Century Aluminum (CENX) 10-Q 8 Aug 24 2024 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Jun. 30, 2024	Aug. 07, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2024
Document Transition Report	false
Entity File Number	001-34474
Entity Registrant Name	Century Aluminum Company
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3070826
Entity Address, Address Line One	One South Wacker Drive
Entity Address, Address Line Two	Suite 1000
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	312
Local Phone Number	696-3101
Title of 12(b) Security	Common Stock, $0.01 par value per share
Entity Trading Symbol	CENX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		92,785,652
Entity Central Index Key	0000949157
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
NET SALES:
Total net sales	$ 560.8	$ 575.5	$ 1,050.3	$ 1,127.9
Cost of goods sold	540.4	559.6	1,013.4	1,063.9
Gross profit	20.4	15.9	36.9	64
Selling, general and administrative expenses	12.3	12	26.4	25.4
Other operating expense - net	1.7	4.6	2.2	11.8
Operating income (loss)	6.4	(0.7)	8.3	26.8
Interest expense	(10.3)	(8.7)	(19.5)	(17.4)
Interest income	0.6	0.4	1.3	0.7
Net gain (loss) on forward and derivative contracts	(4)	9.1	3.4	(48.5)
Bargain purchase gain	0	0	245.9	0
Other income (loss) - net	1.1	(3.5)	(0.4)	(3.8)
Income (loss) before income taxes	(6.2)	(3.4)	239	(42.2)
Income tax (expense) benefit	(0.5)	10	(1)	10.2
Net income (loss)	(6.7)	6.6	238	(32)
Net loss attributable to noncontrolling interests	(4.2)	(0.9)	(6.3)	(0.9)
Net income (loss) attributable to Century stockholders	(2.5)	7.5	244.3	(31.1)
Less: net income allocated to participating securities	0	0.4	13	0
Net income (loss) allocated to common stockholders	$ (2.5)	$ 7.1	$ 231.3	$ (31.1)
NET INCOME (LOSS) ATTRIBUTABLE TO CENTURY STOCKHOLDERS PER COMMON SHARE:
Basic (in dollars per share)	$ (0.03)	$ 0.08	$ 2.50	$ (0.34)
Diluted (in dollars per share)	$ (0.03)	$ 0.07	$ 2.24	$ (0.34)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	92.7	92.3	92.7	92.3
Diluted (in shares)	92.7	93.2	98.8	92.3
Related Party
NET SALES:
Total net sales	$ 324.2	$ 427.2	$ 639.2	$ 839.4
Nonrelated Party
NET SALES:
Total net sales	$ 236.6	$ 148.3	$ 411.1	$ 288.5

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Comprehensive income (loss):
Net income (loss)	$ (6.7)	$ 6.6	$ 238	$ (32)
Other comprehensive income (loss) before income tax effect:
Net gain loss on foreign currency cash flow hedges reclassified as income	0	0	(0.1)	(0.1)
Defined benefit plans and other postretirement benefits:
Net loss arising during the period	0	0	(3.4)	0
Amortization of prior service benefit (cost) during the period	(0.1)	0.1	0	0.1
Amortization of net gain during the period	1.6	2.1	3.3	3.3
Other comprehensive (loss) income before income tax effect	1.5	2.2	(0.2)	3.3
Income tax effect	0	0	0	0
Other comprehensive income (loss)	1.5	2.2	(0.2)	3.3
Comprehensive income (loss)	(5.2)	8.8	237.8	(28.7)
Comprehensive loss attributable to noncontrolling interests	(4.2)	(0.9)	(6.3)	(0.9)
Comprehensive income (loss) attributable to Century stockholders	$ (1)	$ 9.7	$ 244.1	$ (27.8)

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
ASSETS
Cash and cash equivalents	$ 41.3	$ 88.8
Restricted cash	1.5	1.5
Accounts receivable - net	83.7	53.7
Non-trade receivables	53.5	36.2
Manufacturing credit receivable	57.1	59.3
Inventories	467.5	477
Derivative assets	5.4	2.9
Prepaid and other current assets	18.4	27.5
Total current assets	735.9	767.1
Property, plant and equipment - net	971.5	1,004.2
Other assets	97.8	75.2
TOTAL ASSETS	1,805.2	1,846.5
LIABILITIES:
Accounts payable, trade	200.3	249.5
Accrued compensation and benefits	38.2	38.1
Accrued and other current liabilities	49.5	50.9
Derivative liabilities	2.7	1.4
Deferred credit - preliminary bargain purchase gain	0	273.4
Total current liabilities	428.1	763
Accrued benefits costs - less current portion	120.2	120.3
Deferred taxes	73.4	72.4
Asset retirement obligations - less current portion	49.9	49.5
Other liabilities	99.4	66.3
Total noncurrent liabilities	794.2	739.4
TOTAL LIABILITIES	1,222.3	1,502.4
COMMITMENTS AND CONTINGENCIES (NOTE 12)
SHAREHOLDERS’ EQUITY:
Preferred stock (Note 8)	0	0
Common stock (Note 8)	1	1
Additional paid-in capital	2,544.7	2,542.9
Treasury stock, at cost	(86.3)	(86.3)
Accumulated other comprehensive loss	(98.1)	(97.9)
Accumulated deficit	(1,759.8)	(2,004.1)
Total Century shareholders’ equity	601.5	355.6
Noncontrolling interests	(18.6)	(11.5)
Total equity	582.9	344.1
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,805.2	1,846.5
Related Party
ASSETS
Due from affiliates	7.5	20.2
LIABILITIES:
Due to affiliates	108.3	101.4
Current maturities of long-term debt	10	10
Nonrelated Party
LIABILITIES:
Current maturities of long-term debt	19.1	38.3
Long-term debt	$ 451.3	$ 430.9

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ (6.7)	$ 6.6	$ 238	$ (32)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Unrealized (gain) loss on derivative instruments			(3.7)	66.3
Depreciation, depletion and amortization			41.7	31.5
Change in deferred tax benefit (expense)			0.6	(12.6)
Gain on sale of assets			(2.3)	0
Bargain purchase gain	0	0	(245.9)	0
Other non-cash items - net			0.5	3.7
Change in operating assets and liabilities, net of acquisition:
Accounts receivable - net			(37.4)	26
Non-trade receivables			(1.6)	0
Manufacturing credit receivable			(23.8)	0
Due from affiliates			12.8	(12.2)
Inventories			9.4	(18.5)
Prepaid and other current assets			10	7.7
Accounts payable, trade			(13.4)	(72.9)
Due to affiliates			8.8	7.7
Accrued and other current liabilities			(0.5)	3
Other - net			3.5	0.4
Net cash used in operating activities			(3.3)	(1.9)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property, plant and equipment			(46.6)	(36.6)
Proceeds from sale of assets			2.3	0
Acquisition of subsidiary, net of cash acquired			0	19.4
Net cash used in investing activities			(44.3)	(17.2)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net cash provided by financing activities			0.1	25.1
CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH			(47.5)	6
Cash, cash equivalents and restricted cash, beginning of period			90.3	55.5	$ 55.5
Cash, cash equivalents and restricted cash, end of period	$ 42.8	$ 61.5	42.8	61.5	$ 90.3
Cash paid for:
Interest			16.6	17.9
Taxes, net of refunds			3.8	(0.3)
Non-cash investing activities:
Capital expenditures			5.9	7.8
Capitalized interest			3.4	2.3
Distribution of property, plant and equipment to NCI			8.3	0
U.S. and Iceland Revolving Credit Facilities
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under revolving credit facilities			297.9	407.8
Repayments under facilities			(321.6)	(396.6)
Iceland Term Facility
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments under facilities			(1.2)	(6.1)
Casthouse Facility
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under Grundartangi casthouse debt facility			$ 25	$ 20

