Millions, $ in Millions |
1 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Oct. 01, 2024
USD ($)
|
Dec. 31, 2024
EUR (€)
carbon_credit
€ / carbonCredit
|
Aug. 31, 2024
EUR (€)
carbon_credit
€ / carbonCredit
|
Dec. 31, 2023
EUR (€)
carbon_credit
€ / carbonCredit
|
Sep. 30, 2023
EUR (€)
carbon_credit
€ / carbonCredit
|
Dec. 31, 2025
USD ($)
|
Dec. 31, 2024
USD ($)
carbon_credit
€ / carbonCredit
|
Dec. 31, 2023
USD ($)
carbon_credit
€ / carbonCredit
|
Nov. 30, 2025
shares
|
Aug. 31, 2025
carbon_credit
|
|
| Related Party Transaction [Line Items] | ||||||||||
| Total net sales | $ | $ 2,527.9 | $ 2,220.3 | $ 2,185.4 | |||||||
| Glencore | Supply Commitment | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Total net sales | $ | $ 206.6 | $ 191.3 | $ 191.7 | |||||||
| Glencore | Sales Revenue | Customer Concentration Risk | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Concentration risk, percentage | 54.00% | 59.10% | 73.80% | |||||||
| Vlissingen | Vlissingen Facility Agreement | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Term extension | 2 years | |||||||||
| Credit facility face amount | $ | $ 90.0 | |||||||||
| Stated interest rate, percentage | 8.75% | |||||||||
| Debt instrument, basis spread on variable rate | 3.687% | |||||||||
| Vlissingen | Vlissingen Facility Agreement | Affiliated Entity | Maximum | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Variable interest rate | 9.00% | |||||||||
| Vlissingen | Vlissingen Facility Agreement | Affiliated Entity | Minimum | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Variable interest rate | 7.00% | |||||||||
| Nordural Grundartangi ehf | Carbon Credit Sale | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 370,700 | 390,000 | 370,700 | |||||||
| Sale price (Euro per carbon credit) | € / carbonCredit | 82.18 | |||||||||
| Aggregate amount | € | € 32.1 | |||||||||
| Nordural Grundartangi ehf | Carbon Credit Repurchase | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Sale price (Euro per carbon credit) | € / carbonCredit | 69.16 | 83.72 | 69.16 | |||||||
| Aggregate amount | € | € 25.6 | € 32.7 | ||||||||
| Nordural Grundartangi ehf | Repurchase Agreement, Carbon Credits Settled | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 19,300 | 19,300 | 370,700 | |||||||
| Nordural Grundartangi ehf | Second Repurchase Agreement | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 59,300 | |||||||||
| Sale price (Euro per carbon credit) | € / carbonCredit | 186.74 | |||||||||
| Aggregate amount | € | € 11.1 | |||||||||
| Nordural Grundartangi ehf | Second Repurchase Agreement, Carbon Credit Sale | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 40,000 | 40,000 | ||||||||
| Sale price (Euro per carbon credit) | € / carbonCredit | 69.30 | 69.30 | ||||||||
| Nordural Grundartangi ehf | Second Repurchase Agreement, Carbon Credit Repurchase | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Sale price (Euro per carbon credit) | € / carbonCredit | 70.71 | 70.71 | ||||||||
| Aggregate amount | € | € 2.8 | |||||||||
| Nordural Grundartangi ehf | Second Repurchase Agreement, Carbon Credit Increase | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 19,300 | |||||||||
| Nordural Grundartangi ehf | Second Repurchase Agreement, Carbon Credit Settled | Affiliated Entity | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Carbon credit sold in transaction | 59,300 | |||||||||
| Century Aluminum Company | Glencore | ||||||||||
| Related Party Transaction [Line Items] | ||||||||||
| Glencore beneficial ownership | 36.40% | |||||||||
| Stock sold during period (in shares) | shares | 9,000,000 | |||||||||
Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Related Party Transaction [Line Items] | |||
| Net sales | $ 2,527.9 | $ 2,220.3 | $ 2,185.4 |
| Related Party | |||
| Related Party Transaction [Line Items] | |||
| Net sales | 1,365.5 | 1,312.1 | 1,612.1 |
| Related Party | Glencore | |||
| Related Party Transaction [Line Items] | |||
| Net sales | 1,365.5 | 1,312.1 | 1,612.1 |
| Purchases from Glencore | $ 294.0 | $ 277.9 | $ 181.4 |
Revenue - Breakdown of Revenue (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Disaggregation of Revenue [Line Items] | |||
| Contract liabilities | $ 31.2 | $ 41.2 | |
| Net sales | 2,527.9 | 2,220.3 | $ 2,185.4 |
| Aluminum | |||
| Disaggregation of Revenue [Line Items] | |||
| Net sales | 2,244.2 | 1,882.1 | 1,972.6 |
| Alumina | |||
| Disaggregation of Revenue [Line Items] | |||
| Net sales | 283.7 | 338.2 | 212.8 |
| United States | |||
| Disaggregation of Revenue [Line Items] | |||
| Net sales | 1,734.7 | 1,427.0 | 1,358.6 |
| Iceland | |||
| Disaggregation of Revenue [Line Items] | |||
| Net sales | $ 793.2 | $ 793.3 | $ 826.8 |
Leases - Narratives (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Leases [Abstract] | |||
| Operating lease, weighted average remaining lease term | 9 years 2 months 12 days | 10 years 1 month 6 days | |
| Operating lease, weighted average discount rate, percent | 7.40% | 7.50% | |
| Right-of-use asset obtained in exchange for operating lease liability | $ 3.7 | $ 2.0 | |
| Operating lease, payments | $ 5.3 | $ 5.0 | $ 4.6 |
Leases - ROU (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Leases [Abstract] | ||
| ROUA [extensible list] | Other assets | Other assets |
| ROUA | $ 24.4 | $ 21.0 |
| Lease Liability - current [extensible list] | Accrued and other current liabilities | Accrued and other current liabilities |
| Lease Liability - current | $ 2.6 | $ 3.0 |
| Lease Liability - non-current [extensible list] | Other Liabilities, Noncurrent | Other Liabilities, Noncurrent |
| Lease Liability - non-current | $ 22.0 | $ 18.7 |
| Lease liability | $ 24.6 | $ 21.7 |
Leases - Maturities (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Leases [Abstract] | ||
| 2026 | $ 4.3 | |
| 2027 | 3.7 | |
| 2028 | 3.6 | |
| 2029 | 3.5 | |
| 2030 | 3.3 | |
| Thereafter | 16.8 | |
| Total | 35.2 | |
| Less: Interest | (10.6) | |
| Lease liability | $ 24.6 | $ 21.7 |
Leases - Operating Expense (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Leases [Abstract] | |||
| Operating leases expense | $ 5.6 | $ 5.3 | $ 4.9 |
| Short term lease expense | 3.3 | 3.2 | 0.6 |
| Total | $ 8.9 | $ 8.5 | $ 5.5 |
Fair Value Measurements - Recurring Fair Value Measurements (Details) - USD ($) |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| ASSETS: | ||
| Cash equivalents | $ 122,300,000 | $ 7,900,000 |
| Trust assets | 100,000 | 300,000 |
| Derivative instruments | 1,900,000 | 4,500,000 |
| TOTAL | 124,300,000 | 12,700,000 |
| LIABILITIES: | ||
| Derivative instruments | 66,000,000.0 | 4,400,000 |
| TOTAL | 66,000,000.0 | 4,400,000 |
| Level 1 | ||
| ASSETS: | ||
| Cash equivalents | 122,300,000 | 7,900,000 |
| Trust assets | 100,000 | 300,000 |
| Derivative instruments | 0 | 0 |
| TOTAL | 122,400,000 | 8,200,000 |
| LIABILITIES: | ||
| Derivative instruments | 0 | 0 |
| TOTAL | 0 | 0 |
| Level 2 | ||
| ASSETS: | ||
| Cash equivalents | 0 | 0 |
| Trust assets | 0 | 0 |
| Derivative instruments | 1,900,000 | 4,500,000 |
| TOTAL | 1,900,000 | 4,500,000 |
| LIABILITIES: | ||
| Derivative instruments | 66,000,000.0 | 4,400,000 |
| TOTAL | 66,000,000.0 | 4,400,000 |
| Level 3 | ||
| ASSETS: | ||
| Cash equivalents | 0 | 0 |
| Trust assets | 0 | 0 |
| Derivative instruments | 0 | 0 |
| TOTAL | 0 | 0 |
| LIABILITIES: | ||
| Derivative instruments | 0 | 0 |
| TOTAL | $ 0 | $ 0 |
Fair Value Measurements - Narrative (Details) - USD ($) |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Fair Value Measurement Inputs and Valuation Techniques [Line Items] | ||
| Assets, fair value | $ 124,300,000 | $ 12,700,000 |
| Liabilities, fair value | 66,000,000.0 | 4,400,000 |
| Level 3 | ||
| Fair Value Measurement Inputs and Valuation Techniques [Line Items] | ||
| Assets, fair value | 0 | 0 |
| Liabilities, fair value | $ 0 | $ 0 |
Debt - Activity (Details) - USD ($) |
Dec. 31, 2025 |
Jul. 22, 2025 |
Dec. 31, 2024 |
Oct. 01, 2024 |
Apr. 09, 2021 |
|---|---|---|---|---|---|
| Debt Instrument [Line Items] | |||||
| Total | $ 548,300,000 | $ 528,200,000 | |||
| Industrial Revenue Bonds, Variable | |||||
| Debt Instrument [Line Items] | |||||
| Maximum variable interest rate | 12.00% | ||||
| Hancock County industrial revenue bonds ("IRBs") due April 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) | $ 7,800,000 | 7,800,000 | |||
| Revolving Credit Facility | U.S revolving credit facility | |||||
| Debt Instrument [Line Items] | |||||
| Revolving credit facility | $ 0 | 20,000,000.0 | |||
| Stated interest rate, percentage | 7.25% | ||||
| Revolving Credit Facility | Foreign line of credit | |||||
| Debt Instrument [Line Items] | |||||
| Revolving credit facility | $ 61,000,000.0 | 34,000,000.0 | |||
| Stated interest rate, percentage | 7.23% | ||||
| Casthouse Facility | Foreign line of credit | |||||
| Debt Instrument [Line Items] | |||||
| Revolving credit facility | $ 0 | 9,000,000.0 | |||
| Secured debt | 0 | 114,200,000 | |||
| Vlissingen Facility Agreement | Foreign line of credit | |||||
| Debt Instrument [Line Items] | |||||
| Secured debt | $ 0 | 10,000,000.0 | |||
| Stated interest rate, percentage | 7.56% | 8.75% | |||
| Senior Secured Notes, 7.5% | Senior Notes | |||||
| Debt Instrument [Line Items] | |||||
| Stated interest rate, percentage | 7.50% | 7.50% | |||
| 7.5% senior secured notes due April 1, 2028 | $ 0 | 248,100,000 | |||
| Senior Convertible Notes, 2.75% | Senior Notes | |||||
| Debt Instrument [Line Items] | |||||
| Stated interest rate, percentage | 2.75% | 2.75% | |||
| Financing fees | $ 800,000 | ||||
| 2.75% convertible senior notes due May 1, 2028, net of financing fees of $0.8 million at December 31, 2025, interest payable semiannually | $ 85,500,000 | 85,100,000 | |||
| Senior Secured Notes, 6.875% | Senior Notes | |||||
| Debt Instrument [Line Items] | |||||
| Stated interest rate, percentage | 6.875% | 6.875% | |||
| Financing fees | $ 5,900,000 | ||||
| 7.5% senior secured notes due April 1, 2028 | $ 394,000,000.0 | $ 0 | |||
| Industrial revenue bonds due 2028 | |||||
| Debt Instrument [Line Items] | |||||
| Stated interest rate, percentage | 3.45% |
Debt - Narrative (Details) |
1 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Aug. 05, 2025
USD ($)
|
Jul. 22, 2025
USD ($)
|
Oct. 01, 2024
USD ($)
|
Apr. 09, 2021
USD ($)
$ / shares
|
Oct. 31, 2025
USD ($)
|
Dec. 31, 2025
USD ($)
|
Dec. 31, 2024
USD ($)
|
Dec. 31, 2023
USD ($)
|
Jun. 14, 2022
USD ($)
|
Nov. 30, 2013
USD ($)
|
|
| Debt Instrument [Line Items] | ||||||||||
| Proceeds from issuance of Senior Notes due 2032 | $ 400,000,000.0 | $ 0 | $ 0 | |||||||
| Repayments of debt | 250,000,000.0 | 0 | 0 | |||||||
| Loss on early extinguishment of debt | $ 7,700,000 | 0 | 0 | |||||||
| Senior Secured Notes, 6.875% | Senior Notes | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 6.875% | 6.875% | ||||||||
| Face amount | $ 400,000,000.0 | |||||||||
| Proceeds from issuance of Senior Notes due 2032 | $ 393,700,000 | |||||||||
| Redemption price, percentage | 100.00% | |||||||||
| Redemption period | 12 months | |||||||||
| Percentage of outstanding amount, offer to purchase | 101.00% | |||||||||
| Senior Secured Notes, 6.875% | Senior Notes | Level 2 | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Fair value of debt instrument | $ 412,500,000 | |||||||||
| Senior Secured Notes, 7.5% | Senior Notes | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 7.50% | 7.50% | ||||||||
| Repayments of debt | $ 261,100,000 | |||||||||
| Percentage of principal amount redeemed | 101.875% | |||||||||
| Loss on early extinguishment of debt | $ 6,200,000 | |||||||||
| Early redemption and tender premiums | 4,700,000 | |||||||||
| Write-off of deferred financing cost | $ 1,500,000 | |||||||||
| Senior Convertible Notes, 2.75% | Senior Notes | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 2.75% | 2.75% | ||||||||
| Face amount | $ 86,300,000 | |||||||||
| Percentage of principal amount redeemed | 100.00% | 100.00% | ||||||||
| Proceeds from convertible debt | $ 83,700,000 | |||||||||
| Conversion ratio | 0.0533547 | |||||||||
| Conversion price (in dollars per share) | $ / shares | $ 18.74 | |||||||||
| Debt instrument, convertible, threshold percentage of stock price trigger | 130.00% | |||||||||
| Debt instrument, trading days, term | 20 days | |||||||||
| Debt instrument, consecutive trading days, term | 30 days | |||||||||
| Senior Convertible Notes, 2.75% | Senior Notes | Level 2 | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Fair value of debt instrument | $ 181,900,000 | |||||||||
| Revolving Credit Facility | U.S revolving credit facility | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 7.25% | |||||||||
| Credit facility face amount | $ 250,000,000.0 | $ 250,000,000.0 | ||||||||
| Borrowing availability, net of outstanding letters of credit and borrowings | 154,800,000 | |||||||||
| Credit spread adjustment | 0.10% | |||||||||
| Outstanding borrowings | 0 | |||||||||
| Outstanding letters of credit issued | $ 50,500,000 | |||||||||
| Revolving Credit Facility | Letter of Credit | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Borrowing availability, net of outstanding letters of credit and borrowings | $ 150,000,000.0 | |||||||||
| Revolving Credit Facility | Foreign line of credit | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 7.23% | |||||||||
| Credit facility face amount | $ 100,000,000.0 | $ 100,000,000.0 | ||||||||
| Outstanding borrowings | 61,000,000.0 | |||||||||
| Outstanding letters of credit issued | 0 | |||||||||
| Casthouse Facility | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Repayments under Grundartangi casthouse debt facility | 123,200,000 | 6,800,000 | $ 0 | |||||||
| Casthouse Facility | Foreign line of credit | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Loss on early extinguishment of debt | $ 1,500,000 | |||||||||
| Repayments under Grundartangi casthouse debt facility | 116,400,000 | |||||||||
| Repayments of accrued interest on debt | $ 1,900,000 | |||||||||
| Secured debt | $ 0 | 114,200,000 | ||||||||
| Vlissingen Facility Agreement | Foreign line of credit | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Stated interest rate, percentage | 8.75% | 7.56% | ||||||||
| Credit facility face amount | $ 90,000,000 | |||||||||
| Term extension | 2 years | |||||||||
| Secured debt | $ 0 | $ 10,000,000.0 | ||||||||
| Debt instrument, basis spread on variable rate | 3.687% | |||||||||
| Vlissingen Facility Agreement | Foreign line of credit | Maximum | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Variable interest rate | 9.00% | |||||||||
| Vlissingen Facility Agreement | Foreign line of credit | Minimum | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Variable interest rate | 7.00% | |||||||||
| Industrial Revenue Bonds, Variable | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Maximum variable interest rate | 12.00% | |||||||||
| Surety Bond | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Loss contingency accrual | $ 6,600,000 | |||||||||
Debt - Redemption Rights (Details) - Senior Secured Notes, 6.875% - Long-term Debt |
12 Months Ended |
|---|---|
Dec. 31, 2025 | |
| 2028 | |
| Debt Instrument [Line Items] | |
| Redemption price, percentage | 103.438% |
| 2029 | |
| Debt Instrument [Line Items] | |
| Redemption price, percentage | 101.719% |
| 2030 and Thereafter | |
| Debt Instrument [Line Items] | |
| Redemption price, percentage | 100.00% |
Debt - U.S. Credit Facility Schedule (Details) - U.S revolving credit facility - Revolving Credit Facility - USD ($) |
Jul. 22, 2025 |
Dec. 31, 2025 |
Jun. 14, 2022 |
|---|---|---|---|
| Line of Credit Facility [Line Items] | |||
| Credit facility maximum amount | $ 250,000,000.0 | $ 250,000,000.0 | |
| Borrowing availability | 205,300,000 | ||
| Outstanding letters of credit issued | 50,500,000 | ||
| Outstanding borrowings | 0 | ||
| Borrowing availability, net of outstanding letters of credit and borrowings | $ 154,800,000 | ||
| Credit spread adjustment | 0.10% |
Debt - Iceland Credit Facility Schedule (Details) - Foreign line of credit - Revolving Credit Facility - USD ($) $ in Millions |
Dec. 31, 2025 |
Nov. 30, 2013 |
|---|---|---|
| Line of Credit Facility [Line Items] | ||
| Credit facility maximum amount | $ 100.0 | $ 100.0 |
| Borrowing availability | 100.0 | |
| Outstanding letters of credit issued | 0.0 | |
| Outstanding borrowings | 61.0 | |
| Borrowing availability, net of outstanding letters of credit and borrowings | $ 39.0 |
Shareholders' Equity (Details) - USD ($) |
129 Months Ended | ||||||
|---|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Nov. 30, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Mar. 31, 2015 |
Dec. 31, 2011 |
Dec. 31, 2008 |
|
| Class of Stock [Line Items] | |||||||
| Common stock, shares authorized (in shares) | 195,000,000 | 195,000,000 | |||||
| Common stock, par value (in dollars per share) | $ 0.01 | $ 0.01 | |||||
| Common stock, shares issued (in shares) | 106,155,528 | 100,475,086 | |||||
| Common stock, shares outstanding (in shares) | 98,969,007 | 93,288,565 | |||||
| Preferred stock, shares authorized (in shares) | 5,000,000 | 5,000,000 | |||||
| Preferred stock, par value (in dollars per share) | $ 0.01 | $ 0.01 | |||||
| Conversion of convertible preferred stock (in shares) | 100 | ||||||
| Authorized repurchase amount | $ 130,000,000.0 | $ 60,000,000.0 | |||||
| Additional repurchase amount | $ 70,000,000.0 | ||||||
| Treasury stock, common (in shares) | 7,186,521 | ||||||
| Treasury stock, value | $ 86,300,000 | $ 86,300,000 | $ 86,300,000 | ||||
| Repurchase of common stock (in shares) | 0 | ||||||
| Remaining authorized repurchase amount | $ 43,700,000 | ||||||
| Glencore | Century Aluminum Company | |||||||
| Class of Stock [Line Items] | |||||||
| Stock sold during period (in shares) | 9,000,000 | ||||||
| Series A Convertible Preferred Stock | |||||||
| Class of Stock [Line Items] | |||||||
| Preferred stock, par value (in dollars per share) | $ 0.01 | ||||||
| Preferred stock, shares issued (in shares) | 160,000 | ||||||
| Shares, outstanding (in shares) | 0 | 49,715 |
Inventories - Schedule of Inventories (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| Inventory, Net [Abstract] | |||
| Raw materials | $ 161.5 | $ 180.8 | |
| Work-in-process | 52.2 | 52.1 | |
| Finished goods | 36.5 | 74.6 | |
| Operating and other supplies | 269.4 | 231.5 | |
| Inventories | $ 519.6 | $ 539.0 | $ 477.0 |
Inventories - Narrative (Details) $ in Millions |
12 Months Ended |
|---|---|
|
Dec. 31, 2025
USD ($)
| |
| Inventory, Net [Abstract] | |
| Inventory markdown | $ 8.4 |
Property, Plant and Equipment (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|---|---|---|---|---|---|
| Property, Plant and Equipment [Abstract] | |||||||||
| Land and improvements | $ 174.0 | $ 167.1 | |||||||
| Mineral Reserves | 63.0 | 63.0 | |||||||
| Buildings and improvements | 782.6 | 421.4 | |||||||
| Machinery and equipment | 1,360.1 | 1,711.5 | |||||||
| Asset Retirement Obligation | 86.0 | 63.7 | |||||||
| Construction in progress | 114.2 | 44.7 | |||||||
| Property, plant and equipment, gross | 2,579.9 | 2,471.4 | |||||||
| Less accumulated depreciation, amortization and depletion | (1,412.3) | (1,321.6) | |||||||
| Property, plant and equipment - net | $ 1,167.6 | $ 1,139.2 | $ 1,150.8 | $ 1,142.0 | $ 1,149.8 | $ 1,129.7 | $ 1,129.5 | $ 1,137.9 | $ 1,184.2 |
Property, Plant and Equipment (Detail Textual) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Property, Plant and Equipment [Abstract] | |||
| Depreciation, depletion and amortization | $ 91.8 | $ 86.7 | $ 79.0 |
Accumulated Other Comprehensive Loss ("AOCL") - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other comprehensive loss before income tax effect | $ (57.5) | $ (105.6) | |
| Income tax effect | 2.3 | 2.3 | |
| Accumulated other comprehensive loss | (55.2) | (103.3) | $ (97.9) |
| Defined benefit plan and other postretirement liabilities | |||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other comprehensive loss before income tax effect | (58.7) | (107.0) | |
| Income tax effect | 2.6 | 2.6 | |
| Unrealized gain (loss) on financial instruments | |||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | |||
| Other comprehensive loss before income tax effect | 1.2 | 1.4 | |
| Income tax effect | $ (0.3) | $ (0.3) |
Accumulated Other Comprehensive Loss ("AOCL") - Components of AOCL (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||
| Beginning balance | $ 805.4 | $ 503.2 | $ 399.3 |
| Other comprehensive income (loss) before reclassifications | 42.0 | (11.9) | (10.1) |
| Net amount reclassified to net income (loss) | 6.1 | 6.5 | 6.2 |
| Ending balance | 929.9 | 805.4 | 503.2 |
| Defined benefit plan and other postretirement liabilities | |||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||
| Beginning balance | (104.6) | (99.4) | (95.6) |
| Other comprehensive income (loss) before reclassifications | 42.0 | (11.9) | (10.1) |
| Net amount reclassified to net income (loss) | 6.2 | 6.7 | 6.3 |
| Ending balance | (56.4) | (104.6) | (99.4) |
| Unrealized gain (loss) on financial instruments | |||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||
| Beginning balance | 1.3 | 1.5 | 1.6 |
| Other comprehensive income (loss) before reclassifications | 0.0 | 0.0 | 0.0 |
| Net amount reclassified to net income (loss) | (0.1) | (0.2) | (0.1) |
| Ending balance | 1.2 | 1.3 | 1.5 |
| Accumulated other comprehensive loss | |||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||
| Beginning balance | (103.3) | (97.9) | (94.0) |
| Ending balance | $ (55.2) | $ (103.3) | $ (97.9) |
Accumulated Other Comprehensive Loss ("AOCL") - Reclassifications out of AOCL (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
||||||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | ||||||||||||||
| Cost of goods sold | $ (557.3) | $ (594.5) | $ (576.6) | $ (462.2) | $ (545.3) | $ (476.5) | $ (2,271.5) | [1] | $ (2,048.3) | [1] | $ (2,097.8) | [1] | ||
| Other income, net | (14.5) | (5.5) | (3.3) | |||||||||||
| Selling, general and administrative expenses | (79.9) | (56.8) | (44.3) | |||||||||||
| Other operating expenses - net | (18.4) | (6.8) | (15.8) | |||||||||||
| Income tax benefit (expense) | 13.1 | (3.2) | 14.6 | |||||||||||
| Net of tax | $ 8.2 | $ (11.7) | $ 22.4 | $ 37.4 | $ (11.6) | $ 241.2 | 15.8 | 306.7 | (56.6) | |||||
| Reclassification out of Accumulated Other Comprehensive Income | Defined benefit plan and other postretirement liabilities | ||||||||||||||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | ||||||||||||||
| Cost of goods sold | 8.4 | (8.5) | (1.0) | |||||||||||
| Other income, net | 0.0 | 0.0 | 0.0 | |||||||||||
| Selling, general and administrative expenses | 0.1 | 1.1 | (0.2) | |||||||||||
| Other operating expenses - net | 39.7 | 2.2 | (2.6) | |||||||||||
| Income tax benefit (expense) | 0.0 | 0.0 | 0.0 | |||||||||||
| Net of tax | 48.2 | (5.2) | (3.8) | |||||||||||
| Reclassification out of Accumulated Other Comprehensive Income | Unrealized gain (loss) on financial instruments | ||||||||||||||
| Accumulated Other Comprehensive Income (Loss) [Line Items] | ||||||||||||||
| Cost of goods sold | (0.1) | (0.2) | (0.1) | |||||||||||
| Income tax benefit (expense) | 0.0 | 0.0 | 0.0 | |||||||||||
| Net of tax | $ (0.1) | $ (0.2) | $ (0.1) | |||||||||||
| ||||||||||||||
Pension and Other Postretirement Benefits - Change in benefit obligation (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Pension | |||
| Change in benefit obligation [Roll Forward] | |||
| Benefit obligation at beginning of year | $ 342.5 | $ 332.3 | |
| Service cost | 2.6 | 5.1 | $ 3.3 |
| Interest cost | 14.0 | 20.1 | 17.3 |
| Actuarial (gain) loss | 7.7 | 6.5 | |
| Medicare Part D | 0.0 | 0.0 | |
| Benefits paid | (19.4) | (22.6) | |
| Exchange rates | 0.0 | (0.7) | |
| Plan participants' contributions | 0.0 | 1.8 | |
| Benefit obligation at end of year | 347.4 | 342.5 | 332.3 |
| OPEB | |||
| Change in benefit obligation [Roll Forward] | |||
| Benefit obligation at beginning of year | 77.0 | 77.7 | |
| Service cost | 0.1 | 0.2 | 0.1 |
| Interest cost | 4.2 | 4.0 | 3.9 |
| Actuarial (gain) loss | (37.5) | 0.6 | |
| Medicare Part D | 0.2 | 0.2 | |
| Benefits paid | (5.1) | (5.7) | |
| Exchange rates | 0.0 | 0.0 | |
| Plan participants' contributions | 0.0 | 0.0 | |
| Benefit obligation at end of year | $ 38.9 | $ 77.0 | $ 77.7 |
Pension and Other Postretirement Benefits - Change in Plan Assets (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Pension | ||
| Change in fair value of plan assets [Roll Forward] | ||
| Fair value of plan assets at beginning of year | $ 272.2 | $ 282.9 |
| Actual return on plan assets | 27.0 | 8.3 |
| Acquisition | 0.0 | 0.0 |
| Employer contributions | 8.9 | 2.5 |
| Medicare Part D subsidy received | 0.0 | 0.0 |
| Benefits paid | (19.4) | (22.7) |
| Exchange rates | 0.0 | (0.6) |
| Plan participants' contributions | 0.0 | 1.8 |
| Fair value of assets at end of year | 288.7 | 272.2 |
| OPEB | ||
| Change in fair value of plan assets [Roll Forward] | ||
| Fair value of plan assets at beginning of year | 0.0 | 0.0 |
| Actual return on plan assets | 0.0 | 0.0 |
| Acquisition | 0.0 | 0.0 |
| Employer contributions | 4.9 | 5.5 |
| Medicare Part D subsidy received | 0.2 | 0.2 |
| Benefits paid | (5.1) | (5.7) |
| Exchange rates | 0.0 | 0.0 |
| Plan participants' contributions | 0.0 | |
| Fair value of assets at end of year | $ 0.0 | $ 0.0 |
Pension and Other Postretirement Benefits - Funded status of plans (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Pension | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Funded status | $ (58.7) | $ (70.3) |
| Current liabilities | (1.7) | (15.0) |
| Non-current liabilities | (57.0) | (55.3) |
| Net amount recognized | (58.7) | (70.3) |
| Net loss (gain) | 78.5 | 88.1 |
| Prior service cost (benefit) | 1.4 | 1.6 |
| Total | 79.9 | 89.7 |
| Projected benefit obligation for plans with accumulated benefit obligations in excess of plan assets | 347.4 | 342.5 |
| Accumulated benefit obligation for plans with accumulated benefit obligations in excess of plan assets | 318.0 | 303.4 |
| Fair value of plan assets for plans with accumulated benefit obligations in excess of plan assets | 288.7 | 272.2 |
| OPEB | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Funded status | (38.9) | (77.0) |
| Current liabilities | (3.5) | (6.6) |
| Non-current liabilities | (35.4) | (70.4) |
| Net amount recognized | (38.9) | (77.0) |
| Net loss (gain) | (23.9) | 14.7 |
| Prior service cost (benefit) | 0.0 | 0.0 |
| Total | $ (23.9) | $ 14.7 |
Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Pension | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Service cost | $ 2.6 | $ 5.1 | $ 3.3 |
| Interest cost | 14.0 | 20.1 | 17.3 |
| Expected return on plan assets | (14.9) | (20.4) | (17.3) |
| Amortization of prior service costs | 0.2 | 0.2 | 0.1 |
| Amortization of net loss | 5.1 | 5.8 | 6.0 |
| Total net periodic benefit cost | 7.0 | 10.8 | 9.4 |
| OPEB | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Service cost | 0.1 | 0.2 | 0.1 |
| Interest cost | 4.2 | 4.0 | 3.9 |
| Expected return on plan assets | 0.0 | 0.0 | 0.0 |
| Amortization of prior service costs | 0.0 | 0.0 | 0.0 |
| Amortization of net loss | 0.9 | 0.7 | 0.1 |
| Total net periodic benefit cost | $ 5.2 | $ 4.9 | $ 4.1 |
Pension and Other Postretirement Benefits - Changes in Plan Assets & Benefit Obligation Recognized in OCI (pre-taxed) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Defined Benefit Plan Disclosure [Line Items] | |||