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Total Century Equity	Preferred stock	Common stock	Additional paid-in capital	Treasury stock, at cost	Accumulated other comprehensive loss	Accumulated deficit	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2022			53,854
Beginning balance at Dec. 31, 2022	$ 399.3	$ 399.3	$ 0	$ 1	$ 2,539.6	$ (86.3)	$ (94)	$ (1,961)	$ 0
Beginning balance (in shares) at Dec. 31, 2022				92,323,978
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(32)	(31.1)						(31.1)	(0.9)
Other comprehensive (loss) income	3.3	3.3					3.3
Share-based compensation (in shares)				19,735
Share-based compensation	1.4	1.4			1.4
Conversion of preferred stock to common stock (in shares)			(148)	14,836
Noncontrolling interest	32.8								32.8
Ending balance (in shares) at Jun. 30, 2023			53,706
Ending balance at Jun. 30, 2023	404.8	372.9	$ 0	$ 1	2,541	(86.3)	(90.7)	(1,992.1)	31.9
Ending balance (in shares) at Jun. 30, 2023				92,358,549
Beginning balance (in shares) at Mar. 31, 2023			53,854
Beginning balance at Mar. 31, 2023	362.4	362.4	$ 0	$ 1	2,540.2	(86.3)	(92.9)	(1,999.6)	0
Beginning balance (in shares) at Mar. 31, 2023				92,323,978
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	6.6	7.5						7.5	(0.9)
Other comprehensive (loss) income	2.2	2.2					2.2
Share-based compensation (in shares)				19,735
Share-based compensation	0.8	0.8			0.8
Conversion of preferred stock to common stock (in shares)			(148)	14,836
Noncontrolling interest	32.8								32.8
Ending balance (in shares) at Jun. 30, 2023			53,706
Ending balance at Jun. 30, 2023	404.8	372.9	$ 0	$ 1	2,541	(86.3)	(90.7)	(1,992.1)	31.9
Ending balance (in shares) at Jun. 30, 2023				92,358,549
Beginning balance (in shares) at Dec. 31, 2023			52,284
Beginning balance at Dec. 31, 2023	$ 344.1	355.6	$ 0	$ 1	2,542.9	(86.3)	(97.9)	(2,004.1)	(11.5)
Beginning balance (in shares) at Dec. 31, 2023	92,689,864			92,689,864
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 238	244.3						244.3	(6.3)
Other comprehensive (loss) income	(0.2)	(0.2)					(0.2)
Share-based compensation (in shares)				44,663
Share-based compensation	1.8	1.8			1.8
Conversion of preferred stock to common stock (in shares)			(46)	4,562
Noncontrolling interest	(0.8)								(0.8)
Ending balance (in shares) at Jun. 30, 2024			52,238
Ending balance at Jun. 30, 2024	$ 582.9	601.5	$ 0	$ 1	2,544.7	(86.3)	(98.1)	(1,759.8)	(18.6)
Ending balance (in shares) at Jun. 30, 2024	92,739,089			92,739,089
Beginning balance (in shares) at Mar. 31, 2024			52,238
Beginning balance at Mar. 31, 2024	$ 587.1	601.5	$ 0	$ 1	2,543.7	(86.3)	(99.6)	(1,757.3)	(14.4)
Beginning balance (in shares) at Mar. 31, 2024				92,700,495
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(6.7)	(2.5)						(2.5)	(4.2)
Other comprehensive (loss) income	1.5	1.5					1.5
Share-based compensation (in shares)				38,594
Share-based compensation	1	1			1
Ending balance (in shares) at Jun. 30, 2024			52,238
Ending balance at Jun. 30, 2024	$ 582.9	$ 601.5	$ 0	$ 1	$ 2,544.7	$ (86.3)	$ (98.1)	$ (1,759.8)	$ (18.6)
Ending balance (in shares) at Jun. 30, 2024	92,739,089			92,739,089

General

General	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
General	General The accompanying unaudited interim consolidated financial statements of Century Aluminum Company should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2023. In management’s opinion, the unaudited interim consolidated financial statements reflect all adjustments, which are of a normal and recurring nature, that are necessary for a fair presentation of financial results for the interim periods presented. Operating results for the first six months of 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. Throughout this Form 10-Q, and unless expressly stated otherwise or as the context otherwise requires, "Century Aluminum", "Century", "the Company", "we", "us", "our" and "ours" refer to Century Aluminum Company and its consolidated subsidiaries. Our consolidated financial statements include the consolidated results of the Jamalco joint venture ("Jamalco"), 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 Sheets. Recently Issued Accounting Standards In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. ("ASU") 2023-07, "Improvements to Reportable Segment Disclosures." ("ASU 2023-07"). Among other changes, the ASU requires disclosure of significant segment expenses and extends certain annual disclosures to interim periods. The amendments in this ASU are effective for the Company beginning with its annual financial statements for the year ending December 31, 2024. Early adoption is permitted. The Company is currently evaluating the requirements of ASU 2023-07. In December 2023, the FASB issued ASU No. 2023-09 ("ASU 2023-09"), Improvements to Income Tax Disclosures. The guidance is intended to improve income tax disclosure requirements by requiring (i) consistent categories and greater disaggregation of information in the rate reconciliation and (ii) the disaggregation of income taxes paid by jurisdiction. The ASU is effective for the Company beginning with its annual financial statements for the year ending December 31, 2025, with early adoption permitted, and is required to be applied prospectively with the option of retrospective application. The Company is currently evaluating the requirements of ASU 2023-09.

Acquisition of Jamalco

Acquisition of Jamalco	6 Months Ended
	Jun. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Acquisition of Jamalco	Acquisition of Jamalco On May 2, 2023, our wholly-owned subsidiary, Century Aluminum Jamaica Holdings, Inc. ("CAJH"), completed the acquisition of all the outstanding share capital of General Alumina Holdings Limited ("GAHL"), the indirect holder of a 55% interest in Jamalco, an unincorporated joint venture engaged in bauxite mining and alumina production in Jamaica. The remaining 45% interest in Jamalco is owned by CAP, which is owned by the Government of Jamaica. The results of operations have been included in the consolidated financial statements since the acquisition date. The purchase price of the acquisition was $1.00, primarily 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 six months ended June 30, 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 recognized bargain purchase gain of $273.4 million as of December 31, 2023 to $245.9 million as of March 31, 2024. The Company finalized its purchase accounting as of March 31, 2024. The following table represents the allocation of the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition: Purchase price allocation Amount Identifiable assets acquired and liabilities assumed 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 - net 217.2 Other assets 26.1 Accounts payable, trade (94.6) Accrued and other current liabilities (29.5) Other liabilities (36.5) Asset retirement obligation (23.9) Total identifiable net assets acquired and liabilities assumed 242.7 Less: noncontrolling interest (3.2) Bargain purchase gain $ 245.9 The following unaudited pro forma financial information reflects the results of operations of the Company for the three and six months ended June 30, 2023 as if the acquisition of Jamalco had been completed on January 1, 2023. 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, 2023, nor is the information indicative of future results of operations of the combined companies. Three months ended June 30, 2023 Six months ended June 30, 2023 Revenue $ 595.3 $ 1,177.6 Earnings 6.7 (33.0)

Curtailment of Operations - Haw

Curtailment of Operations - Hawesville	6 Months Ended
	Jun. 30, 2024
Restructuring and Related Activities [Abstract]
Curtailment of Operations - Hawesville	Curtailment of Operations - Hawesville In August 2022, we fully curtailed production at the Hawesville facility and expect to continue to maintain the plant with the intention of restarting operations when market conditions permit, including energy prices returning to more normalized levels and aluminum prices maintaining levels that can support the on-going costs and capital expenditures necessary to restart and operate the plant.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The significant related party transactions occurring during the three and six months ended June 30, 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 June 30, 2024 , Glencore plc and its affiliates (together "Glencore") beneficially owned 42.9% of Century’s outstanding common stock (45.9% on a fully-diluted basis assuming the conversion of all of the Series A Convertible Preferred Stock) and all of our outstanding Series A Convertible Preferred Stock. See Note 8. Shareholders' Equity for a description of our outstanding Series A Convertible Preferred 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 three months ended June 30, 2024 and 2023, we derived approximately 58% and 74% of our consolidated net sales from Glencore, respectively. For the six months ended June 30, 2024 and 2023, we derived approximately 61% and 74% of our consolidated net 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 primarily 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 three and six months ended June 30, 2024, the Company recogniz ed $50.3 million and $85.8 million, respectively, of revenue related to alumina sales to Glencore. For the three and six months ended June 30, 2023, we recorded $65.8 million and $86.8 million, respectively, of revenue related to alumina sales to Glencore. Purchases from Glencore We purchase a portion of our alumina and certain other raw material requirements from Glencore. Alumina purchases from Glencore during the three and six months ended June 30, 2024 and June 30, 2023, were priced based on published alumina and aluminum indices as well as fixed prices. Financial Contracts with Glencore We have certain financial contracts with Glencore. See Note 15. Derivatives regarding these forward financial sales contracts. Summary A summary of the aforementioned significant related party sales and purchases is as follows: Three months ended Six months ended 2024 2023 2024 2023 Net sales to Glencore $ 324.2 $ 427.2 $ 639.2 $ 839.4 Purchases from Glencore (1) 56.2 75.2 115.2 151.4 (1) Includes settlements of financial contract positions. Vlissingen Facility Agreement On December 9, 2022, Vlissingen entered into a Facility Agreement with Glencore International AG pursuant to which Vlissingen may borrow from time to time up to $90.0 million (the "Vlissingen Facility Agreement") in one or more loans at a fixed interest rate equal to 8.75% per annum and payable on December 2, 2024. See Note 11. Debt for additional information. Borrowings under the Vlissingen 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 ("Agreement") with an affiliate of 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 terms of the transaction permitted Grundartangi to repurchase the same number of Carbon Credits by December 21, 2023, at a price of €83.72 per Carbon Credit, for an aggregate amount of €32.7 million. In December 2023, the Agreement was amended ("Amended Agreement") to extend the repurchase window to March 25, 2024, and increased the repurchase price to €85.13 per Carbon Credit, for an aggregate amount of €33.2 million. In addition, Grundartangi entered into a second repurchase agreement ("Second Agreement") with Glencore to sell 40,000 Carbon Credits at a price of €69.30 per Carbon Credit and to repurchase the same number of Carbon Credits at a price of €70.71 per Carbon Credit by March 25, 2024 for an aggregate amount of €2.8 million. In March 2024, the Amended Agreement was amended to extend the repurchase window from March 25, 2024 to August 30, 2024 and the repurchase price was revised to €87.01 per Carbon Credit, for an aggregate amount of €33.9 million. In addition, the Second Agreement was amended to extend the repurchase window from March 25, 2024 to August 30, 2024 and revised the repurchase price to €72.59 per Carbon Credit, for an aggregate amount of €2.9 million. Due to the repurchase element of these transactions, the Company retains substantially all of the remaining benefits of the assets and has accounted for the transaction as a financing arrangement in accordance with Topic 606, Revenue from Contracts with Customers ("ASC 606").

Revenue

Revenue	6 Months Ended
	Jun. 30, 2024
Revenue Recognition and Deferred Revenue [Abstract]
Revenue	Revenue We disaggregate our revenue by geographical region as follows: Net Sales Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 United States $ 375.0 $ 363.2 $ 675.0 $ 705.5 Iceland 185.8 212.3 375.3 422.4 Total $ 560.8 $ 575.5 $ 1,050.3 $ 1,127.9 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 three and six months ended June 30, 2024 and 2023. Net Sales Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Aluminum $ 454.9 $ 509.7 $ 904.3 $ 1,041.1 Alumina 105.9 65.8 146.0 86.8 Total $ 560.8 $ 575.5 $ 1,050.3 $ 1,127.9 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 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. We have also entered into agreements with our customers to sell certain amounts of alumina at market-based prices. 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.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 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. Recurring Fair Value Measurements As of June 30, 2024 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 20.1 $ — $ — $ 20.1 Trust assets (1) 1.2 — — 1.2 Derivative instruments — 5.5 — 5.5 TOTAL $ 21.3 $ 5.5 $ — $ 26.8 LIABILITIES: Derivative instruments $ — $ 6.7 $ — $ 6.7 TOTAL $ — $ 6.7 $ — $ 6.7 Recurring Fair Value Measurements As of December 31, 2023 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 16.8 $ — $ — $ 16.8 Trust assets (1) 0.2 — — 0.2 Derivative instruments — 2.9 — 2.9 TOTAL $ 17.0 $ 2.9 $ — $ 19.9 LIABILITIES: Derivative instruments $ — $ 7.9 $ — $ 7.9 TOTAL $ — $ 7.9 $ — $ 7.9 (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 for fair value measurements categorized within Level 2 of the fair value hierarchy: Level 2 Fair Value Measurements: Asset / Liability Valuation Techniques Inputs LME forward financial sales contracts Discounted cash flows Quoted LME forward market Midwest Premium ("MWP") forward financial sales contracts Discounted cash flows Quoted MWP forward market Fixed for floating swaps Discounted cash flows Quoted LME forward market, quoted MWP forward market FX swaps Discounted cash flows Euro/USD forward exchange rate Indiana Hub power price swaps Discounted cash flows Quoted Indiana Hub forward market Casthouse currency hedges Discounted cash flows Euro/USD forward exchange rate; ISK/USD forward exchange rate Heavy Fuel Oil ("HFO") price swaps Discounted cash flows Quoted HFO forward market 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. The following table presents the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis. There was no activity related to Level 3 assets and liabilities measured at fair value on a recurring basis for the three and six months ended June 30, 2024. Level 3 Assets Level 3 Liabilities For the six months ended June 30, 2023 LME Forward financial sales contracts LME forward financial sales contracts Balance as of January 1, 2023 $ 1.8 $ (4.6) Transfers out of Level 3 (1) (1.8) 4.6 Balance as of June 30, 2023 $ — $ — Change in unrealized gains (losses) (2) $ — $ — (1) Transfer out of Level 3 due to period of time remaining in derivative contract. (2) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts."

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic and diluted earnings per share ("EPS") amounts are calculated using the two-class method. Under the two-class method, net earnings are allocated to each class of common stock and participating securities as if all of the net earnings for the period had been distributed. Basic earnings per common share excludes dilution and is calculated by dividing net income (loss) allocated to common stockholders by the weighted average number of common shares outstanding during the period. Diluted EPS amounts assume the issuance of common stock for all potentially dilutive securities. Prior to the three months ended March 31, 2024, diluted EPS amounts were calculated by applying the if-converted method as net income allocated to participating securities was not significant. The following table shows the basic and diluted (loss) earnings per share: For the three months ended June 30, 2024 2023 Net Income (Loss) Shares (in millions) $ Per Share Net Income (Loss) Shares (in millions) $ Per Share Net income (loss) attributable to Century stockholders $ (2.5) $ 7.5 Less: net income allocated to participating securities — 0.4 Basic EPS: Net income (loss) allocated to common stockholders $ (2.5) 92.7 $ (0.03) $ 7.1 92.3 $ 0.08 Effect of Dilutive Securities (1) : Share-based compensation — — (0.2) 0.9 Convertible senior notes — — — — Diluted EPS: Net income (loss) allocated to common stockholders $ (2.5) 92.7 $ (0.03) $ 6.9 93.2 $ 0.07 For the six months ended June 30, 2024 2023 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net (loss) income attributable to Century stockholders $ 244.3 $ (31.1) Less: net income allocated to participating securities 13.0 — Basic EPS: Net (loss) income allocated to common stockholders $ 231.3 92.7 $ 2.50 $ (31.1) 92.3 $ (0.34) Effect of Dilutive Securities (1) : Share-based compensation (12.2) 1.5 — — Convertible senior notes 2.6 4.6 — — Diluted EPS: Net (loss) income allocated to common stockholders with assumed conversion $ 221.7 98.8 $ 2.24 $ (31.1) 92.3 $ (0.34) Three months ended Six months ended Securities excluded from the calculation of diluted EPS (in millions) (1) : 2024 2023 2024 2023 Share-based compensation 1.9 — — 0.9 Convertible preferred shares 5.2 5.4 5.2 5.4 Convertible notes 4.6 4.6 — 4.6 (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.