| Net (gain) loss | $ (42.0) | $ 13.1 | $ 19.2 |
| Amortization of prior service (cost) benefit, including curtailment | (0.2) | (0.2) | (0.1) |
| Net periodic benefit cost | 12.1 | 15.7 | $ 13.5 |
| Pension | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Net (gain) loss | (4.4) | 18.4 | |
| Amortization of net loss, including recognition due to settlement | (5.1) | (5.8) | |
| Amortization of prior service (cost) benefit, including curtailment | (0.2) | (0.2) | |
| Exchange rates | 0.0 | (4.4) | |
| Total amount recognized in other comprehensive income (loss) | (9.7) | 8.0 | |
| Net periodic benefit cost | 7.0 | 10.8 | |
| Total recognized in net periodic benefit cost and other comprehensive income (loss) | (2.7) | 18.8 | |
| OPEB | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Net (gain) loss | (37.5) | 0.6 | |
| Amortization of net loss, including recognition due to settlement | (0.9) | (0.7) | |
| Amortization of prior service (cost) benefit, including curtailment | 0.0 | 0.0 | |
| Exchange rates | 0.0 | 0.0 | |
| Total amount recognized in other comprehensive income (loss) | (38.4) | (0.1) | |
| Net periodic benefit cost | 5.2 | 4.9 | |
| Total recognized in net periodic benefit cost and other comprehensive income (loss) | $ (33.2) | $ 4.8 | |
Pension and Other Postretirement Benefits - Weighted Average assumptions used in calculating benefit obligations (Details) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Pension | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Discount rate | 6.00% | 5.99% |
| Measurement date | Dec. 31, 2025 | Dec. 31, 2024 |
| Pension | United States | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Rate of compensation increase | 3.20% | 3.00% |
| Pension | Jamaica | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Rate of compensation increase | 7.00% | 7.00% |
| OPEB | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Discount rate | 5.39% | 5.62% |
| Measurement date | Dec. 31, 2025 | Dec. 31, 2024 |
| OPEB | United States | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Rate of compensation increase | 3.20% | 3.00% |
| OPEB | Jamaica | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Rate of compensation increase | 7.00% | 7.00% |
Pension and Other Postretirement Benefits - Weighted average assumptions used to determine net periodic benefit cost (Details) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Pension | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Measurement date | 12/31/2024 | 12/31/2023 | 12/31/2022 |
| Fiscal year end | 12/31/2025 | 12/31/2024 | 12/31/2023 |
| Discount rate | 5.68% | 6.75% | 5.50% |
| Expected return on plan assets | 7.40% | 7.28% | 7.25% |
| Pension | United States | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Rate of compensation increase, group 1 | 3.20% | 3.50% | 4.00% |
| Rate of compensation increase, group 2 | 3.50% | ||
| Pension | Jamaica | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Rate of compensation increase, group 1 | 7.00% | 9.00% | |
| OPEB | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Measurement date | 12/31/2024 | 12/31/2023 | 12/31/2022 |
| Fiscal year end | 12/31/2025 | 12/31/2024 | 12/31/2023 |
| Discount rate | 5.59% | 5.43% | 5.57% |
| Expected return on plan assets | 0.00% | 0.00% | 0.00% |
| OPEB | United States | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Rate of compensation increase, group 1 | 3.20% | 3.50% | 4.00% |
| Rate of compensation increase, group 2 | 3.50% | ||
| OPEB | Jamaica | |||
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |||
| Rate of compensation increase, group 1 | 7.00% | 8.00% | |
Pension and Other Postretirement Benefits - Assumed health care trend rates (Details) |
Dec. 31, 2025 |
|---|---|
| Pre 65 | United States | |
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |
| Medical cost inflation rate | 8.50% |
| Medical cost inflation, years 13 and thereafter | 4.50% |
| Pre 65 | Jamaica | |
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |
| Medical cost inflation rate | 8.00% |
| Post 65 | United States | |
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |
| Medical cost inflation rate | 8.50% |
| Medical cost inflation, years 13 and thereafter | 4.50% |
| Post 65 | Jamaica | |
| Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] | |
| Medical cost inflation rate | 8.00% |
Pension and Other Postretirement Benefits - Pension Plan Asset Allocation (Details) |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 100.00% | |
| Actual plan asset allocations | 100.00% | 100.00% |
| Global equity | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 45.00% | |
| Actual plan asset allocations | 46.00% | 51.00% |
| Diversified credit | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 15.00% | |
| Actual plan asset allocations | 17.00% | 17.00% |
| Real assets | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 10.00% | |
| Actual plan asset allocations | 11.00% | 11.00% |
| Liability hedging assets | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 30.00% | |
| Actual plan asset allocations | 25.00% | 20.00% |
| Cash | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Target allocation percentage of assets | 0.00% | |
| Actual plan asset allocations | 1.00% | 1.00% |
Pension and Other Postretirement Benefits - Fair Value Hierarchy (Details) - Pension - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | $ 288.7 | $ 272.2 | $ 282.9 |
| Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 59.2 | 59.2 | |
| Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 1.1 | 1.1 | |
| Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 228.4 | 211.9 | |
| Cash | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 4.5 | 4.1 | |
| Cash | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 1.3 | 1.3 | |
| Cash | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Cash | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Cash | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 3.2 | 2.8 | |
| Global equity | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 141.1 | 144.4 | |
| Global equity | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 36.3 | 36.3 | |
| Global equity | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Global equity | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Global equity | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 104.8 | 108.1 | |
| Diversified credit | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 59.9 | 56.7 | |
| Diversified credit | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 21.4 | 21.4 | |
| Diversified credit | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Diversified credit | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Diversified credit | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 38.5 | 35.3 | |
| Real assets | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 25.0 | 23.1 | |
| Real assets | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Real assets | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | ||
| Real assets | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Real assets | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 25.0 | 23.1 | |
| Liability hedging assets | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 56.9 | 42.6 | |
| Liability hedging assets | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Liability hedging assets | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Liability hedging assets | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Liability hedging assets | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 56.9 | 42.6 | |
| Other | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 1.3 | 1.3 | |
| Other | Level 1 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.2 | 0.2 | |
| Other | Level 2 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 1.1 | 1.1 | |
| Other | Level 3 | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | 0.0 | 0.0 | |
| Other | Assets measured at NAV | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Fair value of assets | $ 0.0 | $ 0.0 |
Pension and Other Postretirement Benefits - Expected Contribution Cash Flows (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Pension | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Employer contributions | $ 8.9 | $ 2.5 |
| Expected contributions in next twelve months | 14.8 | |
| Defined Benefit Plan, Expected Future Benefit Payment [Abstract] | ||
| 2026 | 22.1 | |
| 2027 | 22.3 | |
| 2028 | 23.0 | |
| 2029 | 23.6 | |
| 2030 | 24.4 | |
| 2031 – 2035 | 134.1 | |
| Pension | United States and Jamaica Pension Plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Employer contributions | 9.2 | 2.5 |
| OPEB | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Employer contributions | 4.9 | 5.5 |
| Expected contributions in next twelve months | 3.6 | |
| Defined Benefit Plan, Expected Future Benefit Payment [Abstract] | ||
| 2026 | 3.6 | |
| 2027 | 3.5 | |
| 2028 | 3.6 | |
| 2029 | 3.6 | |
| 2030 | 3.3 | |
| 2031 – 2035 | 14.6 | |
| OPEB | United States and Jamaica Pension Plans | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Employer contributions | $ 5.0 | $ 5.5 |
Pension and Other Postretirement Benefits - Participation in Multi-Employer Pension Plans (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Retirement Benefits [Abstract] | |||
| EIN | 236648508 | ||
| PN | 499 | ||
| Pension protection act zone status | Green | Green | |
| Subject to financial improvement/rehabilitation plan | No | ||
| Contributions of century aluminum company | $ 30 | $ 40 | $ 200 |
| Withdrawal from Plan Probable | No | ||
| Surcharge Imposed | No | ||
| Expiration date of collective bargaining agreement | Mar. 31, 2026 | ||
Pension and Other Postretirement Benefits - Company matching contribution to defined contribution 401(K) plans (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Retirement Benefits [Abstract] | |||
| Age requirement for future accruals | 50 years | ||
| Company matching contribution to defined contribution (401(k)) plans | $ 6.7 | $ 6.3 | $ 5.8 |
Share-based Compensation - Narratives (Details) |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2025
USD ($)
award_type
shares
|
Dec. 31, 2024
USD ($)
|
Dec. 31, 2023
USD ($)
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share-based payment arrangement, amount capitalized | $ 0 | $ 0 | $ 0 |
| Unrecognized compensation expense | $ 23,500,000 | ||
| Weighted average period of expense recognition | 1 year 2 months 12 days | ||
| Amended and Restated Stock Option Plan | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share based compensation, vesting rights (in time period) | 3 years | ||
| Shares authorized (in shares) | shares | 12,900,000 | ||
| Shares remaining (in shares) | shares | 1,899,785 | ||
| Amended and Restated Stock Option Plan | Non-employee director | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share based compensation, vesting rights (in time period) | 12 months | ||
| Long Term Incentive Plan | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Share based compensation, vesting rights (in time period) | 3 years | ||
| Number of award types provided | award_type | 2 | ||
| Performance unit liability | $ 11,800,000 | $ 7,100,000 | |
Share-based Compensation - Service Based Awards Rollforward (Details) - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Weighted-Average Grant Date Fair Value | |||
| Granted (in dollars per share) | $ 13.05 | $ 10.11 | $ 12.58 |
| Service-Based Share Awards | |||
| Number | |||
| Beginning balance (in shares) | 1,404,895 | ||
| Granted (in shares) | 415,565 | ||
| Vested (in shares) | (535,301) | ||
| Forfeited (in shares) | (140,385) | ||
| Ending balance (in shares) | 1,144,774 | 1,404,895 | |
| Weighted-Average Grant Date Fair Value | |||
| Beginning balance (in dollars per share) | $ 9.79 | ||
| Granted (in dollars per share) | 19.47 | ||
| Vested (in dollars per share) | 9.45 | ||
| Forfeited (in dollars per share) | 11.63 | ||
| Ending balance (in dollars per share) | $ 13.24 | $ 9.79 | |
| Performance-based share awards | |||
| Number | |||
| Beginning balance (in shares) | 774,475 | ||
| Granted (in shares) | 590,391 | ||
| Vested (in shares) | (711,414) | ||
| Forfeited (in shares) | (92,045) | ||
| Ending balance (in shares) | 561,407 | 774,475 | |
| Weighted-Average Grant Date Fair Value | |||
| Beginning balance (in dollars per share) | $ 8.96 | ||
| Granted (in dollars per share) | 12.91 | ||
| Vested (in dollars per share) | 7.89 | ||
| Forfeited (in dollars per share) | 11.14 | ||
| Ending balance (in dollars per share) | $ 14.00 | $ 8.96 | |
Share-based Compensation - Service-Based Awards, Additional disclosures (Details) - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Service-Based Awards, Additional disclosures [Abstract] | |||
| Weighted average per share fair value of service-based share grants (in dollars per share) | $ 13.05 | $ 10.11 | $ 12.58 |
Share-based Compensation - Share and performance-based compensation expense (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Share and performance-based compensation expense [Abstract] | |||
| Performance-based share expense | $ 32.6 | $ 9.3 | $ 2.0 |
| Service-based share expense | 14.4 | 6.1 | 4.6 |
| Total share-based compensation expense before income tax | 47.0 | 15.4 | 6.6 |
| Income tax | 0.0 | 0.0 | 0.0 |
| Total share-based compensation expense, net of income tax | $ 47.0 | $ 15.4 | $ 6.6 |
Earnings Per Share - Schedule of EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Earnings Per Share [Abstract] | |||||||||
| Net income attributable to Century stockholders | $ 14.9 | $ (4.6) | $ 29.7 | $ 47.3 | $ (2.5) | $ 246.8 | $ 41.8 | $ 336.8 | $ (43.1) |
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 1.8 | 17.9 | $ 0.0 |
| Amount allocated to common stockholders | 100.00% | ||||||||
| Basic EPS: | |||||||||
| Net income allocated to common stockholders | $ 14.1 | $ (4.6) | $ 28.2 | $ 44.8 | $ (2.5) | $ 233.6 | $ 40.0 | $ 318.9 | $ (43.1) |
| Net income allocated to common stockholders (in shares) | 94.2 | 92.8 | 92.4 | ||||||
| Net income allocated to common stockholders (in dollars per share) | $ 0.42 | $ 3.44 | $ (0.47) | ||||||
| Effect of Dilutive Securities | |||||||||
| Share-based compensation | $ 0.0 | $ 0.0 | |||||||
| Share-based compensation (in shares) | 1.1 | 1.0 | |||||||
| Convertible senior notes | $ 2.7 | ||||||||
| Convertible senior notes (in shares) | 4.6 | ||||||||
| Diluted EPS: | |||||||||
| Net income allocated to common stockholders | $ 40.0 | $ 321.6 | $ (43.1) | ||||||
| Net income allocated to common stockholders (in shares) | 95.3 | 98.4 | 92.4 | ||||||
| Net income allocated to common stockholders (in dollars per share) | $ 0.42 | $ 3.27 | $ (0.47) | ||||||
Earnings Per Share - Securities Excluded (Details) - shares shares in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Share-based compensation | |||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
| Share based compensation (in shares) | 0.6 | 0.6 | 1.0 |
| Convertible preferred shares | |||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
| Share based compensation (in shares) | 4.1 | 5.2 | 5.4 |
| Convertible senior notes | |||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
| Share based compensation (in shares) | 4.6 | 0.0 | 4.6 |
Income Taxes - Components of Pre-tax Book Income (Loss) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Income Tax Disclosure [Abstract] | |||
| U.S. | $ 167.4 | $ 335.5 | $ 78.0 |
| Foreign | (164.7) | (25.7) | (149.1) |
| Income (loss) before income taxes | $ 2.7 | $ 309.8 | $ (71.1) |
Income Taxes - Significant Components of Income Tax Expense (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Current: | |||
| U.S. federal current expense (benefit) | $ (0.2) | $ 0.0 | $ 0.5 |
| State current expense (benefit) | 0.4 | 0.0 | 0.0 |
| Foreign current expense (benefit) | 0.4 | 4.9 | 15.8 |
| Total current expense (benefit) | 0.6 | 4.9 | 16.3 |
| Deferred: | |||
| U.S. federal deferred benefit | 0.0 | 0.0 | (0.3) |
| State deferred benefit | 0.0 | 0.0 | (0.1) |
| Foreign deferred tax (benefit) expense | (13.7) | (1.7) | (30.5) |
| Total deferred (benefit) expense | (13.7) | (1.7) | (30.9) |
| Total income tax (benefit) expense | $ (13.1) | $ 3.2 | $ (14.6) |
Income Taxes - Reconciliation of statutory to effective income tax rate (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Amount | |||
| Statutory U.S. federal income tax rate | $ 0.6 | ||
| State income taxes, net of related federal income tax benefit | 0.3 | ||
| Effect of cross border tax laws | (0.1) | ||
| Effect of changes in tax laws or rates enacted in the period | 0.0 | ||
| Nontaxable advanced manufacturing production credit income | (18.6) | ||
| Executive compensation | 6.6 | ||
| Stock compensation excess tax benefits | (4.3) | ||
| Changes in unrecognized tax benefits | 0.1 | ||
| Total income tax (benefit) expense | $ (13.1) | $ 3.2 | $ (14.6) |
| Percent | |||
| Statutory U.S. federal income tax rate | 21.00% | 21.00% | 21.00% |
| State taxes, net of Federal benefit | 10.50% | 0.00% | (0.10%) |
| Valuation allowance | (11.60%) | 3.40% | |
| Net operating loss expiration and remeasurement | 3.00% | (7.50%) | |
| Nondeductible items | 2.00% | (0.20%) | |
| Other adjustments | 0.20% | (2.60%) | |
| Foreign earnings taxed at different rates than U.S. | 0.00% | 1.90% | |
| Effect of cross border tax laws | (4.50%) | ||
| Effect of changes in tax laws or rates enacted in the period | 0.00% | (0.50%) | (0.30%) |
| Nontaxable advanced manufacturing production credit income | (683.50%) | ||
| Executive compensation | 242.40% | ||
| Stock compensation excess tax benefits | (156.50%) | ||
| Foreign dividends and inclusions | 0.50% | (12.00%) | |
| Filing differences | 9.20% | 0.60% | |
| Changes in uncertain tax reserves | 2.70% | 0.20% | (1.20%) |
| Advanced Manufacturing Production Credit | (6.30%) | 17.50% | |
| Bargain Purchase gain | (0.167) | 0 | |
| Effective tax rate | (482.70%) | 1.00% | 20.50% |
| Iceland | |||
| Amount | |||
| Valuation allowance | $ (4.5) | ||
| Net operating loss expiration and remeasurement | 4.5 | ||
| Nondeductible interest | 8.5 | ||
| Nondeductible items | 2.4 | ||
| Fixed asset remeasurement | 0.6 | ||
| Other adjustments | $ 1.0 | ||
| Percent | |||
| Valuation allowance | (165.00%) | ||
| Net operating loss expiration and remeasurement | 163.80% | ||
| Nondeductible interest | 314.00% | ||
| Nondeductible items | 88.50% | ||
| Fixed asset remeasurement | 23.70% | ||
| Other adjustments | 35.70% | ||
| Netherlands | |||
| Amount | |||
| Other adjustments | $ (0.3) | ||
| Nontaxable items | $ (2.4) | ||
| Percent | |||
| Other adjustments | (12.00%) | ||
| Nontaxable items | (88.50%) | ||
| Jamaica | |||
| Amount | |||
| Valuation allowance | $ 5.2 | ||
| Nondeductible items | 3.6 | ||
| Minority interest | 5.5 | ||
| Federal statutory rate difference | $ (1.1) | ||
| Percent | |||
| Valuation allowance | 189.90% | ||
| Nondeductible items | 131.00% | ||
| Minority interest | 200.70% | ||
| Foreign earnings taxed at different rates than U.S. | (41.50%) | ||
| United States | |||
| Amount | |||
| Valuation allowance | $ (11.7) | ||
| Other adjustments | (0.2) | ||
| Nontaxable items | $ (8.8) | ||
| Percent | |||
| Valuation allowance | (429.90%) | ||
| Other adjustments | (2.40%) | ||
| Nontaxable items | (322.80%) | ||
Income Taxes - Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
||||||
| Tax Credit Carryforward [Line Items] | |||||||||||||||
| Effective tax rate | (482.70%) | 1.00% | 20.50% | ||||||||||||
| Reduction in cost of goods sold | $ (557.3) | $ (594.5) | $ (576.6) | $ (462.2) | $ (545.3) | $ (476.5) | $ (2,271.5) | [1] | $ (2,048.3) | [1] | $ (2,097.8) | [1] | |||
| Reduction in selling, general and administrative expenses | (79.9) | (56.8) | (44.3) | ||||||||||||
| Valuation allowance | 471.0 | 504.4 | |||||||||||||
| Unrecognized tax benefits | 3.6 | 3.5 | $ 3.0 | $ 2.2 | |||||||||||
| Inflation Reduction Act | |||||||||||||||
| Tax Credit Carryforward [Line Items] | |||||||||||||||
| Reduction in cost of goods sold | 89.1 | 89.7 | |||||||||||||
| Reduction in selling, general and administrative expenses | $ 3.8 | $ 2.9 | |||||||||||||
| |||||||||||||||
Income Taxes - Income Tax Paid (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Effective Income Tax Rate Reconciliation [Line Items] | |||
| Federal | $ 0.0 | ||
| State | 0.5 | ||
| Total | 4.8 | $ 14.5 | $ 5.9 |
| Iceland | |||
| Effective Income Tax Rate Reconciliation [Line Items] | |||
| Foreign | 2.3 | ||
| Netherlands | |||
| Effective Income Tax Rate Reconciliation [Line Items] | |||
| Foreign | $ 2.0 | ||
Income Taxes - Significant Components of our deferred tax assets & liabilities (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Deferred tax assets: | ||
| Accrued postretirement benefit cost | $ 18.2 | $ 30.1 |
| Net operating losses | 465.0 | 473.3 |
| Disallowed interest expense | 31.9 | 37.1 |
| Derivative and hedging contracts | 11.2 | 0.1 |
| Other | 28.6 | 29.4 |
| Total deferred tax assets | 554.9 | 570.0 |
| Valuation allowance | (471.0) | (504.4) |
| Net deferred tax assets | 83.9 | 65.6 |
| Deferred tax liabilities: | ||
| Fixed asset book over tax basis | (119.3) | (115.9) |
| Foreign basis differences | 0.1 | 0.6 |
| Other | (22.0) | (21.4) |
| Total deferred tax liabilities | (141.2) | (136.7) |
| Net deferred tax liability | $ (57.3) | $ (71.1) |
Income Taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Movement in Valuation Allowances and Reserves [Roll Forward] | |||
| Balance, valuation allowance | $ 504.4 | $ 537.6 | $ 487.9 |
| Expiration of net operating losses | (5.2) | (6.1) | (7.2) |
| Other change in valuation allowance | (28.2) | (27.1) | 56.9 |
| Balance, valuation allowance | $ 471.0 | $ 504.4 | $ 537.6 |
Income Taxes - Net Operating Losses Carryforwards (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Federal | ||
| Operating Loss Carryforwards [Line Items] | ||
| Operating loss carryforwards | $ 1,544.9 | $ 1,571.2 |
| State | ||
| Operating Loss Carryforwards [Line Items] | ||
| Operating loss carryforwards | 1,168.1 | 1,163.5 |
| Foreign | ||
| Operating Loss Carryforwards [Line Items] | ||
| Operating loss carryforwards | $ 377.7 | $ 342.2 |
Income Taxes - Gross Unrecognized Tax Positions (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] | |||
| Balance as of January 1, | $ 3.5 | $ 3.0 | $ 2.2 |
| Additions based on tax positions related to the current year | 0.1 | 0.6 | 1.3 |
| Decreases due to lapse of applicable statute of limitations | 0.0 | (0.1) | (0.5) |
| Balance as of December 31, | $ 3.6 | $ 3.5 | $ 3.0 |
Commitments and Contingencies (Details) $ in Millions |
1 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
|
Oct. 01, 2021
USD ($)
|
Aug. 18, 2017
USD ($)
|
Sep. 30, 2017
USD ($)
|
Dec. 31, 2025
USD ($)
laborUnion
MW
|
Dec. 31, 2013
USD ($)
|
|
| Labor Commitments [Abstract] | |||||
| Percentage of total work force in union | 55.00% | ||||
| Percentage of Grundartangi work force represented by the labor unions | 84.00% | ||||
| Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | laborUnion | 5 | ||||
| Percentage of domestic based work force represented by a union | 36.00% | ||||
| Percentage of foreign work force represented by union | 0.62 | ||||
| Contingent consideration, accrued interest and principal | $ 33.7 | ||||
| E.ON Contingent Obligation | Long-term Debt | |||||
| Labor Commitments [Abstract] | |||||
| Stated interest rate, percentage | 10.94% | ||||
| Netherlands | |||||
| Labor Commitments [Abstract] | |||||
| Percentage of total work force in union | 100.00% | ||||
| Pension Benefit Guarantee Corporation | |||||
| PBGC Settlement [Abstract] | |||||
| Required pension contributions above minimum | $ 17.4 | ||||
| Pension contributions, amended term, annual contribution | $ 2.4 | ||||
| Pension contributions, amended term, total contribution | $ 9.6 | ||||
| Pension contributions, term | 4 years | ||||
| Kenergy | Century Marketer, LLC | |||||
| Power Contingencies [Abstract] | |||||
| Extension term | 1 year | ||||
| Required termination period | 1 year | ||||
| Sebree | Kenergy | |||||
| Power Contingencies [Abstract] | |||||
| Extension term | 1 year | ||||
| Required termination period | 1 year | ||||
| Santee Cooper | |||||
| Power Contingencies [Abstract] | |||||
| Power agreement, power supply, percentage | 100.00% | ||||
| Grundartangi - HS, Landsvirkjun | |||||
| Power Contingencies [Abstract] | |||||
| Power currently available under the power purchase agreement, available (in megawatts) | MW | 545 | ||||
| Grundartangi - Landsvirkjun | |||||
| Power Contingencies [Abstract] | |||||
| Power currently available under the power purchase agreement, available (in megawatts) | MW | 25 | ||||
| Ravenswood Retiree Medical Benefits Changes | |||||
| Ravenswood litigation [Abstract] | |||||
| Litigation settlement amount | $ 23.0 | ||||
| Ravenswood litigation settlement installment period | 10 years | ||||
| Litigation payment to trust | $ 5.0 | ||||
| Gain (loss) related to litigation settlement | 5.5 | ||||
| Loss contingency accrual | $ 12.5 | ||||
| Litigation settlement, annual installment | $ 2.0 | ||||
| Litigation settlement installment period | 9 years | ||||
| Other current liabilities | $ 1.9 | ||||
Asset Retirement Obligations (Details) - USD ($) $ in Millions |
12 Months Ended | |||||
|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2023 |
|
| Asset Retirement Obligation [Roll Forward] | ||||||
| Beginning balance | $ 88.4 | $ 51.1 | ||||
| Additional ARO liabilities incurred | 3.4 | 6.7 | ||||
| ARO liabilities settled | (8.5) | (4.6) | ||||
| Accretion expense | 3.4 | 2.5 | ||||
| Acquired ARO liabilities | 0.0 | 21.9 | ||||
| Revisions in estimated cash flows | (3.3) | 10.8 | ||||
| Ending balance | 83.4 | 88.4 | ||||
| Current portion of asset retirement obligations | 8.1 | 7.1 | ||||
| Asset retirement obligations - less current portion | $ 75.3 | $ 81.3 | $ 83.3 | $ 82.5 | $ 85.1 | $ 63.0 |
Business Segments - Narrative (Details) |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2025
segment
smelter
|
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Segment, Reconciliation of Other Items from Segments to Consolidated [Line Items] | |||
| Number of smelters | smelter | 3 | ||
| Number of operating segments | 1 | ||
| Number of reportable segments | 1 | ||
| Customer Concentration Risk | Sales Revenue | Glencore | |||
| Segment, Reconciliation of Other Items from Segments to Consolidated [Line Items] | |||
| Concentration risk, percentage | 10.00% | 10.00% | 10.00% |
Business Segments - Reconciliation of Net Income (Loss) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Total net sales | $ 2,527.9 | $ 2,220.3 | $ 2,185.4 | ||||||
| Selling, general and administrative expenses | (79.9) | (56.8) | (44.3) | ||||||
| Other operating expenses - net | (18.4) | (6.8) | (15.8) | ||||||
| Interest income | 9.2 | 2.1 | 2.0 | ||||||
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.0 | 61.8 | ||||||
| Loss on early extinguishment of debt | (7.7) | 0.0 | 0.0 | ||||||
| Bargain purchase gain | 0.0 | 245.9 | 0.0 | ||||||
| Other expense - net | (14.5) | (5.5) | (3.3) | ||||||
| Income tax benefit (expense) | 13.1 | (3.2) | 14.6 | ||||||
| Equity in earnings (losses) of joint ventures | 0.0 | 0.1 | (0.1) | ||||||
| Net income (loss) | $ 8.2 | $ (11.7) | $ 22.4 | $ 37.4 | $ (11.6) | $ 241.2 | 15.8 | 306.7 | (56.6) |
| Nonrelated Party | |||||||||
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Total net sales | 1,162.4 | 908.2 | 573.3 | ||||||