Shareholders_ Equity

Shareholders’ Equity	6 Months Ended
	Jun. 30, 2024
Stockholders' Equity Note [Abstract]
Shareholders’ Equity	Shareholders’ Equity Common Stock As of June 30, 2024 and December 31, 2023, we had 195,000,000 shares of common stock, $0.01 par value per share, authorized under our Restated Certificate of Incorporation, of which 99,925,610 shares were issued and 92,739,089 shares were outstanding at June 30, 2024, and 99,876,385 were issued and 92,689,864 shares were outstanding at December 31, 2023. 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 June 30, 2024 and December 31, 2023, we had 5,000,000 shares of preferred stock, $0.01 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, liquidating 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. At June 30, 2024 and December 31, 2023, 52,238 and 52,284 shares of Series A Convertible Preferred Stock were outstanding, respectively. Glencore holds all of the issued and outstanding Series A Convertible Preferred Stock. The issuance of common stock under our stock incentive programs, debt exchange transactions and any stock offering that excludes Glencore participation triggers anti-dilution provisions of the preferred stock agreement and results in the automatic conversion of Series A Convertible Preferred Stock shares into shares of common stock. The conversion of preferred to common shares is 100 shares of common stock for each share of preferred stock. Our Series A Convertible Preferred Stock has a par value of $0.01 per share. Stock Repurchase Program In 2011, our Board of Directors authorized a $60.0 million common 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 convertible 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 June 30, 2024 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 June 30, 2024.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the three months ended June 30, 2024 and 2023, we recorded an income tax expense of $0.5 million and a tax benefit of $10.0 million, respectively. For the six months ended June 30, 2024 and 2023, we recorded an income tax expense of $1.0 million and a tax benefit of $10.2 million, respectively. The change is primarily due to changes in pretax income amounts and jurisdictional mix on a year over year basis. Our income tax expense or benefit for interim periods is determined using an estimate of our annual effective tax rate, adjusted for discrete items. The application of the accounting requirements for income taxes in interim periods, after consideration of our valuation allowance on domestic losses, causes a significant variation in the typical relationship between income tax expense/benefit and pre-tax accounting income/loss as reported on the Consolidated Statement of Operations. As of June 30, 2024, all of Century's U.S. and certain foreign deferred tax assets, net of deferred tax liabilities, continue to be subject to a valuation allowance. 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 December 14, 2023, the U.S. Department of the Treasury and the Internal Revenue Service released proposed rules to provide guidance on the production tax credit requirements under Internal Revenue Code Section 45X (the “Proposed Regulations”). The Proposed Regulations provide guidance on rules that taxpayers must satisfy to qualify for the IRA Section 45X tax credit. For the three and six months ended June 30, 2024, the Company recognized a reduction of $10.7 million and $22.6 million in Cost of goods sold and a reduction of $0.5 million and $1.2 million

Inventories

Inventories	6 Months Ended
	Jun. 30, 2024
Inventory, Net [Abstract]
Inventories	Inventories Inventories consist of the following: June 30, 2024 December 31, 2023 Raw materials $ 113.0 $ 162.5 Work-in-process 49.0 42.9 Finished goods 53.2 46.3 Operating and other supplies 252.3 225.3 Total inventories $ 467.5 $ 477.0 Inventories are stated at the lower of cost or Net Realizable Value ("NRV") using the first-in, first-out or the weighted average cost method.