| Interest expense | (41.9) | (36.4) | (33.7) | ||||||
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.5 | (62.4) | ||||||
| Related Party | |||||||||
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Total net sales | 1,365.5 | 1,312.1 | 1,612.1 | ||||||
| Interest expense | (5.8) | (6.7) | (1.8) | ||||||
| Net gain (loss) on forward and derivative contracts | 0.0 | (0.5) | 0.6 | ||||||
| Reportable Segment | |||||||||
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Total net sales | 2,527.9 | 2,220.3 | 2,185.4 | ||||||
| Segment Cost of goods sold | (2,256.7) | (2,042.7) | (2,099.7) | ||||||
| IRA Credit | 89.1 | 89.7 | 56.5 | ||||||
| Lower of cost or NRV inventory adjustment | (8.6) | 4.2 | 27.5 | ||||||
| Property and equipment expense | (95.3) | (99.5) | (82.1) | ||||||
| Selling, general and administrative expenses | (79.9) | (56.8) | (44.3) | ||||||
| Other operating expenses - net | (18.4) | (6.8) | (15.8) | ||||||
| Interest income | 9.2 | 2.1 | 2.0 | ||||||
| Loss on early extinguishment of debt | (7.7) | 0.0 | 0.0 | ||||||
| Bargain purchase gain | 0.0 | 245.9 | 0.0 | ||||||
| Other expense - net | (14.5) | (5.5) | (3.3) | ||||||
| Income tax benefit (expense) | 13.1 | (3.2) | 14.6 | ||||||
| Equity in earnings (losses) of joint ventures | 0.0 | 0.1 | (0.1) | ||||||
| Net income (loss) | 15.8 | 306.7 | (56.6) | ||||||
| Reportable Segment | Nonrelated Party | |||||||||
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Interest expense | (41.9) | (36.4) | (33.7) | ||||||
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.5 | (62.4) | ||||||
| Reportable Segment | Related Party | |||||||||
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] | |||||||||
| Interest expense | (5.8) | (6.7) | (1.8) | ||||||
| Net gain (loss) on forward and derivative contracts | $ 0.0 | $ (0.5) | $ 0.6 | ||||||
Business Segments - Long-Lived Assets (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| United States | |||
| Revenues from External Customers and Long-Lived Assets [Line Items] | |||
| Long-lived assets | $ 232.1 | $ 233.6 | $ 219.1 |
| Iceland | |||
| Revenues from External Customers and Long-Lived Assets [Line Items] | |||
| Long-lived assets | 506.5 | 526.4 | 529.4 |
| Jamaica | |||
| Revenues from External Customers and Long-Lived Assets [Line Items] | |||
| Long-lived assets | 449.5 | 435.3 | 458.1 |
| Other | |||
| Revenues from External Customers and Long-Lived Assets [Line Items] | |||
| Long-lived assets | $ 48.6 | $ 50.6 | $ 55.1 |
Derivatives - Narrative (Details) |
12 Months Ended | |
|---|---|---|
|
Dec. 31, 2025
USD ($)
Boe
MWh
t
|
Dec. 31, 2024
USD ($)
|
|
| Supply Commitment [Line Items] | ||
| Restricted cash | $ | $ 0 | $ 0 |
| Fixed to Variable London Metals Exchange Swap | ||
| Supply Commitment [Line Items] | ||
| Open position to offset fixed prices | 48,400 | |
| Fixed to Variable Midwest Premium Swap | ||
| Supply Commitment [Line Items] | ||
| Open position to offset fixed prices | 89,800 | |
| Fixed to Floating Swap | ||
| Supply Commitment [Line Items] | ||
| Open position to offset fixed prices | 0 | |
| HFO Price Swaps | ||
| Supply Commitment [Line Items] | ||
| Derivative liability, energy | Boe | 225,000 | |
| Indiana Hub Power Price Swaps | ||
| Supply Commitment [Line Items] | ||
| Derivative liability, energy | MWh | 884,712 |
Derivative - Assets and Liabilities (Details) - USD ($) |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|
| Derivative [Line Items] | |||
| Due to affiliates | $ 109,300,000 | $ 101,400,000 | |
| Related Party | |||
| Derivative [Line Items] | |||
| Due to affiliates | $ 70,800,000 | 109,300,000 | |
| Commodity Contract | Related Party | |||
| Derivative [Line Items] | |||
| Due to affiliates | 0 | 0 | |
| Not Designated as Hedging Instrument | Commodity Contract | |||
| Derivative [Line Items] | |||
| Asset Fair Value | 1,900,000 | 4,500,000 | |
| Liability Fair Value | $ 66,000,000.0 | $ 4,400,000 |
Derivative - Net Gain (Loss) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | $ (94.7) | $ 2.0 | $ 61.8 |
| Nonrelated Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | (94.7) | 1.5 | 61.2 |
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.5 | (62.4) |
| Related Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | 0.0 | 0.5 | 0.6 |
| Net gain (loss) on forward and derivative contracts | 0.0 | (0.5) | 0.6 |
| Commodity Contract | Nonrelated Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | (94.7) | 1.6 | 62.9 |
| Commodity Contract | Related Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | 0.0 | 0.5 | 0.6 |
| Foreign Exchange Contract | Nonrelated Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | 0.0 | (0.1) | (1.7) |
| Foreign Exchange Contract | Related Party | |||
| Derivative [Line Items] | |||
| Net gain (loss) on forward and derivative contracts | $ 0.0 | $ 0.0 | $ 0.0 |
Variable Interest Entity - Narrative (Details) - Jamalco |
Dec. 31, 2025 |
Dec. 31, 2023 |
|---|---|---|
| Variable Interest Entity [Line Items] | ||
| Ownership percentage | 55.00% | 55.00% |
| Percentage of output retained, utilized, or sold by the company | 100.00% | |
| Percentage of operations reflected in cash flows | 100.00% | |
| Government Of Jamaica | ||
| Variable Interest Entity [Line Items] | ||
| Glencore beneficial ownership | 45.00% |
Variable Interest Entity - Schedule of Consolidated VIE's Assets and Liabilities (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2023 |
|---|---|---|---|---|---|---|---|---|---|
| ASSETS | |||||||||
| Cash and cash equivalents | $ 134.2 | $ 32.9 | $ 88.8 | ||||||
| Accounts receivable - net | 109.9 | 75.8 | 53.7 | ||||||
| Inventories | 519.6 | 539.0 | 477.0 | ||||||
| Prepaid and other current assets | 24.4 | 28.3 | 27.5 | ||||||
| Total current assets | 1,031.3 | $ 1,046.9 | $ 807.4 | $ 829.6 | 810.9 | $ 804.0 | $ 729.3 | $ 782.7 | 767.1 |
| Property, plant and equipment - net | 1,167.6 | 1,139.2 | 1,150.8 | 1,142.0 | 1,149.8 | 1,129.7 | 1,129.5 | 1,137.9 | 1,184.2 |
| Other assets | 70.4 | 72.0 | 70.6 | 70.2 | 88.9 | 125.7 | 98.8 | 85.7 | 77.5 |
| TOTAL | 2,269.3 | 2,321.9 | 2,142.3 | 2,132.8 | 2,120.0 | 2,059.4 | 1,957.6 | 2,006.3 | 2,028.8 |
| LIABILITIES | |||||||||
| Accounts payable, trade | 187.2 | 187.3 | 249.5 | ||||||
| Accrued compensation and benefits | 74.4 | 53.4 | 45.2 | 41.6 | 50.8 | 130.3 | 131.3 | 132.5 | 38.7 |
| Due to affiliates | 109.3 | 101.4 | |||||||
| Accrued and other current liabilities | 35.6 | 76.8 | 48.0 | 39.2 | 44.6 | 50.9 | |||
| Total current liabilities | 523.6 | 591.5 | 447.5 | 443.6 | 467.3 | 763.6 | |||
| Accrued benefits costs - less current portion | 97.7 | 136.3 | 142.3 | 143.8 | 144.9 | 69.5 | 62.1 | 63.2 | 129.4 |
| Other liabilities | 104.9 | 92.6 | 66.3 | ||||||
| Asset retirement obligations - less current portion | 75.3 | 83.3 | 82.5 | 85.1 | 81.3 | 63.0 | |||
| Total noncurrent liabilities | 815.8 | $ 871.6 | $ 847.4 | $ 851.6 | 847.3 | $ 822.6 | $ 817.5 | $ 817.9 | $ 762.0 |
| Variable Interest Entity, Primary Beneficiary | |||||||||
| ASSETS | |||||||||
| Cash and cash equivalents | 4.6 | 17.4 | |||||||
| Accounts receivable - net | 0.1 | 1.1 | |||||||
| Inventories | 116.6 | 109.8 | |||||||
| Prepaid and other current assets | 8.9 | 2.0 | |||||||
| Total current assets | 130.2 | 130.3 | |||||||
| Property, plant and equipment - net | 426.3 | 403.6 | |||||||
| Other assets | 12.0 | 24.1 | |||||||
| TOTAL | 568.5 | 558.0 | |||||||
| LIABILITIES | |||||||||
| Accounts payable, trade | 49.0 | 39.1 | |||||||
| Accrued compensation and benefits | 11.7 | 9.5 | |||||||
| Accrued and other current liabilities | 8.2 | 9.7 | |||||||
| Total current liabilities | 86.2 | 107.9 | |||||||
| Accrued benefits costs - less current portion | 32.2 | 32.2 | |||||||
| Other liabilities | 62.1 | 66.7 | |||||||
| Asset retirement obligations - less current portion | 46.6 | 54.8 | |||||||
| Total noncurrent liabilities | 140.9 | 153.7 | |||||||
| TOTAL | 227.1 | 261.6 | |||||||
| Variable Interest Entity, Primary Beneficiary | Related Party | |||||||||
| LIABILITIES | |||||||||
| Due to affiliates | $ 17.3 | $ 49.6 |
Restatement of Previously Issued Financial Statements - Consolidated Statements of Operations (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
||||||
| Net sales | ||||||||||||||
| Net sales | $ 2,527.9 | $ 2,220.3 | $ 2,185.4 | |||||||||||
| Cost of Goods Sold | $ 557.3 | $ 594.5 | $ 576.6 | $ 462.2 | $ 545.3 | $ 476.5 | 2,271.5 | [1] | 2,048.3 | [1] | 2,097.8 | [1] | ||
| Gross profit | 74.9 | 33.6 | 57.3 | 76.9 | 15.5 | 13.0 | 256.4 | 172.0 | 87.6 | |||||
| Selling, general and administrative expenses | 79.9 | 56.8 | 44.3 | |||||||||||
| Other operating expense (income), net | 18.4 | 6.8 | 15.8 | |||||||||||
| Operating income | 55.9 | 18.1 | 42.8 | 58.9 | 1.5 | (1.6) | 158.1 | 108.4 | 27.5 | |||||
| Interest income | 9.2 | 2.1 | 2.0 | |||||||||||
| Net gain (loss) on forward and derivative contracts | (94.7) | 2.0 | 61.8 | |||||||||||
| Bargain purchase gain | 0.0 | 245.9 | 0.0 | |||||||||||
| Other income, net | (14.5) | (5.5) | (3.3) | |||||||||||
| Income (loss) before income taxes | 7.1 | (13.0) | 24.0 | 39.4 | (11.1) | 241.7 | 2.7 | 309.8 | (71.1) | |||||
| Income tax benefit (expense) | 13.1 | (3.2) | 14.6 | |||||||||||
| Income (loss) before equity in earnings of joint ventures | 15.8 | 306.6 | (56.5) | |||||||||||
| Equity in earnings (losses) of joint ventures | 0.0 | 0.1 | (0.1) | |||||||||||
| Net income (loss) | 8.2 | (11.7) | 22.4 | 37.4 | (11.6) | 241.2 | 15.8 | 306.7 | (56.6) | |||||
| Net loss attributable to noncontrolling interests | (6.7) | (7.1) | (7.3) | (9.9) | (9.1) | (5.6) | (26.0) | (30.1) | (13.5) | |||||
| Net income (loss) attributable to Century stockholders | 14.9 | (4.6) | 29.7 | 47.3 | (2.5) | 246.8 | 41.8 | 336.8 | (43.1) | |||||
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 1.8 | 17.9 | 0.0 | |||||
| Net income (loss) allocated to common stockholders | 14.1 | (4.6) | 28.2 | 44.8 | (2.5) | 233.6 | 40.0 | 318.9 | (43.1) | |||||
| Related Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 1,365.5 | 1,312.1 | 1,612.1 | |||||||||||
| Cost of Goods Sold | 294.0 | 277.9 | 181.4 | |||||||||||
| Interest expense | (5.8) | (6.7) | (1.8) | |||||||||||
| Net gain (loss) on forward and derivative contracts | 0.0 | (0.5) | 0.6 | |||||||||||
| Nonrelated Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 1,162.4 | 908.2 | 573.3 | |||||||||||
| Interest expense | (41.9) | (36.4) | (33.7) | |||||||||||
| Net gain (loss) on forward and derivative contracts | $ (94.7) | 2.5 | (62.4) | |||||||||||
| As Previously Reported | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 2,220.3 | 2,185.4 | ||||||||||||
| Cost of Goods Sold | 554.9 | 591.9 | 573.3 | 457.3 | 540.4 | 473.0 | 2,035.3 | 2,093.5 | ||||||
| Gross profit | 77.3 | 36.2 | 60.6 | 81.8 | 20.4 | 16.5 | 185.0 | 91.9 | ||||||
| Selling, general and administrative expenses | 56.8 | 44.3 | ||||||||||||
| Other operating expense (income), net | 6.8 | 15.8 | ||||||||||||
| Operating income | 58.3 | 20.7 | 46.1 | 63.8 | 6.4 | 1.9 | 121.4 | 31.8 | ||||||
| Interest income | 2.1 | 2.0 | ||||||||||||
| Bargain purchase gain | 245.9 | 0.0 | ||||||||||||
| Other income, net | (4.5) | (3.3) | ||||||||||||
| Income (loss) before income taxes | 9.5 | (10.4) | 27.3 | 44.3 | (6.2) | 245.2 | 323.8 | (66.8) | ||||||
| Income tax benefit (expense) | (3.2) | 14.6 | ||||||||||||
| Income (loss) before equity in earnings of joint ventures | 320.6 | (52.2) | ||||||||||||
| Equity in earnings (losses) of joint ventures | 0.1 | (0.1) | ||||||||||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | ||||||
| Net loss attributable to noncontrolling interests | (4.3) | (4.5) | (4.0) | (5.0) | (4.2) | (2.1) | (16.1) | (9.2) | ||||||
| Net income (loss) attributable to Century stockholders | 14.9 | (4.6) | 29.7 | 47.3 | (2.5) | 246.8 | 336.8 | (43.1) | ||||||
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 17.9 | 0.0 | ||||||
| Net income (loss) allocated to common stockholders | 14.1 | (4.6) | 28.2 | 44.8 | (2.5) | 233.6 | 318.9 | (43.1) | ||||||
| As Previously Reported | Related Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 1,312.1 | 1,612.1 | ||||||||||||
| Interest expense | (6.7) | (1.8) | ||||||||||||
| Net gain (loss) on forward and derivative contracts | (0.5) | 0.6 | ||||||||||||
| As Previously Reported | Nonrelated Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 908.2 | 573.3 | ||||||||||||
| Interest expense | (36.4) | (33.7) | ||||||||||||
| Net gain (loss) on forward and derivative contracts | 2.5 | (62.4) | ||||||||||||
| Restatement Impacts | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 0.0 | 0.0 | ||||||||||||
| Cost of Goods Sold | 2.4 | 2.6 | 3.3 | 4.9 | 4.9 | 3.5 | 13.0 | 4.3 | ||||||
| Gross profit | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (13.0) | (4.3) | ||||||
| Selling, general and administrative expenses | 0.0 | 0.0 | ||||||||||||
| Other operating expense (income), net | 0.0 | 0.0 | ||||||||||||
| Operating income | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (13.0) | (4.3) | ||||||
| Interest income | 0.0 | 0.0 | ||||||||||||
| Bargain purchase gain | 0.0 | 0.0 | ||||||||||||
| Other income, net | (1.0) | 0.0 | ||||||||||||
| Income (loss) before income taxes | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Income tax benefit (expense) | 0.0 | 0.0 | ||||||||||||
| Income (loss) before equity in earnings of joint ventures | (14.0) | (4.3) | ||||||||||||
| Equity in earnings (losses) of joint ventures | 0.0 | 0.0 | ||||||||||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Net loss attributable to noncontrolling interests | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Net income (loss) attributable to Century stockholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | ||||||
| Less: Net income allocated to participating securities | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | ||||||
| Net income (loss) allocated to common stockholders | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | 0.0 | 0.0 | ||||||
| Restatement Impacts | Related Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 0.0 | 0.0 | ||||||||||||
| Interest expense | 0.0 | 0.0 | ||||||||||||
| Net gain (loss) on forward and derivative contracts | 0.0 | 0.0 | ||||||||||||
| Restatement Impacts | Nonrelated Party | ||||||||||||||
| Net sales | ||||||||||||||
| Net sales | 0.0 | 0.0 | ||||||||||||
| Interest expense | 0.0 | 0.0 | ||||||||||||
| Net gain (loss) on forward and derivative contracts | $ 0.0 | $ 0.0 | ||||||||||||
| ||||||||||||||
Restatement of Previously Issued Financial Statements - Consolidated Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Comprehensive income (loss): | |||||||||
| Net income (loss) | $ 8.2 | $ (11.7) | $ 22.4 | $ 37.4 | $ (11.6) | $ 241.2 | $ 15.8 | $ 306.7 | $ (56.6) |
| Other comprehensive income (loss) before income tax effect: | |||||||||
| Net gain on foreign currency cash flow hedges reclassified as income | (0.1) | (0.2) | (0.1) | ||||||
| Defined benefit plans and other postretirement benefits: | |||||||||
| Net loss arising during the period | 42.0 | (13.1) | (19.2) | ||||||
| Amortization of prior service benefit during the period | 0.2 | 0.2 | 0.1 | ||||||
| Amortization of net gain (loss) during the period | 6.0 | 6.5 | 6.2 | ||||||
| Other comprehensive income (loss) before income tax effect | 48.1 | (6.6) | (13.0) | ||||||
| Income tax effect | 0.0 | 0.0 | 0.0 | ||||||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | 48.1 | (6.6) | (13.0) |
| Comprehensive income (loss) | 63.9 | 300.1 | (69.6) | ||||||
| Comprehensive loss attributable to noncontrolling interests | (26.0) | (31.3) | (22.6) | ||||||
| Comprehensive income (loss) attributable to Century stockholders | $ 89.9 | 331.4 | (47.0) | ||||||
| As Previously Reported | |||||||||
| Comprehensive income (loss): | |||||||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | |
| Other comprehensive income (loss) before income tax effect: | |||||||||
| Net gain on foreign currency cash flow hedges reclassified as income | (0.2) | (0.1) | |||||||
| Defined benefit plans and other postretirement benefits: | |||||||||
| Net loss arising during the period | (11.9) | (10.1) | |||||||
| Amortization of prior service benefit during the period | 0.2 | 0.1 | |||||||
| Amortization of net gain (loss) during the period | 6.5 | 6.2 | |||||||
| Other comprehensive income (loss) before income tax effect | (5.4) | (3.9) | |||||||
| Income tax effect | 0.0 | 0.0 | |||||||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | (5.4) | (3.9) | |
| Comprehensive income (loss) | 315.3 | (56.2) | |||||||
| Comprehensive loss attributable to noncontrolling interests | (16.1) | (9.2) | |||||||
| Comprehensive income (loss) attributable to Century stockholders | 331.4 | (47.0) | |||||||
| Restatement Impacts | |||||||||
| Comprehensive income (loss): | |||||||||
| Net income (loss) | $ (2.4) | $ (2.6) | $ (3.3) | $ (4.9) | $ (4.9) | $ (3.5) | (14.0) | (4.3) | |
| Other comprehensive income (loss) before income tax effect: | |||||||||
| Net gain on foreign currency cash flow hedges reclassified as income | 0.0 | 0.0 | |||||||
| Defined benefit plans and other postretirement benefits: | |||||||||
| Net loss arising during the period | (1.2) | (9.1) | |||||||
| Amortization of prior service benefit during the period | 0.0 | 0.0 | |||||||
| Amortization of net gain (loss) during the period | 0.0 | 0.0 | |||||||
| Other comprehensive income (loss) before income tax effect | (1.2) | (9.1) | |||||||
| Income tax effect | 0.0 | 0.0 | |||||||
| Other comprehensive income (loss) | (1.2) | (9.1) | |||||||
| Comprehensive income (loss) | (15.2) | (13.4) | |||||||
| Comprehensive loss attributable to noncontrolling interests | (15.2) | (13.4) | |||||||
| Comprehensive income (loss) attributable to Century stockholders | $ 0.0 | $ 0.0 | |||||||
Restatement of Previously Issued Financial Statements - Consolidated Balance Sheets (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
|---|---|---|---|---|---|---|---|---|---|---|
| ASSETS | ||||||||||
| Cash and cash equivalents | $ 134.2 | $ 32.9 | $ 88.8 | |||||||
| Restricted cash | 1.4 | 2.8 | 1.5 | |||||||
| Accounts receivable - net | 109.9 | 75.8 | 53.7 | |||||||
| Non-trade receivables | 38.1 | $ 19.8 | $ 17.1 | $ 7.7 | 21.3 | $ 49.8 | $ 46.9 | $ 40.1 | 36.2 | |
| Manufacturing credit receivable | 172.6 | 81.5 | 59.3 | |||||||
| Inventories | 519.6 | 539.0 | 477.0 | |||||||
| Derivative assets | 1.5 | 4.2 | 2.9 | |||||||
| Prepaid and other current assets | 24.4 | 28.3 | 27.5 | |||||||
| Total current assets | 1,031.3 | 1,046.9 | 807.4 | 829.6 | 810.9 | 804.0 | 729.3 | 782.7 | 767.1 | |
| Property, plant and equipment - net | 1,167.6 | 1,139.2 | 1,150.8 | 1,142.0 | 1,149.8 | 1,129.7 | 1,129.5 | 1,137.9 | 1,184.2 | |
| Manufacturing credit receivable - less current portion | 0.0 | 70.4 | 0.0 | |||||||
| Other assets | 70.4 | 72.0 | 70.6 | 70.2 | 88.9 | 125.7 | 98.8 | 85.7 | 77.5 | |
| TOTAL | 2,269.3 | 2,321.9 | 2,142.3 | 2,132.8 | 2,120.0 | 2,059.4 | 1,957.6 | 2,006.3 | 2,028.8 | |
| LIABILITIES: | ||||||||||
| Accounts payable, trade | 187.2 | 187.3 | 249.5 | |||||||
| Accrued compensation and benefits | 74.4 | 53.4 | 45.2 | 41.6 | 50.8 | 130.3 | 131.3 | 132.5 | 38.7 | |
| Due to affiliates | 109.3 | 101.4 | ||||||||
| Accrued and other current liabilities | 35.6 | 76.8 | 48.0 | 39.2 | 44.6 | 50.9 | ||||
| Derivative liabilities | 58.2 | 4.4 | 1.4 | |||||||
| Deferred credit - preliminary bargain purchase gain | 273.4 | |||||||||
| Total current liabilities | 523.6 | 591.5 | 447.5 | 443.6 | 467.3 | 763.6 | ||||
| Accrued benefits costs - less current portion | 97.7 | 136.3 | 142.3 | 143.8 | 144.9 | 69.5 | 62.1 | 63.2 | 129.4 | |
| Other liabilities | 104.9 | 92.6 | 66.3 | |||||||
| Deferred Income Tax Liabilities, Net | 58.4 | 71.2 | 72.4 | |||||||
| Asset retirement obligations - less current portion | 75.3 | 83.3 | 82.5 | 85.1 | 81.3 | 63.0 | ||||
| Total noncurrent liabilities | 815.8 | 871.6 | 847.4 | 851.6 | 847.3 | 822.6 | 817.5 | 817.9 | 762.0 | |
| Commitments and Contingencies | ||||||||||
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Preferred stock | 0.0 | 0.0 | 0.0 | |||||||
| Common stock | 1.1 | 1.0 | 1.0 | |||||||
| Additional paid-in capital | 2,571.5 | 2,550.2 | 2,542.9 | |||||||
| Treasury stock, at cost | (86.3) | (86.3) | (86.3) | |||||||
| Accumulated other comprehensive loss | (55.2) | (103.3) | (97.9) | |||||||
| Accumulated deficit | (1,625.5) | (1,667.2) | (2,004.1) | |||||||
| Total Century shareholders’ equity | 805.6 | 694.4 | 355.6 | |||||||
| Noncontrolling interest | 124.3 | 117.0 | 123.0 | 111.5 | 111.0 | 112.4 | 110.5 | 118.0 | 147.6 | |
| Total equity | 929.9 | 858.8 | 847.4 | 837.8 | 805.4 | 764.5 | 712.0 | 719.5 | 503.2 | $ 399.3 |
| TOTAL | 2,269.3 | 2,321.9 | 2,142.3 | 2,132.8 | 2,120.0 | 2,059.4 | 1,957.6 | 2,006.3 | 2,028.8 | |
| Nonrelated Party | ||||||||||
| LIABILITIES: | ||||||||||
| Current maturities of long-term debt | 68.8 | 70.9 | 38.3 | |||||||
| Long-term debt | 479.5 | 447.3 | 430.9 | |||||||
| Related Party | ||||||||||
| ASSETS | ||||||||||
| Due from affiliates | 29.6 | 25.1 | 20.2 | |||||||
| LIABILITIES: | ||||||||||
| Due to affiliates | 70.8 | 109.3 | ||||||||
| Current maturities of long-term debt | 10.0 | |||||||||
| Long-term debt | $ 0.0 | 10.0 | ||||||||
| As Previously Reported | ||||||||||
| ASSETS | ||||||||||
| Cash and cash equivalents | 32.9 | 88.8 | ||||||||
| Restricted cash | 2.8 | 1.5 | ||||||||
| Accounts receivable - net | 75.8 | 53.7 | ||||||||
| Non-trade receivables | 0.0 | 0.0 | 0.0 | 13.2 | 52.7 | 53.5 | 38.5 | 36.2 | ||
| Manufacturing credit receivable | 81.5 | 59.3 | ||||||||
| Inventories | 539.0 | 477.0 | ||||||||
| Derivative assets | 4.2 | 2.9 | ||||||||
| Prepaid and other current assets | 28.3 | 27.5 | ||||||||
| Total current assets | 1,027.1 | 790.3 | 821.9 | 802.8 | 806.9 | 735.9 | 781.1 | 767.1 | ||
| Property, plant and equipment - net | 972.2 | 975.6 | 972.2 | 978.3 | 965.3 | 971.5 | 984.2 | 1,004.2 | ||
| Manufacturing credit receivable - less current portion | 70.4 | 0.0 | ||||||||
| Other assets | 71.1 | 69.6 | 69.3 | 87.9 | 124.7 | 97.8 | 84.6 | 75.2 | ||
| TOTAL | 2,134.2 | 1,949.0 | 1,954.5 | 1,939.4 | 1,896.9 | 1,805.2 | 1,849.9 | 1,846.5 | ||
| LIABILITIES: | ||||||||||
| Accounts payable, trade | 187.3 | 249.5 | ||||||||
| Accrued compensation and benefits | 52.4 | 44.2 | 40.6 | 49.8 | 119.2 | 120.2 | 121.3 | 38.1 | ||
| Due to affiliates | 109.3 | 101.4 | ||||||||
| Accrued and other current liabilities | 73.6 | 44.9 | 36.6 | 42.0 | 50.9 | |||||
| Derivative liabilities | 4.4 | 1.4 | ||||||||
| Deferred credit - preliminary bargain purchase gain | 273.4 | |||||||||
| Total current liabilities | 599.1 | 451.1 | 447.4 | 463.7 | 763.0 | |||||
| Accrued benefits costs - less current portion | 121.8 | 127.8 | 129.3 | 130.4 | 54.1 | 49.9 | 50.4 | 120.3 | ||
| Other liabilities | 92.6 | 66.3 | ||||||||
| Deferred Income Tax Liabilities, Net | 71.2 | 72.4 | ||||||||
| Asset retirement obligations - less current portion | 63.9 | 63.2 | 64.4 | 61.5 | 49.5 | |||||
| Total noncurrent liabilities | 837.7 | 813.6 | 816.4 | 813.0 | 796.1 | 794.2 | 793.9 | 739.4 | ||
| Commitments and Contingencies | ||||||||||
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Preferred stock | 0.0 | 0.0 | ||||||||
| Common stock | 1.0 | 1.0 | ||||||||
| Additional paid-in capital | 2,550.2 | 2,542.9 | ||||||||
| Treasury stock, at cost | (86.3) | (86.3) | ||||||||
| Accumulated other comprehensive loss | (103.3) | (97.9) | ||||||||
| Accumulated deficit | (1,667.2) | (2,004.1) | ||||||||
| Total Century shareholders’ equity | 694.4 | 355.6 | ||||||||
| Noncontrolling interest | (44.4) | (40.1) | (35.6) | (31.7) | (23.6) | (18.6) | (14.4) | (11.5) | ||
| Total equity | 697.4 | 684.3 | 690.7 | 662.7 | 628.5 | 582.9 | 587.1 | 344.1 | 399.3 | |
| TOTAL | 2,134.2 | 1,949.0 | 1,954.5 | 1,939.4 | 1,896.9 | 1,805.2 | 1,849.9 | 1,846.5 | ||
| As Previously Reported | Nonrelated Party | ||||||||||
| LIABILITIES: | ||||||||||
| Current maturities of long-term debt | 70.9 | 38.3 | ||||||||
| Long-term debt | 447.3 | 430.9 | ||||||||
| As Previously Reported | Related Party | ||||||||||
| ASSETS | ||||||||||
| Due from affiliates | 25.1 | 20.2 | ||||||||
| LIABILITIES: | ||||||||||
| Current maturities of long-term debt | 10.0 | |||||||||
| Long-term debt | 10.0 | |||||||||
| Restatement Impacts | ||||||||||
| ASSETS | ||||||||||
| Cash and cash equivalents | 0.0 | 0.0 | ||||||||
| Restricted cash | 0.0 | 0.0 | ||||||||
| Accounts receivable - net | 0.0 | 0.0 | ||||||||
| Non-trade receivables | 19.8 | 17.1 | 7.7 | 8.1 | (2.9) | (6.6) | 1.6 | 0.0 | ||
| Manufacturing credit receivable | 0.0 | 0.0 | ||||||||
| Inventories | 0.0 | 0.0 | ||||||||
| Derivative assets | 0.0 | 0.0 | ||||||||
| Prepaid and other current assets | 0.0 | 0.0 | ||||||||
| Total current assets | 19.8 | 17.1 | 7.7 | 8.1 | (2.9) | (6.6) | 1.6 | 0.0 | ||
| Property, plant and equipment - net | 167.0 | 175.2 | 169.8 | 171.5 | 164.4 | 158.0 | 153.7 | 180.0 | ||
| Manufacturing credit receivable - less current portion | 0.0 | 0.0 | ||||||||
| Other assets | 0.9 | 1.0 | 0.9 | 1.0 | 1.0 | 1.0 | 1.1 | 2.3 | ||
| TOTAL | 187.7 | 193.3 | 178.4 | 180.6 | 162.5 | 152.4 | 156.4 | 182.3 | ||
| LIABILITIES: | ||||||||||
| Accounts payable, trade | 0.0 | 0.0 | ||||||||
| Accrued compensation and benefits | 1.0 | 1.0 | 1.0 | 1.0 | 11.1 | 11.1 | 11.2 | 0.6 | ||
| Due to affiliates | 0.0 | 0.0 | ||||||||
| Accrued and other current liabilities | 3.2 | 3.1 | 2.6 | 2.6 | 0.0 | |||||
| Derivative liabilities | 0.0 | 0.0 | ||||||||
| Deferred credit - preliminary bargain purchase gain | 0.0 | |||||||||
| Total current liabilities | (7.6) | (3.6) | (3.8) | 3.6 | 0.6 | |||||
| Accrued benefits costs - less current portion | 14.5 | 14.5 | 14.5 | 14.5 | 15.4 | 12.2 | 12.8 | 9.1 | ||
| Other liabilities | 0.0 | 0.0 | ||||||||
| Deferred Income Tax Liabilities, Net | 0.0 | 0.0 | ||||||||
| Asset retirement obligations - less current portion | 19.4 | 19.3 | 20.7 | 19.8 | 13.5 | |||||
| Total noncurrent liabilities | 33.9 | 33.8 | 35.2 | 34.3 | 26.5 | 23.3 | 24.0 | 22.6 | ||
| Commitments and Contingencies | ||||||||||
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Preferred stock | 0.0 | 0.0 | ||||||||
| Common stock | 0.0 | 0.0 | ||||||||
| Additional paid-in capital | 0.0 | 0.0 | ||||||||
| Treasury stock, at cost | 0.0 | 0.0 | ||||||||
| Accumulated other comprehensive loss | 0.0 | 0.0 | ||||||||
| Accumulated deficit | 0.0 | 0.0 | ||||||||
| Total Century shareholders’ equity | 0.0 | 0.0 | ||||||||
| Noncontrolling interest | 161.4 | 163.1 | 147.1 | 142.7 | 136.0 | 129.1 | 132.4 | 159.1 | ||
| Total equity | 161.4 | 163.1 | 147.1 | 142.7 | 136.0 | 129.1 | 132.4 | 159.1 | $ 0.0 | |
| TOTAL | $ 187.7 | $ 193.3 | $ 178.4 | 180.6 | $ 162.5 | $ 152.4 | $ 156.4 | 182.3 | ||
| Restatement Impacts | Nonrelated Party | ||||||||||
| LIABILITIES: | ||||||||||
| Current maturities of long-term debt | 0.0 | 0.0 | ||||||||
| Long-term debt | 0.0 | 0.0 | ||||||||
| Restatement Impacts | Related Party | ||||||||||
| ASSETS | ||||||||||
| Due from affiliates | 0.0 | 0.0 | ||||||||
| LIABILITIES: | ||||||||||
| Current maturities of long-term debt | $ 0.0 | |||||||||
| Long-term debt | $ 0.0 |
Restatement of Previously Issued Financial Statements - Consolidated Statements of Cash Flows (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| CASH FLOWS FROM OPERATING ACTIVITIES: | |||||||||
| Net income (loss) | $ 8.2 | $ (11.7) | $ 22.4 | $ 37.4 | $ (11.6) | $ 241.2 | $ 15.8 | $ 306.7 | $ (56.6) |