Debt

Debt	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Debt	Debt June 30, 2024 December 31, 2023 Debt classified as current liabilities: Hancock County industrial revenue bonds ("IRBs") due April 1, 2028 , interest payable quarterly (variable interest rates (not to exceed 12%) ) (1) $ 7.8 $ 7.8 U.S. Revolving Credit Facility (2) — 23.7 Iceland Revolving Credit Facility (3) — — Grundartangi Casthouse Facility (4) 11.3 5.5 Iceland Term Facility — 1.3 Vlissingen Facility Agreement (5) 10.0 10.0 Debt classified as non-current liabilities: Grundartangi casthouse facility, net of financing fees of $0.0 million at June 30, 2024 (4) 118.7 98.8 7.5% senior secured notes due April 1, 2028, net of financing fees of $2.3 million at June 30, 2024, interest payable semiannually 247.7 247.4 2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.3 million at June 30, 2024, interest payable semiannually 84.9 84.7 Total $ 480.4 $ 479.2 (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 June 30, 2024 was 4.14% . (2) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 was 9.25% . (3) We incur interest at base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 wa s 8.84%. (4) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 was 8.88%. (5) We incur interest at a fixed rate equal to 8.75%. 7.5% Senior Secured Notes due 2028 In April 2021, we issued $250.0 million in aggregate principal amount of 7.5% senior secured notes due April 1, 2028 (the "2028 Notes"). We received proceeds of $245.2 million, after payment of certain financing fees and related expenses. The 2028 Notes bear interest semi-annually in arrears on April 1 and October 1 of each year, which began on October 1, 2021, at a rate of 7.5% per annum in cash. The 2028 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. We are in compliance with all applicable covenants under the indenture governing our Senior Notes as of June 30, 2024. As of June 30, 2024, the total estimated fair value of the 2028 Notes was $252.6 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. 2.75% Convertible Notes due 2028 In April 2021, we completed a private offering of $86.3 million aggregate principal amount of convertible senior notes due May 1, 2028 unless earlier converted, repurchased, or redeemed (the "Convertible Notes"). The Convertible Notes were issued at a price of 100% of their aggregate principal amount. We received proce eds of $83.7 million, a fter payment of certain financing fees and related expenses. The Convertible Notes bear interest semi-annually in arrears on May 1 and November 1 of each year, which began on November 1, 2021, at a rate of 2.75% per annum in cash. 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. As of June 30, 2024, the conversion rate remains unchanged. 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. As of June 30, 2024, the if-converted value of the Convertible Note s does not exceed the outstanding principal amount. As of June 30, 2024, the total estimated fair value of the Convertible Notes was $94.7 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 We and certain of our direct and indirect domestic subsidiaries have a senior secured revolving credit facility with a syndicate of lenders (as amended from time to time, 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 in the aggregate, including up to $150.0 million under a letter of credit sub-facility. The U.S. revolving credit facility matures on June 14, 2027. 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. We are in compliance with all applicable covenants as of June 30, 2024. 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 June 30, 2024, there were no outstanding borrowings and $40.8 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. Status of our U.S. revolving credit facility: June 30, 2024 Credit facility maximum amount $ 250.0 Borrowing availability 162.1 Outstanding letters of credit issued 40.8 Outstanding borrowings — Borrowing availability, net of outstanding letters of credit and borrowings 121.3 Iceland Revolving Credit Facility Our wholly-owned subsidiary, Nordural Grundartangi ehf ("Grundartangi"), entered into a revolving credit facility agreement with Landsbankinn hf., dated November 2013, as amended (the "Iceland revolving credit facility"), which originally provided for borrowings of up to $50.0 million in the aggregate. On February 4, 2022, we amended the Iceland revolving credit facility and increased the facility amount to $80.0 million. On September 28, 2022, we further amended the Iceland revolving credit facility and increased the facility amount 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 June 30, 2024, there were no outstanding borrowings under our Iceland revolving credit facility. The Iceland revolving credit facility has a term through December 2026. Our Iceland revolving credit facility contains a covenant that requires Grundartangi to maintain a minimum equity ratio. As of June 30, 2024, we were in compliance with all such covenants. Status of our Iceland revolving credit facility: June 30, 2024 Credit facility maximum amount $ 100.0 Borrowing availability 100.0 Outstanding letters of credit issued — Outstanding borrowings — Borrowing availability, net of borrowings 100.0 Grundartangi Casthouse Facility On November 2, 2021, in connection with the casthouse project at Grundartangi, we entered into an eight-year Term Facility Agreement with Arion Bank hf, to provide for borrowings up to $130.0 million (the "Casthouse Facility"). Under the Casthouse Facility, repayments of principal amounts will be made in equal quarterly installments equal to 1.739% of the principal amount, the first payment occurring in July 2024, with the remaining 60% of the principal amount to be paid no later than the termination date in December 2029. As of June 30, 2024, there were $130.0 million in outstanding borrowings under the Casthouse Facility. The Casthouse Facility also contains customary covenants, including restrictions on mergers and acquisitions, indebtedness, preservation of assets, and dispositions of assets and contains a covenant that requires Grundartangi to maintain a minimum equity ratio. As of June 30, 2024, we were in compliance with all such covenants. Iceland Term Facility Our wholly-owned subsidiary, Grundartangi, entered into a Term Facility Agreement with Arion Bank hf, dated September 2022, (the "Iceland Term Facility") to provide for borrowings up to €13.6 million. Repayments of principal amounts were made in equal monthly installments, the first payment occurring in February 2023, with the remainder of the principal amount paid in January 2024. Borrowings under the Iceland Term Facility bore interest at a rate equal to 3.2% plus EUR EURIBOR 1 month as published at any time by the European Money Markets Institute. The Iceland Term Facility has been repaid in full and has terminated pursuant to its terms in the first quarter of 2024. Vlissingen Facility Agreement On December 9, 2022, Vlissingen entered into a Facility Agreement with Glencore International AG pursuant to which Vlissingen may borrow from time to time up to $90.0 million (the "Vlissingen Facility Agreement") in one or more loans at a fixed interest rate equal to 8.75% per annum and payable on December 2, 2024, the maturity date of the Vlissingen Facility Agreement. As of June 30, 2024, there were $10.0 million in outstanding borrowings under the Vlissingen Facility Agreement. The Vlissingen Facility Agreement contains customary covenants, including with respect to mergers, guarantees and preservation and dispositions of assets. As of June 30, 2024, we were in compliance with all such covenants Hancock County Industrial Revenue Bond s 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 June 30, 2024, 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.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 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 which 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 ten 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 June 30, 2024, $2.0 million was recorded in Other current liabilities and $3.5 million was recorded in Other liabilities on the Consolidated Balance Sheets. PBGC Settlement In 2013, we entered into a settlement agreement with the Pension Benefit Guaranty Corporation (the "PBGC") regarding an alleged "cessation of operations" at our Ravenswood f acility (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. In October 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 the next 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 June 30, 2024, we made contributions of $6.9 million and no payments related to the Amended PBGC Settlement Agreement. Comparatively, as of June 30, 2023, we made contributions of $2.4 million related to the Amended PBGC Settlement Agreement. Power Commitments and Contingencies Hawesville Hawesville has a power supply arrangement with Kenergy and Century Marketer, LLC (“Century Marketer"), Century's wholly-owned subsidiary that acts as a MISO market participant. Under this arrangement, Hawesville gets access to power at Midcontinent Independent System Operator ("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 Hawesville. 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 Hawesville has a term through December 31, 2025, with automatic one-year extensions unless either party provides one-year notice of termination prior to the December 31 anniversary date. Sebree Sebree has a power supply arrangement with Kenergy and Century Marketer. Under this arrangement, Sebree gets access to power at Midcontinent Independent System Operator ("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, 2025, 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 ("CASC") has a power supply agreement with Santee Cooper that has an effective term through December 2026. 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 of aggregate power 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. Under the terms of the Landsvirkjun agreement, Landsvirkjun will provide up to 182 MW over time to support the most recent capacity creep requirements and the new billet casthouse at Grundartangi. The Landsvirkjun agreement provides for fixed rates on most of the 182 MW, with a variable rate applicable to a smaller portion of the power through December 31, 2026. Grundartangi also has a separate 25 MW power purchase agreement with Landsvirkjun at 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 59% of our total workforce. Approximately 87% 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, 2024. 100% of Vlissingen's work force 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, 2025. Approximately 38% of our U.S. based work force is represented by USW through separately negotiated labor agreements for each facility. The labor agreement for Hawesville employees is effective through April 1, 2026. Upon announcement of the temporary curtailment, Hawesville and the USW local union entered into effects bargaining. An agreement was reached on July 19, 2022, covering the curtailment period. Century Sebree's labor agreement with the USW for its employees is effective through October 28, 2028. Mt. Holly employees are not represented by a labor union. Approximately 61% of Jamalco’s work force is represented by the Union of Technical, Administrative, and Supervisory Personnel ("UTASP") through separately negotiated 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. Contingent obligations 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 June 30, 2024, the principal and accrued interest for the contingent obligation was $31.6 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. As of June 30, 2024, the LME forward market prices do not exceed the threshold for payment. In addition, based on the current level of Hawesville's operations, including the temporary curtailment, 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.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss ("AOCL")	6 Months Ended
	Jun. 30, 2024
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Loss ("AOCL")	Accumulated Other Comprehensive Loss ("AOCL") Components of AOCL: June 30, 2024 December 31, 2023 Defined benefit plan liabilities $ (101.8) $ (101.8) Unrealized gain on financial instruments 1.4 1.6 Other comprehensive loss before income tax effect (100.4) (100.2) Income tax effect (1) 2.3 2.3 Accumulated other comprehensive loss $ (98.1) $ (97.9) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: June 30, 2024 December 31, 2023 Defined benefit plan liabilities $ 2.6 $ 2.6 Unrealized gain on financial instruments (0.3) (0.3) The following table summarizes the changes in the accumulated balances for each component of AOCL: Defined benefit plan and other postretirement liabilities Unrealized gain on financial instruments Total, net of tax Balance, March 31, 2024 $ (101.0) $ 1.4 $ (99.6) Net amount reclassified to net income (loss) 1.5 — 1.5 Balance, June 30, 2024 $ (99.5) $ 1.4 $ (98.1) Balance, March 31, 2023 $ (94.4) $ 1.5 $ (92.9) Net amount reclassified to net income (loss) 2.2 — 2.2 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, December 31, 2023 $ (99.4) $ 1.5 $ (97.9) Other comprehensive loss before reclassifications (3.4) — (3.4) Net amount reclassified to net income (loss) $ 3.3 $ (0.1) $ 3.2 Balance, June 30, 2024 $ (99.5) $ 1.4 $ (98.1) Balance, December 31, 2022 $ (95.6) $ 1.6 $ (94.0) Net amount reclassified to net income (loss) 3.4 (0.1) 3.3 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended Six months ended AOCL Components Location 2024 2023 2024 2023 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 0.7 $ 1.4 $ 1.6 $ 2.2 Selling, general and administrative expenses 0.1 0.1 0.3 0.3 Other operating expense - net 0.7 0.7 1.4 0.9 Income tax effect — — — — Net of tax $ 1.5 $ 2.2 $ 3.3 $ 3.4 Unrealized gain (loss) on financial instruments Cost of goods sold $ — $ — $ (0.1) $ (0.1) Income tax effect — — — — Net of tax $ — $ — $ (0.1) $ (0.1)

Components of Net Periodic Bene

Components of Net Periodic Benefit Cost	6 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost Pension Benefits Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Service cost $ 0.7 $ 0.1 $ 1.3 $ 1.1 Interest cost 3.2 4.4 6.7 7.0 Expected return on plan assets (4.1) (1.7) (7.9) (7.5) Amortization of prior service costs — — 0.1 0.1 Amortization of net loss 1.3 2.4 3.0 3.2 Net periodic benefit cost (income) $ 1.1 $ 5.2 $ 3.2 $ 3.9 Other Postretirement Benefits Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Service cost $ 0.1 $ — $ 0.1 $ 0.1 Interest cost 0.9 1.2 1.9 1.9 Amortization of prior service cost (0.1) — (0.1) — Amortization of net loss 0.3 (0.2) 0.3 0.1 Net periodic benefit cost $ 1.2 $ 1.0 $ 2.2 $ 2.1