| Adjustments to reconcile Net income (loss) to net cash provided by (used in) operating activities: | |||||||||
| Unrealized loss (gain) on derivative instruments | 62.8 | (5.0) | 87.1 | ||||||
| Depreciation, depletion and amortization | 91.8 | 86.7 | 79.0 | ||||||
| Change in deferred tax provision | (13.7) | (1.3) | (30.8) | ||||||
| Gain on sale of assets | (2.3) | ||||||||
| Bargain purchase gain | 0.0 | (245.9) | 0.0 | ||||||
| Force majeure settlement | 0.0 | (12.3) | 0.0 | ||||||
| Lower of cost or NRV inventory adjustment | 8.6 | 2.3 | 0.0 | ||||||
| Other non-cash items - net | 7.4 | (4.1) | (16.7) | ||||||
| Change in operating assets and liabilities, net of acquisition: | |||||||||
| Accounts receivable - net | (24.0) | (18.3) | 36.9 | ||||||
| Non-trade receivables | (2.1) | 23.3 | 4.1 | ||||||
| Manufacturing credit receivable | (20.7) | (92.6) | (59.3) | ||||||
| Due from affiliates | (4.5) | (4.9) | (15.5) | ||||||
| Inventories | 10.8 | (64.3) | 25.8 | ||||||
| Prepaid and other current assets | 3.8 | 1.0 | 2.9 | ||||||
| Accounts payable, trade | 1.4 | (50.6) | (19.4) | ||||||
| Due to affiliates | (13.2) | 26.1 | 51.7 | ||||||
| Accrued and other current liabilities | 11.6 | 4.0 | 0.0 | ||||||
| Ravenswood retiree medical settlement | (2.0) | (2.0) | (2.0) | ||||||
| PBGC settlement | (2.4) | (0.3) | (4.5) | ||||||
| Other - net | (13.2) | (1.9) | 2.8 | ||||||
| Net cash provided by (used in) operating activities | 185.0 | (24.6) | 105.6 | ||||||
| CASH FLOWS FROM INVESTING ACTIVITIES: | |||||||||
| Purchase of property, plant and equipment | (100.2) | (82.3) | (95.0) | ||||||
| Proceeds from co-tenancy assets at Jamalco JV | 0.0 | ||||||||
| Proceeds from sale of property, plant and equipment | 0.0 | 2.3 | 25.7 | ||||||
| Acquisition of subsidiary net of cash acquired | 0.0 | 0.0 | 11.5 | ||||||
| Net cash used in investing activities | (100.2) | (80.0) | (57.8) | ||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Contributions from joint venture partner | 19.9 | 12.7 | 0.0 | ||||||
| Carbon credit repayments | (28.3) | (10.0) | 0.0 | ||||||
| Carbon credit proceeds | 28.1 | 0.0 | 36.8 | ||||||
| Net cash provided by (used in) financing activities | 15.1 | 50.0 | (13.0) | ||||||
| CHANGE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH | 99.9 | (54.6) | 34.8 | ||||||
| Cash, cash equivalents and restricted cash, beginning of year | 35.7 | 90.3 | 35.7 | 90.3 | 55.5 | ||||
| Cash, cash equivalents and restricted cash, end of year | 135.6 | 35.7 | 90.3 | ||||||
| Cash paid for: | |||||||||
| Interest | 36.6 | 36.0 | 35.2 | ||||||
| Income taxes, net of refunds | 4.8 | 14.5 | 5.9 | ||||||
| Non-cash investing activities: | |||||||||
| Capital expenditures | 19.5 | 12.3 | 10.7 | ||||||
| Capitalized interest | 0.0 | 3.4 | 6.0 | ||||||
| Distribution of fixed assets to NCI | 0.0 | ||||||||
| Unadjusted Difference | |||||||||
| Adjustments to reconcile Net income (loss) to net cash provided by (used in) operating activities: | |||||||||
| Other non-cash items - net | 27.0 | 3.4 | |||||||
| U.S. and Iceland Revolving Credit Facilities | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under revolving credit facilities | 883.2 | 735.4 | 656.9 | ||||||
| Repayments under revolving credit facilities | (876.1) | (705.1) | (758.2) | ||||||
| Casthouse Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under facility agreements | 0.0 | 25.0 | 55.0 | ||||||
| Repayments under facility agreements | (123.2) | (6.8) | 0.0 | ||||||
| Iceland Term Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Repayments under revolving credit facilities | 0.0 | (1.2) | (13.5) | ||||||
| Vlissingen Facility Agreement | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Repayments under revolving credit facilities | (10.0) | 0.0 | 0.0 | ||||||
| Borrowings under facility agreements | 0.0 | 0.0 | 10.0 | ||||||
| As Previously Reported | |||||||||
| CASH FLOWS FROM OPERATING ACTIVITIES: | |||||||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | |
| Adjustments to reconcile Net income (loss) to net cash provided by (used in) operating activities: | |||||||||
| Unrealized loss (gain) on derivative instruments | (5.0) | 87.1 | |||||||
| Depreciation, depletion and amortization | 81.8 | 74.7 | |||||||
| Change in deferred tax provision | (1.3) | (30.8) | |||||||
| Gain on sale of assets | (2.3) | ||||||||
| Bargain purchase gain | (245.9) | 0.0 | |||||||
| Force majeure settlement | (12.3) | ||||||||
| Lower of cost or NRV inventory adjustment | 2.3 | ||||||||
| Other non-cash items - net | 9.1 | 3.4 | |||||||
| Change in operating assets and liabilities, net of acquisition: | |||||||||
| Accounts receivable - net | (18.3) | 36.9 | |||||||
| Non-trade receivables | 31.5 | 4.1 | |||||||
| Manufacturing credit receivable | (92.6) | (59.3) | |||||||
| Due from affiliates | (4.9) | (15.5) | |||||||
| Inventories | (64.3) | 25.8 | |||||||
| Prepaid and other current assets | 1.0 | 2.9 | |||||||
| Accounts payable, trade | (50.6) | (19.4) | |||||||
| Due to affiliates | 26.1 | 51.7 | |||||||
| Accrued and other current liabilities | (1.2) | ||||||||
| Ravenswood retiree medical settlement | (2.0) | (2.0) | |||||||
| PBGC settlement | (0.3) | (4.5) | |||||||
| Other - net | 3.9 | 2.8 | |||||||
| Net cash provided by (used in) operating activities | (24.6) | 105.6 | |||||||
| CASH FLOWS FROM INVESTING ACTIVITIES: | |||||||||
| Purchase of property, plant and equipment | (82.3) | (95.0) | |||||||
| Proceeds from co-tenancy assets at Jamalco JV | 12.7 | ||||||||
| Proceeds from sale of property, plant and equipment | 2.3 | 25.7 | |||||||
| Acquisition of subsidiary net of cash acquired | 11.5 | ||||||||
| Net cash used in investing activities | (67.3) | (57.8) | |||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Contributions from joint venture partner | 0.0 | ||||||||
| Carbon credit repayments | (10.0) | ||||||||
| Carbon credit proceeds | 36.8 | ||||||||
| Net cash provided by (used in) financing activities | 37.3 | (13.0) | |||||||
| CHANGE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH | (54.6) | 34.8 | |||||||
| Cash, cash equivalents and restricted cash, beginning of year | 35.7 | 90.3 | 35.7 | 90.3 | 55.5 | ||||
| Cash, cash equivalents and restricted cash, end of year | 35.7 | 90.3 | |||||||
| Cash paid for: | |||||||||
| Interest | 36.0 | ||||||||
| Income taxes, net of refunds | 14.5 | ||||||||
| Non-cash investing activities: | |||||||||
| Capital expenditures | 12.3 | ||||||||
| Capitalized interest | 3.4 | ||||||||
| Distribution of fixed assets to NCI | 17.0 | ||||||||
| As Previously Reported | U.S. and Iceland Revolving Credit Facilities | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under revolving credit facilities | 735.4 | 656.9 | |||||||
| Repayments under revolving credit facilities | (705.1) | (758.2) | |||||||
| As Previously Reported | Casthouse Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under facility agreements | 25.0 | 55.0 | |||||||
| Repayments under facility agreements | (6.8) | ||||||||
| As Previously Reported | Iceland Term Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Repayments under revolving credit facilities | (1.2) | (13.5) | |||||||
| As Previously Reported | Vlissingen Facility Agreement | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under facility agreements | 10.0 | ||||||||
| Restatement Impacts | |||||||||
| CASH FLOWS FROM OPERATING ACTIVITIES: | |||||||||
| Net income (loss) | $ (2.4) | $ (2.6) | (3.3) | $ (4.9) | $ (4.9) | (3.5) | (14.0) | (4.3) | |
| Adjustments to reconcile Net income (loss) to net cash provided by (used in) operating activities: | |||||||||
| Unrealized loss (gain) on derivative instruments | 0.0 | 0.0 | |||||||
| Depreciation, depletion and amortization | 4.9 | 4.3 | |||||||
| Change in deferred tax provision | 0.0 | 0.0 | |||||||
| Gain on sale of assets | 0.0 | ||||||||
| Bargain purchase gain | 0.0 | 0.0 | |||||||
| Force majeure settlement | 0.0 | ||||||||
| Lower of cost or NRV inventory adjustment | 0.0 | ||||||||
| Other non-cash items - net | 17.9 | 0.0 | |||||||
| Change in operating assets and liabilities, net of acquisition: | |||||||||
| Accounts receivable - net | 0.0 | 0.0 | |||||||
| Non-trade receivables | (8.2) | 0.0 | |||||||
| Manufacturing credit receivable | 0.0 | 0.0 | |||||||
| Due from affiliates | 0.0 | 0.0 | |||||||
| Inventories | 0.0 | 0.0 | |||||||
| Prepaid and other current assets | 0.0 | 0.0 | |||||||
| Accounts payable, trade | 0.0 | 0.0 | |||||||
| Due to affiliates | 0.0 | 0.0 | |||||||
| Accrued and other current liabilities | 5.2 | ||||||||
| Ravenswood retiree medical settlement | 0.0 | 0.0 | |||||||
| PBGC settlement | 0.0 | 0.0 | |||||||
| Other - net | (5.8) | 0.0 | |||||||
| Net cash provided by (used in) operating activities | 0.0 | 0.0 | |||||||
| CASH FLOWS FROM INVESTING ACTIVITIES: | |||||||||
| Purchase of property, plant and equipment | 0.0 | 0.0 | |||||||
| Proceeds from co-tenancy assets at Jamalco JV | (12.7) | ||||||||
| Proceeds from sale of property, plant and equipment | 0.0 | 0.0 | |||||||
| Acquisition of subsidiary net of cash acquired | 0.0 | ||||||||
| Net cash used in investing activities | (12.7) | 0.0 | |||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Contributions from joint venture partner | 12.7 | ||||||||
| Carbon credit repayments | 0.0 | ||||||||
| Carbon credit proceeds | 0.0 | ||||||||
| Net cash provided by (used in) financing activities | 12.7 | 0.0 | |||||||
| CHANGE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH | 0.0 | 0.0 | |||||||
| Cash, cash equivalents and restricted cash, beginning of year | $ 0.0 | $ 0.0 | $ 0.0 | 0.0 | 0.0 | ||||
| Cash, cash equivalents and restricted cash, end of year | 0.0 | 0.0 | |||||||
| Cash paid for: | |||||||||
| Interest | 0.0 | ||||||||
| Income taxes, net of refunds | 0.0 | ||||||||
| Non-cash investing activities: | |||||||||
| Capital expenditures | 0.0 | ||||||||
| Capitalized interest | 0.0 | ||||||||
| Distribution of fixed assets to NCI | (17.0) | ||||||||
| Restatement Impacts | U.S. and Iceland Revolving Credit Facilities | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under revolving credit facilities | 0.0 | 0.0 | |||||||
| Repayments under revolving credit facilities | 0.0 | 0.0 | |||||||
| Restatement Impacts | Casthouse Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under facility agreements | 0.0 | 0.0 | |||||||
| Repayments under facility agreements | 0.0 | ||||||||
| Restatement Impacts | Iceland Term Facility | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Repayments under revolving credit facilities | $ 0.0 | 0.0 | |||||||
| Restatement Impacts | Vlissingen Facility Agreement | |||||||||
| CASH FLOWS FROM FINANCING ACTIVITIES: | |||||||||
| Borrowings under facility agreements | $ 0.0 | ||||||||
Restatement of Previously Issued Financial Statements - Consolidated Statements of Stockholders' Equity (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | $ 847.4 | $ 837.8 | $ 805.4 | $ 712.0 | $ 719.5 | $ 503.2 | $ 805.4 | $ 503.2 | $ 399.3 | ||||
| Net income (loss) | 8.2 | (11.7) | 22.4 | 37.4 | (11.6) | 241.2 | 15.8 | 306.7 | (56.6) | ||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (24.0) | 39.3 | (5.3) | [1] | 170.2 | [1] | ||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | 48.1 | (6.6) | (13.0) | ||||
| Share-based compensation | 1.0 | 1.2 | 0.6 | 1.6 | 1.0 | 0.8 | 21.3 | 7.3 | 3.3 | ||||
| Ending balance | 858.8 | 847.4 | 837.8 | 764.5 | 712.0 | 719.5 | 929.9 | 805.4 | 503.2 | ||||
| Unadjusted Difference | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 805.3 | 805.3 | |||||||||||
| Ending balance | 929.9 | 805.3 | |||||||||||
| Noncontrolling interest | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 123.0 | 111.5 | 111.0 | 110.5 | 118.0 | 147.6 | 111.0 | 147.6 | 0.0 | ||||
| Net income (loss) | (6.7) | (7.1) | (7.3) | (9.9) | (9.1) | (5.6) | (26.0) | (30.1) | (13.5) | ||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (24.0) | 39.3 | (5.3) | [1] | 170.2 | [1] | ||
| Other comprehensive income (loss) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (1.2) | (9.1) | |||||
| Share-based compensation | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||||
| Ending balance | 117.0 | 123.0 | 111.5 | 112.4 | 110.5 | 118.0 | 124.3 | 111.0 | 147.6 | ||||
| As Previously Reported | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 684.3 | 690.7 | 662.7 | 582.9 | 587.1 | 344.1 | 662.7 | 344.1 | 399.3 | ||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | |||||
| Noncontrolling interest increase (decrease) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (0.8) | (4.0) | (2.3) | |||||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | (5.4) | (3.9) | |||||
| Share-based compensation | 1.0 | 1.2 | 0.6 | 1.6 | 1.0 | 0.8 | 7.3 | 3.3 | |||||
| Ending balance | 697.4 | 684.3 | 690.7 | 628.5 | 582.9 | 587.1 | 662.7 | 344.1 | |||||
| As Previously Reported | Noncontrolling interest | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | (40.1) | (35.6) | (31.6) | (18.6) | (14.4) | (11.5) | (31.6) | (11.5) | 0.0 | ||||
| Net income (loss) | (4.3) | (4.5) | (4.0) | (5.0) | (4.2) | (2.1) | (16.1) | (9.2) | |||||
| Noncontrolling interest increase (decrease) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (0.8) | (4.0) | (2.3) | |||||
| Other comprehensive income (loss) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||
| Share-based compensation | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||||
| Ending balance | (44.4) | (40.1) | (35.6) | (23.6) | (18.6) | (14.4) | (31.6) | (11.5) | |||||
| Restatement Impacts | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 163.1 | 147.1 | 142.7 | 129.1 | 132.4 | 159.1 | 142.7 | 159.1 | 0.0 | ||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | |||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (23.2) | (1.3) | 172.5 | |||||