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives As of June 30, 2024, we had an open position of 42,654 tonnes re lated to LME forward financial sales contracts to fix the forward LME aluminum price. These contracts are expected to settle monthly through July 2025. We also had an open position of 25,200 tonnes related to MWP forward financial sales contracts to fix the forward MWP price. These contracts are expected to settle monthly through July 2025. 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 June 30, 2024, we had no open fixed for floating swaps. We have entered into forward contracts to hedge the risk of fluctuations associated with the Icelandic Krona (ISK) and Euro for contracts related to the construction of the Grundartangi casthouse denominated in these currencies ("casthouse currency hedges"). As of June 30, 2024, we had no open casthouse currency hedges. We have entered into financial contracts to hedge a portion of our exposure at our operations to the NYMEX Henry Hub (“NYMEX Henry Hub natural gas price swaps”). The natural gas volume is measured per million British Thermal Units ("MMBtu"). As of June 30, 2024 we had no open NYMEX Henry Hub natural gas price 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 June 30, 2024, we had an open position of 240,000 barrels. The HFO price swaps are expected to settle monthly through May 2025. 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 June 30, 2024, we had an open position of 460,080 MWh. The Indiana Hub power price swaps are expected to settle monthly through July 2025. 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 June 30, 2024 and December 31, 2023, the Company had not recorded restricted cash as collateral related to open derivative contracts under the master arrangements with our counterparties. The following tables set forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of June 30, 2024 and December 31, 2023, respectively: Asset Fair Value June 30, 2024 December 31, 2023 Commodity contracts (1) $ 5.5 $ 2.9 Liability Fair Value June 30, 2024 December 31, 2023 Commodity contracts (1) $ 6.7 $ 7.8 Foreign exchange contracts (2) — 0.1 Total $ 6.7 $ 7.9 (1) Commodity contracts reflect our outstanding LME and MWP forward financial sales contracts, Indy Hub power price swaps, fixed for floating swaps, NYMEX Henry Hub natural gas price swaps, and HFO price swaps. At June 30, 2024, $4.0 million of Due to affiliates was related to commodity contracts with Glencore. At December 31, 2023, $6.4 million of Due to affiliates was related to commodity contract liab ilities with Glencore. (2) Foreign exchange contracts reflect our outstanding FX swaps and the casthouse currency hedges. The following table summarizes the net (loss) gain on forward and derivative contracts: Three months ended Six months ended 2024 2023 2024 2023 Commodity contracts (1) $ (4.0) $ 9.1 $ 3.5 $ (50.1) Foreign exchange contracts — 0.0 (0.1) 1.6 Total $ (4.0) $ 9.1 $ 3.4 $ (48.5) (1) For the three months ended June 30, 2024, $1.9 million of the net loss was with Glencore, and for the three months ended June 30, 2023, $11.4 million of the net gain was with Glencore. Comparatively, for the six months ended June 30, 2024 $2.5 million of the net gain was with Glencore, and for the six months ended June 30, 2023 $3.5 million of the net loss was with Glencore.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net income (loss) attributable to Century stockholders	$ (2.5)	$ 7.5	$ 244.3	$ (31.1)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2024
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

General (Policies)

General (Policies)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Recently Issued Accounting Standards	Recently Issued Accounting Standards In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. ("ASU") 2023-07, "Improvements to Reportable Segment Disclosures." ("ASU 2023-07"). Among other changes, the ASU requires disclosure of significant segment expenses and extends certain annual disclosures to interim periods. The amendments in this ASU are effective for the Company beginning with its annual financial statements for the year ending December 31, 2024. Early adoption is permitted. The Company is currently evaluating the requirements of ASU 2023-07. In December 2023, the FASB issued ASU No. 2023-09 ("ASU 2023-09"), Improvements to Income Tax Disclosures. The guidance is intended to improve income tax disclosure requirements by requiring (i) consistent categories and greater disaggregation of information in the rate reconciliation and (ii) the disaggregation of income taxes paid by jurisdiction. The ASU is effective for the Company beginning with its annual financial statements for the year ending December 31, 2025, with early adoption permitted, and is required to be applied prospectively with the option of retrospective application. The Company is currently evaluating the requirements of ASU 2023-09.

Acquisition of Jamalco (Tables)

Acquisition of Jamalco (Tables)	6 Months Ended
	Jun. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Schedule of Fair Value of Assets Acquired and Liabilities Assumed	The following table represents the allocation of the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition: Purchase price allocation Amount Identifiable assets acquired and liabilities assumed 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 - net 217.2 Other assets 26.1 Accounts payable, trade (94.6) Accrued and other current liabilities (29.5) Other liabilities (36.5) Asset retirement obligation (23.9) Total identifiable net assets acquired and liabilities assumed 242.7 Less: noncontrolling interest (3.2) Bargain purchase gain $ 245.9
Schedule of Unaudited Pro Forma Financial Information	The following unaudited pro forma financial information reflects the results of operations of the Company for the three and six months ended June 30, 2023 as if the acquisition of Jamalco had been completed on January 1, 2023. 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, 2023, nor is the information indicative of future results of operations of the combined companies. Three months ended June 30, 2023 Six months ended June 30, 2023 Revenue $ 595.3 $ 1,177.6 Earnings 6.7 (33.0)

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	A summary of the aforementioned significant related party sales and purchases is as follows: Three months ended Six months ended 2024 2023 2024 2023 Net sales to Glencore $ 324.2 $ 427.2 $ 639.2 $ 839.4 Purchases from Glencore (1) 56.2 75.2 115.2 151.4 (1) Includes settlements of financial contract positions.

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2024
Revenue Recognition and Deferred Revenue [Abstract]
Schedule of Disaggregation of revenue	Net Sales Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 United States $ 375.0 $ 363.2 $ 675.0 $ 705.5 Iceland 185.8 212.3 375.3 422.4 Total $ 560.8 $ 575.5 $ 1,050.3 $ 1,127.9 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 three and six months ended June 30, 2024 and 2023. Net Sales Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Aluminum $ 454.9 $ 509.7 $ 904.3 $ 1,041.1 Alumina 105.9 65.8 146.0 86.8 Total $ 560.8 $ 575.5 $ 1,050.3 $ 1,127.9

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Schedule of financial assets and liabilities at fair value on a recurring basis	Recurring Fair Value Measurements As of June 30, 2024 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 20.1 $ — $ — $ 20.1 Trust assets (1) 1.2 — — 1.2 Derivative instruments — 5.5 — 5.5 TOTAL $ 21.3 $ 5.5 $ — $ 26.8 LIABILITIES: Derivative instruments $ — $ 6.7 $ — $ 6.7 TOTAL $ — $ 6.7 $ — $ 6.7 Recurring Fair Value Measurements As of December 31, 2023 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 16.8 $ — $ — $ 16.8 Trust assets (1) 0.2 — — 0.2 Derivative instruments — 2.9 — 2.9 TOTAL $ 17.0 $ 2.9 $ — $ 19.9 LIABILITIES: Derivative instruments $ — $ 7.9 $ — $ 7.9 TOTAL $ — $ 7.9 $ — $ 7.9 (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.
Schedule of valuation methodology for assets and liabilities at fair value	The following section describes the valuation techniques and inputs for fair value measurements categorized within Level 2 of the fair value hierarchy: Level 2 Fair Value Measurements: Asset / Liability Valuation Techniques Inputs LME forward financial sales contracts Discounted cash flows Quoted LME forward market Midwest Premium ("MWP") forward financial sales contracts Discounted cash flows Quoted MWP forward market Fixed for floating swaps Discounted cash flows Quoted LME forward market, quoted MWP forward market FX swaps Discounted cash flows Euro/USD forward exchange rate Indiana Hub power price swaps Discounted cash flows Quoted Indiana Hub forward market Casthouse currency hedges Discounted cash flows Euro/USD forward exchange rate; ISK/USD forward exchange rate Heavy Fuel Oil ("HFO") price swaps Discounted cash flows Quoted HFO forward market
Schedule of fair value reconciliation of Level 3 assets and liabilities measured at fair value	The following table presents the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis. There was no activity related to Level 3 assets and liabilities measured at fair value on a recurring basis for the three and six months ended June 30, 2024. Level 3 Assets Level 3 Liabilities For the six months ended June 30, 2023 LME Forward financial sales contracts LME forward financial sales contracts Balance as of January 1, 2023 $ 1.8 $ (4.6) Transfers out of Level 3 (1) (1.8) 4.6 Balance as of June 30, 2023 $ — $ — Change in unrealized gains (losses) (2) $ — $ — (1) Transfer out of Level 3 due to period of time remaining in derivative contract. (2) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts."

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2024
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 (loss) earnings per share: For the three months ended June 30, 2024 2023 Net Income (Loss) Shares (in millions) $ Per Share Net Income (Loss) Shares (in millions) $ Per Share Net income (loss) attributable to Century stockholders $ (2.5) $ 7.5 Less: net income allocated to participating securities — 0.4 Basic EPS: Net income (loss) allocated to common stockholders $ (2.5) 92.7 $ (0.03) $ 7.1 92.3 $ 0.08 Effect of Dilutive Securities (1) : Share-based compensation — — (0.2) 0.9 Convertible senior notes — — — — Diluted EPS: Net income (loss) allocated to common stockholders $ (2.5) 92.7 $ (0.03) $ 6.9 93.2 $ 0.07 For the six months ended June 30, 2024 2023 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net (loss) income attributable to Century stockholders $ 244.3 $ (31.1) Less: net income allocated to participating securities 13.0 — Basic EPS: Net (loss) income allocated to common stockholders $ 231.3 92.7 $ 2.50 $ (31.1) 92.3 $ (0.34) Effect of Dilutive Securities (1) : Share-based compensation (12.2) 1.5 — — Convertible senior notes 2.6 4.6 — — Diluted EPS: Net (loss) income allocated to common stockholders with assumed conversion $ 221.7 98.8 $ 2.24 $ (31.1) 92.3 $ (0.34) Three months ended Six months ended Securities excluded from the calculation of diluted EPS (in millions) (1) : 2024 2023 2024 2023 Share-based compensation 1.9 — — 0.9 Convertible preferred shares 5.2 5.4 5.2 5.4 Convertible notes 4.6 4.6 — 4.6 (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.

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Jun. 30, 2024
Inventory, Net [Abstract]
Schedule of inventories	Inventories consist of the following: June 30, 2024 December 31, 2023 Raw materials $ 113.0 $ 162.5 Work-in-process 49.0 42.9 Finished goods 53.2 46.3 Operating and other supplies 252.3 225.3 Total inventories $ 467.5 $ 477.0

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Schedule of debt	June 30, 2024 December 31, 2023 Debt classified as current liabilities: Hancock County industrial revenue bonds ("IRBs") due April 1, 2028 , interest payable quarterly (variable interest rates (not to exceed 12%) ) (1) $ 7.8 $ 7.8 U.S. Revolving Credit Facility (2) — 23.7 Iceland Revolving Credit Facility (3) — — Grundartangi Casthouse Facility (4) 11.3 5.5 Iceland Term Facility — 1.3 Vlissingen Facility Agreement (5) 10.0 10.0 Debt classified as non-current liabilities: Grundartangi casthouse facility, net of financing fees of $0.0 million at June 30, 2024 (4) 118.7 98.8 7.5% senior secured notes due April 1, 2028, net of financing fees of $2.3 million at June 30, 2024, interest payable semiannually 247.7 247.4 2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.3 million at June 30, 2024, interest payable semiannually 84.9 84.7 Total $ 480.4 $ 479.2 (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 June 30, 2024 was 4.14% . (2) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 was 9.25% . (3) We incur interest at base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 wa s 8.84%. (4) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2024 was 8.88%. (5) We incur interest at a fixed rate equal to 8.75%.
Schedule of line of credit facilities	Status of our U.S. revolving credit facility: June 30, 2024 Credit facility maximum amount $ 250.0 Borrowing availability 162.1 Outstanding letters of credit issued 40.8 Outstanding borrowings — Borrowing availability, net of outstanding letters of credit and borrowings 121.3 Status of our Iceland revolving credit facility: June 30, 2024 Credit facility maximum amount $ 100.0 Borrowing availability 100.0 Outstanding letters of credit issued — Outstanding borrowings — Borrowing availability, net of borrowings 100.0

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss ("AOCL") (Tables)	6 Months Ended
	Jun. 30, 2024
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated balances for each component of AOCI	Components of AOCL: June 30, 2024 December 31, 2023 Defined benefit plan liabilities $ (101.8) $ (101.8) Unrealized gain on financial instruments 1.4 1.6 Other comprehensive loss before income tax effect (100.4) (100.2) Income tax effect (1) 2.3 2.3 Accumulated other comprehensive loss $ (98.1) $ (97.9) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: June 30, 2024 December 31, 2023 Defined benefit plan liabilities $ 2.6 $ 2.6 Unrealized gain on financial instruments (0.3) (0.3) The following table summarizes the changes in the accumulated balances for each component of AOCL: Defined benefit plan and other postretirement liabilities Unrealized gain on financial instruments Total, net of tax Balance, March 31, 2024 $ (101.0) $ 1.4 $ (99.6) Net amount reclassified to net income (loss) 1.5 — 1.5 Balance, June 30, 2024 $ (99.5) $ 1.4 $ (98.1) Balance, March 31, 2023 $ (94.4) $ 1.5 $ (92.9) Net amount reclassified to net income (loss) 2.2 — 2.2 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, December 31, 2023 $ (99.4) $ 1.5 $ (97.9) Other comprehensive loss before reclassifications (3.4) — (3.4) Net amount reclassified to net income (loss) $ 3.3 $ (0.1) $ 3.2 Balance, June 30, 2024 $ (99.5) $ 1.4 $ (98.1) Balance, December 31, 2022 $ (95.6) $ 1.6 $ (94.0) Net amount reclassified to net income (loss) 3.4 (0.1) 3.3 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7)
Schedule of Reclassification out of AOCI	Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended Six months ended AOCL Components Location 2024 2023 2024 2023 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 0.7 $ 1.4 $ 1.6 $ 2.2 Selling, general and administrative expenses 0.1 0.1 0.3 0.3 Other operating expense - net 0.7 0.7 1.4 0.9 Income tax effect — — — — Net of tax $ 1.5 $ 2.2 $ 3.3 $ 3.4 Unrealized gain (loss) on financial instruments Cost of goods sold $ — $ — $ (0.1) $ (0.1) Income tax effect — — — — Net of tax $ — $ — $ (0.1) $ (0.1)

Components of Net Periodic Be_2

Components of Net Periodic Benefit Cost (Tables)	6 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Schedule of net periodic benefit cost	Pension Benefits Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Service cost $ 0.7 $ 0.1 $ 1.3 $ 1.1 Interest cost 3.2 4.4 6.7 7.0 Expected return on plan assets (4.1) (1.7) (7.9) (7.5) Amortization of prior service costs — — 0.1 0.1 Amortization of net loss 1.3 2.4 3.0 3.2 Net periodic benefit cost (income) $ 1.1 $ 5.2 $ 3.2 $ 3.9 Other Postretirement Benefits Three months ended June 30, Six months ended June 30, 2024 2023 2024 2023 Service cost $ 0.1 $ — $ 0.1 $ 0.1 Interest cost 0.9 1.2 1.9 1.9 Amortization of prior service cost (0.1) — (0.1) — Amortization of net loss 0.3 (0.2) 0.3 0.1 Net periodic benefit cost $ 1.2 $ 1.0 $ 2.2 $ 2.1

Derivatives (Tables)

Derivatives (Tables)	6 Months Ended
	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivatives not designated as hedging instruments	The following tables set forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of June 30, 2024 and December 31, 2023, respectively: Asset Fair Value June 30, 2024 December 31, 2023 Commodity contracts (1) $ 5.5 $ 2.9 Liability Fair Value June 30, 2024 December 31, 2023 Commodity contracts (1) $ 6.7 $ 7.8 Foreign exchange contracts (2) — 0.1 Total $ 6.7 $ 7.9 (1) Commodity contracts reflect our outstanding LME and MWP forward financial sales contracts, Indy Hub power price swaps, fixed for floating swaps, NYMEX Henry Hub natural gas price swaps, and HFO price swaps. At June 30, 2024, $4.0 million of Due to affiliates was related to commodity contracts with Glencore. At December 31, 2023, $6.4 million of Due to affiliates was related to commodity contract liab ilities with Glencore. (2) Foreign exchange contracts reflect our outstanding FX swaps and the casthouse currency hedges.
Schedule of derivative instruments	The following table summarizes the net (loss) gain on forward and derivative contracts: Three months ended Six months ended 2024 2023 2024 2023 Commodity contracts (1) $ (4.0) $ 9.1 $ 3.5 $ (50.1) Foreign exchange contracts — 0.0 (0.1) 1.6 Total $ (4.0) $ 9.1 $ 3.4 $ (48.5) (1) For the three months ended June 30, 2024, $1.9 million of the net loss was with Glencore, and for the three months ended June 30, 2023, $11.4 million of the net gain was with Glencore. Comparatively, for the six months ended June 30, 2024 $2.5 million of the net gain was with Glencore, and for the six months ended June 30, 2023 $3.5 million of the net loss was with Glencore.