| Other comprehensive income (loss) | (1.2) | (9.1) | |||||||||||
| Share-based compensation | 0.0 | 0.0 | |||||||||||
| Ending balance | 161.4 | 163.1 | 147.1 | 136.0 | 129.1 | 132.4 | 142.7 | 159.1 | |||||
| Restatement Impacts | Unadjusted Difference | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 142.6 | 142.6 | |||||||||||
| Ending balance | 142.6 | ||||||||||||
| Restatement Impacts | Noncontrolling interest | |||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | |||||||||||||
| Beginning balance | 142.6 | 159.1 | $ 142.6 | 159.1 | 0.0 | ||||||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | |||||
| Noncontrolling interest increase (decrease) | $ 0.7 | $ 18.6 | $ 7.8 | $ 11.8 | $ 1.6 | $ (23.2) | (1.3) | 172.5 | |||||
| Other comprehensive income (loss) | (1.2) | (9.1) | |||||||||||
| Ending balance | $ 142.6 | $ 159.1 | |||||||||||
| |||||||||||||
Quarterly Financial Information (Unaudited and Restated) - Statement of Operations (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | ||||||||||||||
| Cost of Goods Sold | $ 557.3 | $ 594.5 | $ 576.6 | $ 462.2 | $ 545.3 | $ 476.5 | $ 2,271.5 | [1] | $ 2,048.3 | [1] | $ 2,097.8 | [1] | ||
| Gross profit | 74.9 | 33.6 | 57.3 | 76.9 | 15.5 | 13.0 | 256.4 | 172.0 | 87.6 | |||||
| Operating income (loss) | 55.9 | 18.1 | 42.8 | 58.9 | 1.5 | (1.6) | 158.1 | 108.4 | 27.5 | |||||
| Income before income taxes | 7.1 | (13.0) | 24.0 | 39.4 | (11.1) | 241.7 | 2.7 | 309.8 | (71.1) | |||||
| Net income (loss) | 8.2 | (11.7) | 22.4 | 37.4 | (11.6) | 241.2 | 15.8 | 306.7 | (56.6) | |||||
| Net loss attributable to noncontrolling interests | (6.7) | (7.1) | (7.3) | (9.9) | (9.1) | (5.6) | (26.0) | (30.1) | (13.5) | |||||
| Net income (loss) attributable to Century stockholders | 14.9 | (4.6) | 29.7 | 47.3 | (2.5) | 246.8 | 41.8 | 336.8 | (43.1) | |||||
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 1.8 | 17.9 | 0.0 | |||||
| Net income (loss) allocated to common stockholders | 14.1 | (4.6) | 28.2 | 44.8 | (2.5) | 233.6 | $ 40.0 | 318.9 | (43.1) | |||||
| As Previously Reported | ||||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | ||||||||||||||
| Cost of Goods Sold | 554.9 | 591.9 | 573.3 | 457.3 | 540.4 | 473.0 | 2,035.3 | 2,093.5 | ||||||
| Gross profit | 77.3 | 36.2 | 60.6 | 81.8 | 20.4 | 16.5 | 185.0 | 91.9 | ||||||
| Operating income (loss) | 58.3 | 20.7 | 46.1 | 63.8 | 6.4 | 1.9 | 121.4 | 31.8 | ||||||
| Income before income taxes | 9.5 | (10.4) | 27.3 | 44.3 | (6.2) | 245.2 | 323.8 | (66.8) | ||||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | ||||||
| Net loss attributable to noncontrolling interests | (4.3) | (4.5) | (4.0) | (5.0) | (4.2) | (2.1) | (16.1) | (9.2) | ||||||
| Net income (loss) attributable to Century stockholders | 14.9 | (4.6) | 29.7 | 47.3 | (2.5) | 246.8 | 336.8 | (43.1) | ||||||
| Less: Net income allocated to participating securities | 0.8 | 0.0 | 1.5 | 2.5 | 0.0 | 13.2 | 17.9 | 0.0 | ||||||
| Net income (loss) allocated to common stockholders | 14.1 | (4.6) | 28.2 | 44.8 | (2.5) | 233.6 | 318.9 | (43.1) | ||||||
| Restatement Impacts | ||||||||||||||
| Error Corrections and Prior Period Adjustments Restatement [Line Items] | ||||||||||||||
| Cost of Goods Sold | 2.4 | 2.6 | 3.3 | 4.9 | 4.9 | 3.5 | 13.0 | 4.3 | ||||||
| Gross profit | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (13.0) | (4.3) | ||||||
| Operating income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (13.0) | (4.3) | ||||||
| Income before income taxes | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Net loss attributable to noncontrolling interests | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | ||||||
| Net income (loss) attributable to Century stockholders | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | ||||||
| Less: Net income allocated to participating securities | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | ||||||
| Net income (loss) allocated to common stockholders | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | ||||||
| ||||||||||||||
Quarterly Financial Information (Unaudited and Restated) - Consolidated Balance Statements (Details) - USD ($) $ in Millions |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
|---|---|---|---|---|---|---|---|---|---|---|
| ASSETS | ||||||||||
| Non-trade receivables | $ 38.1 | $ 19.8 | $ 17.1 | $ 7.7 | $ 21.3 | $ 49.8 | $ 46.9 | $ 40.1 | $ 36.2 | |
| Total current assets | 1,031.3 | 1,046.9 | 807.4 | 829.6 | 810.9 | 804.0 | 729.3 | 782.7 | 767.1 | |
| Property, plant and equipment - net | 1,167.6 | 1,139.2 | 1,150.8 | 1,142.0 | 1,149.8 | 1,129.7 | 1,129.5 | 1,137.9 | 1,184.2 | |
| Other assets | 70.4 | 72.0 | 70.6 | 70.2 | 88.9 | 125.7 | 98.8 | 85.7 | 77.5 | |
| TOTAL | 2,269.3 | 2,321.9 | 2,142.3 | 2,132.8 | 2,120.0 | 2,059.4 | 1,957.6 | 2,006.3 | 2,028.8 | |
| LIABILITIES | ||||||||||
| Accrued compensation and benefits | 74.4 | 53.4 | 45.2 | 41.6 | 50.8 | 130.3 | 131.3 | 132.5 | 38.7 | |
| Non-trade payables | 0.0 | 0.0 | 0.0 | |||||||
| Accrued and other current liabilities | 35.6 | 76.8 | 48.0 | 39.2 | 44.6 | 50.9 | ||||
| Total current liabilities | 523.6 | 591.5 | 447.5 | 443.6 | 467.3 | 763.6 | ||||
| Accrued benefits costs - less current portion | 97.7 | 136.3 | 142.3 | 143.8 | 144.9 | 69.5 | 62.1 | 63.2 | 129.4 | |
| Asset retirement obligations - less current portion | 75.3 | 83.3 | 82.5 | 85.1 | 81.3 | 63.0 | ||||
| Total noncurrent liabilities | 815.8 | 871.6 | 847.4 | 851.6 | 847.3 | 822.6 | 817.5 | 817.9 | 762.0 | |
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Noncontrolling interest | 124.3 | 117.0 | 123.0 | 111.5 | 111.0 | 112.4 | 110.5 | 118.0 | 147.6 | |
| Total equity | 929.9 | 858.8 | 847.4 | 837.8 | 805.4 | 764.5 | 712.0 | 719.5 | 503.2 | $ 399.3 |
| TOTAL | $ 2,269.3 | 2,321.9 | 2,142.3 | 2,132.8 | 2,120.0 | 2,059.4 | 1,957.6 | 2,006.3 | 2,028.8 | |
| As Previously Reported | ||||||||||
| ASSETS | ||||||||||
| Non-trade receivables | 0.0 | 0.0 | 0.0 | 13.2 | 52.7 | 53.5 | 38.5 | 36.2 | ||
| Total current assets | 1,027.1 | 790.3 | 821.9 | 802.8 | 806.9 | 735.9 | 781.1 | 767.1 | ||
| Property, plant and equipment - net | 972.2 | 975.6 | 972.2 | 978.3 | 965.3 | 971.5 | 984.2 | 1,004.2 | ||
| Other assets | 71.1 | 69.6 | 69.3 | 87.9 | 124.7 | 97.8 | 84.6 | 75.2 | ||
| TOTAL | 2,134.2 | 1,949.0 | 1,954.5 | 1,939.4 | 1,896.9 | 1,805.2 | 1,849.9 | 1,846.5 | ||
| LIABILITIES | ||||||||||
| Accrued compensation and benefits | 52.4 | 44.2 | 40.6 | 49.8 | 119.2 | 120.2 | 121.3 | 38.1 | ||
| Non-trade payables | 11.8 | 7.7 | 7.4 | |||||||
| Accrued and other current liabilities | 73.6 | 44.9 | 36.6 | 42.0 | 50.9 | |||||
| Total current liabilities | 599.1 | 451.1 | 447.4 | 463.7 | 763.0 | |||||
| Accrued benefits costs - less current portion | 121.8 | 127.8 | 129.3 | 130.4 | 54.1 | 49.9 | 50.4 | 120.3 | ||
| Asset retirement obligations - less current portion | 63.9 | 63.2 | 64.4 | 61.5 | 49.5 | |||||
| Total noncurrent liabilities | 837.7 | 813.6 | 816.4 | 813.0 | 796.1 | 794.2 | 793.9 | 739.4 | ||
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Noncontrolling interest | (44.4) | (40.1) | (35.6) | (31.7) | (23.6) | (18.6) | (14.4) | (11.5) | ||
| Total equity | 697.4 | 684.3 | 690.7 | 662.7 | 628.5 | 582.9 | 587.1 | 344.1 | 399.3 | |
| TOTAL | 2,134.2 | 1,949.0 | 1,954.5 | 1,939.4 | 1,896.9 | 1,805.2 | 1,849.9 | 1,846.5 | ||
| Restatement Impacts | ||||||||||
| ASSETS | ||||||||||
| Non-trade receivables | 19.8 | 17.1 | 7.7 | 8.1 | (2.9) | (6.6) | 1.6 | 0.0 | ||
| Total current assets | 19.8 | 17.1 | 7.7 | 8.1 | (2.9) | (6.6) | 1.6 | 0.0 | ||
| Property, plant and equipment - net | 167.0 | 175.2 | 169.8 | 171.5 | 164.4 | 158.0 | 153.7 | 180.0 | ||
| Other assets | 0.9 | 1.0 | 0.9 | 1.0 | 1.0 | 1.0 | 1.1 | 2.3 | ||
| TOTAL | 187.7 | 193.3 | 178.4 | 180.6 | 162.5 | 152.4 | 156.4 | 182.3 | ||
| LIABILITIES | ||||||||||
| Accrued compensation and benefits | 1.0 | 1.0 | 1.0 | 1.0 | 11.1 | 11.1 | 11.2 | 0.6 | ||
| Non-trade payables | (11.8) | (7.7) | (7.4) | |||||||
| Accrued and other current liabilities | 3.2 | 3.1 | 2.6 | 2.6 | 0.0 | |||||
| Total current liabilities | (7.6) | (3.6) | (3.8) | 3.6 | 0.6 | |||||
| Accrued benefits costs - less current portion | 14.5 | 14.5 | 14.5 | 14.5 | 15.4 | 12.2 | 12.8 | 9.1 | ||
| Asset retirement obligations - less current portion | 19.4 | 19.3 | 20.7 | 19.8 | 13.5 | |||||
| Total noncurrent liabilities | 33.9 | 33.8 | 35.2 | 34.3 | 26.5 | 23.3 | 24.0 | 22.6 | ||
| SHAREHOLDERS’ EQUITY: | ||||||||||
| Noncontrolling interest | 161.4 | 163.1 | 147.1 | 142.7 | 136.0 | 129.1 | 132.4 | 159.1 | ||
| Total equity | 161.4 | 163.1 | 147.1 | 142.7 | 136.0 | 129.1 | 132.4 | 159.1 | $ 0.0 | |
| TOTAL | $ 187.7 | $ 193.3 | $ 178.4 | $ 180.6 | $ 162.5 | $ 152.4 | $ 156.4 | $ 182.3 |
Quarterly Financial Information (Unaudited and Restated) - Consolidated Statements of Shareholders' Equity (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2024 |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | $ 847.4 | $ 837.8 | $ 805.4 | $ 712.0 | $ 719.5 | $ 503.2 | $ 805.4 | $ 503.2 | $ 399.3 | ||||
| Net income (loss) | 8.2 | (11.7) | 22.4 | 37.4 | (11.6) | 241.2 | 15.8 | 306.7 | (56.6) | ||||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | 48.1 | (6.6) | (13.0) | ||||
| Share-based compensation | 1.0 | 1.2 | 0.6 | 1.6 | 1.0 | 0.8 | 21.3 | 7.3 | 3.3 | ||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (24.0) | 39.3 | (5.3) | [1] | 170.2 | [1] | ||
| Ending balance | 858.8 | 847.4 | 837.8 | 764.5 | 712.0 | 719.5 | 929.9 | 805.4 | 503.2 | ||||
| Unadjusted Difference | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 805.3 | 805.3 | |||||||||||
| Ending balance | 929.9 | 805.3 | |||||||||||
| As Previously Reported | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 684.3 | 690.7 | 662.7 | 582.9 | 587.1 | 344.1 | 662.7 | 344.1 | 399.3 | ||||
| Net income (loss) | 10.6 | (9.1) | 25.7 | 42.3 | (6.7) | 244.7 | 320.7 | (52.3) | |||||
| Other comprehensive income (loss) | 1.5 | 1.5 | 1.7 | 1.7 | 1.5 | (1.7) | (5.4) | (3.9) | |||||
| Share-based compensation | 1.0 | 1.2 | 0.6 | 1.6 | 1.0 | 0.8 | 7.3 | 3.3 | |||||
| Noncontrolling interest increase (decrease) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (0.8) | (4.0) | (2.3) | |||||
| Ending balance | 697.4 | 684.3 | 690.7 | 628.5 | 582.9 | 587.1 | 662.7 | 344.1 | |||||
| Restatement Impacts | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 163.1 | 147.1 | 142.7 | 129.1 | 132.4 | 159.1 | 142.7 | 159.1 | 0.0 | ||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | |||||
| Other comprehensive income (loss) | (1.2) | (9.1) | |||||||||||
| Share-based compensation | 0.0 | 0.0 | |||||||||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (23.2) | (1.3) | 172.5 | |||||
| Ending balance | 161.4 | 163.1 | 147.1 | 136.0 | 129.1 | 132.4 | 142.7 | 159.1 | |||||
| Restatement Impacts | Unadjusted Difference | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 142.6 | 142.6 | |||||||||||
| Ending balance | 142.6 | ||||||||||||
| Noncontrolling interest | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 123.0 | 111.5 | 111.0 | 110.5 | 118.0 | 147.6 | 111.0 | 147.6 | 0.0 | ||||
| Net income (loss) | (6.7) | (7.1) | (7.3) | (9.9) | (9.1) | (5.6) | (26.0) | (30.1) | (13.5) | ||||
| Other comprehensive income (loss) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (1.2) | (9.1) | |||||
| Share-based compensation | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||||
| Noncontrolling interest increase (decrease) | 0.7 | 18.6 | 7.8 | 11.8 | 1.6 | (24.0) | 39.3 | (5.3) | [1] | 170.2 | [1] | ||
| Ending balance | 117.0 | 123.0 | 111.5 | 112.4 | 110.5 | 118.0 | 124.3 | 111.0 | 147.6 | ||||
| Noncontrolling interest | As Previously Reported | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | (40.1) | (35.6) | (31.6) | (18.6) | (14.4) | (11.5) | (31.6) | (11.5) | 0.0 | ||||
| Net income (loss) | (4.3) | (4.5) | (4.0) | (5.0) | (4.2) | (2.1) | (16.1) | (9.2) | |||||
| Other comprehensive income (loss) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||
| Share-based compensation | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||||||
| Noncontrolling interest increase (decrease) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | (0.8) | (4.0) | (2.3) | |||||
| Ending balance | (44.4) | (40.1) | (35.6) | (23.6) | (18.6) | (14.4) | (31.6) | (11.5) | |||||
| Noncontrolling interest | Restatement Impacts | |||||||||||||
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | |||||||||||||
| Beginning balance | 142.6 | 159.1 | $ 142.6 | 159.1 | 0.0 | ||||||||
| Net income (loss) | (2.4) | (2.6) | (3.3) | (4.9) | (4.9) | (3.5) | (14.0) | (4.3) | |||||
| Other comprehensive income (loss) | (1.2) | (9.1) | |||||||||||
| Noncontrolling interest increase (decrease) | $ 0.7 | $ 18.6 | $ 7.8 | $ 11.8 | $ 1.6 | $ (23.2) | (1.3) | 172.5 | |||||
| Ending balance | $ 142.6 | $ 159.1 | |||||||||||
| |||||||||||||
Subsequent Events (Details) - Subsequent Event t in Thousands, $ in Millions |
Feb. 02, 2026
USD ($)
|
Jan. 26, 2026
t
|
|---|---|---|
| Letter of Credit | Revolving Credit Facility | ||
| Subsequent Event [Line Items] | ||
| Letter of credit terminated | $ 8.1 | |
| Hawesville | Discontinued Operations, Disposed of by Sale | ||
| Subsequent Event [Line Items] | ||
| Proceeds from sale of hawesville facility | $ 200.0 | |
| Primary Aluminum Smelter | ||
| Subsequent Event [Line Items] | ||
| Ownership percentage by noncontrolling owners | 40.00% | |
| Number of expected production tonnes | t | 750 | |
| Terawulf Affiliate | Hawesville | Discontinued Operations, Disposed of by Sale | ||
| Subsequent Event [Line Items] | ||
| Non-dilutive minority equity interest, percent | 6.80% | |
| Emirates Global Aluminum | Primary Aluminum Smelter | ||
| Subsequent Event [Line Items] | ||
| Parent ownership percentage | 60.00% |