Acquisition of Jamalco - Narrat

Acquisition of Jamalco - Narrative (Details) - USD ($)		3 Months Ended			6 Months Ended		12 Months Ended
	May 02, 2023	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Bargain purchase gain		$ 0		$ 0	$ 245,900,000	$ 0
General Alumina Holdings Limited
Business Acquisition [Line Items]
Payments to acquire business	$ 1
Bargain purchase gain			$ 245,900,000		$ 245,900,000		$ 273,400,000
Property, plant and equipment reduction			29,000,000
Purchase, gain reduction			$ 29,000,000
Jamalco | General Alumina Holdings Limited
Business Acquisition [Line Items]
Noncontrolling interest, ownership percentage by parent	55%
Jamalco | Clarendon Alumina Production Limited
Business Acquisition [Line Items]
Ownership percentage by noncontrolling owners	45%

Acquisition of Jamalco - Fair V

Acquisition of Jamalco - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023	May 02, 2023
Business Acquisition [Line Items]
Bargain purchase gain	$ 0	$ 273.4
General Alumina Holdings Limited
Business Acquisition [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 - net			217.2
Other assets			26.1
Accounts payable, trade			(94.6)
Accrued and other current liabilities			(29.5)
Other liabilities			(36.5)
Asset retirement obligation			(23.9)
Total identifiable net assets acquired and liabilities assumed			242.7
Less: noncontrolling interest			(3.2)
Bargain purchase gain			$ 245.9

Acquisition of Jamalco - Unaudi

Acquisition of Jamalco - Unaudited Pro Forma Financial Information (Details) - General Alumina Holdings Limited - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023
Business Acquisition [Line Items]
Revenue	$ 595.3	$ 1,177.6
Earnings	$ 6.7	$ (33)

Curtailment of Operations - H_2

Curtailment of Operations - Hawesville (Details) - Curtailment Of Operations - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restructuring Cost and Reserve [Line Items]
Severance costs	$ 1,700,000	$ 4,400,000	$ 2,400,000	$ 11,400,000
Gain (loss) on material sales	$ 0	500,000	$ 500,000	1,200,000
Temporary Facility Closing, Excess Capacity
Restructuring Cost and Reserve [Line Items]
Excess capacity charges		$ 3,600,000		$ 9,000,000

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) carbon_credit in Thousands, € in Millions, $ in Millions		1 Months Ended			3 Months Ended		6 Months Ended
	Dec. 21, 2023 EUR (€) € / carbonCredit	Mar. 31, 2024 EUR (€) € / carbonCredit	Dec. 31, 2023 EUR (€) carbon_credit € / carbonCredit	Sep. 30, 2023 EUR (€) carbon_credit € / carbonCredit	Jun. 30, 2024 USD ($) € / carbonCredit	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) € / carbonCredit	Jun. 30, 2023 USD ($)	Dec. 09, 2022 USD ($)
Related Party Transaction [Line Items]
Revenue | $					$ 560.8	$ 575.5	$ 1,050.3	$ 1,127.9
Vlissingen facility agreement | Affiliated Entity | Vlissingen
Related Party Transaction [Line Items]
Credit facility maximum amount | $									$ 90
Stated interest rate, percentage									8.75%
Carbon Credit Sale | Affiliated Entity | Grundartangi
Related Party Transaction [Line Items]
Carbon credit sold in transaction | carbon_credit				390
Sale price (Euro per carbon credit)				82.18
Aggregate amount | €				€ 32.1
Carbon Credit Repurchase | Affiliated Entity | Grundartangi
Related Party Transaction [Line Items]
Sale price (Euro per carbon credit)	83.72	87.01	85.13
Aggregate amount | €	€ 32.7	€ 33.9	€ 33.2
Second Repurchase Agreement, Carbon Credit Sale | Affiliated Entity | Grundartangi
Related Party Transaction [Line Items]
Carbon credit sold in transaction | carbon_credit			40
Sale price (Euro per carbon credit)			69.30
Second Repurchase Agreement, Carbon Credit Repurchase | Affiliated Entity | Grundartangi
Related Party Transaction [Line Items]
Sale price (Euro per carbon credit)			70.71		72.59		72.59
Aggregate amount | €		€ 2.9	€ 2.8
Supply Commitment | Glencore
Related Party Transaction [Line Items]
Revenue | $					$ 50.3	$ 65.8	$ 85.8	$ 86.8
Consolidated sales | Customer concentration risk | Glencore
Related Party Transaction [Line Items]
Major customer, percentage of revenue, net (percent)					58%	74%	61%	74%
Glencore
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners					42.90%		42.90%
Economic ownership percentage by related party					45.90%		45.90%

Related Party Transactions - Su

Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Related Party Transaction [Line Items]
Revenue	$ 560.8	$ 575.5	$ 1,050.3	$ 1,127.9
Related Party
Related Party Transaction [Line Items]
Revenue	324.2	427.2	639.2	839.4
Related Party | Glencore
Related Party Transaction [Line Items]
Revenue	324.2	427.2	639.2	839.4
Purchases from Glencore	$ 56.2	$ 75.2	$ 115.2	$ 151.4

Revenue - Breakdown of Revenue

Revenue - Breakdown of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 560.8	$ 575.5	$ 1,050.3	$ 1,127.9
Contract liabilities	42.4		42.4		$ 30.6
Aluminum
Disaggregation of Revenue [Line Items]
Revenue	454.9	509.7	904.3	1,041.1
Alumina
Disaggregation of Revenue [Line Items]
Revenue	105.9	65.8	146	86.8
United States
Disaggregation of Revenue [Line Items]
Revenue	375	363.2	675	705.5
Iceland
Disaggregation of Revenue [Line Items]
Revenue	$ 185.8	$ 212.3	$ 375.3	$ 422.4

Fair Value Measurements - Recur

Fair Value Measurements - Recurring Fair Value Measurements (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
ASSETS:
Cash equivalents	$ 20.1	$ 16.8
Trust assets	1.2	0.2
Derivative instruments	5.5	2.9
TOTAL	26.8	19.9
LIABILITIES:
Derivative instruments	6.7	7.9
TOTAL	6.7	7.9
Level 1
ASSETS:
Cash equivalents	20.1	16.8
Trust assets	1.2	0.2
Derivative instruments	0	0
TOTAL	21.3	17
LIABILITIES:
Derivative instruments	0	0
TOTAL	0	0
Level 2
ASSETS:
Cash equivalents	0	0
Trust assets	0	0
Derivative instruments	5.5	2.9
TOTAL	5.5	2.9
LIABILITIES:
Derivative instruments	6.7	7.9
TOTAL	6.7	7.9
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 - Level

Fair Value Measurements - Level 3 Reconciliation (Details) $ in Millions	6 Months Ended
	Jun. 30, 2023 USD ($)
LME Forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	$ 1.8
Transfers out of Level 3	(1.8)
Balance, ending	0
Change in unrealized gains (losses)	0
LME forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	(4.6)
Transfers out of Level 3	4.6
Balance, ending	0
Change in unrealized gains (losses)	$ 0

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Net income (loss) attributable to Century stockholders	$ (2.5)	$ 7.5	$ 244.3	$ (31.1)
Less: net income allocated to participating securities	0	0.4	13	0
Basic EPS:
Net income (loss) allocated to common stockholders	$ (2.5)	$ 7.1	$ 231.3	$ (31.1)
Net income (loss) allocated to common stockholders (in shares)	92.7	92.3	92.7	92.3
Net income (loss) allocated to common stockholders (in dollars per share)	$ (0.03)	$ 0.08	$ 2.50	$ (0.34)
Effect of Dilutive Securities
Share-based compensation	$ 0	$ (0.2)	$ (12.2)	$ 0
Share-based compensation (in shares)	0	0.9	1.5	0
Convertible senior notes	$ 0	$ 0	$ 2.6	$ 0
Convertible senior notes (in shares)	0	0	4.6	0
Diluted EPS:
Net income (loss) allocated to common stockholders	$ (2.5)	$ 6.9	$ 221.7	$ (31.1)
Net income (loss) allocated to common stockholders (in shares)	92.7	93.2	98.8	92.3
Net income (loss) allocated to common stockholders (in dollars per share)	$ (0.03)	$ 0.07	$ 2.24	$ (0.34)

Earnings Per Share - Securities

Earnings Per Share - Securities Excluded (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-based compensation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	1.9	0	0	0.9
Convertible preferred shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	5.2	5.4	5.2	5.4
Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	4.6	4.6	0	4.6

Shareholders_ Equity (Details)

Shareholders’ Equity (Details) - USD ($)	3 Months Ended	111 Months Ended
	Mar. 31, 2015	Jun. 30, 2024	Dec. 31, 2023	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)		99,925,610	99,876,385
Common stock, shares, outstanding (in shares)		92,739,089	92,689,864
Preferred stock, shares authorized (in shares)		5,000,000	5,000,000
Preferred stock par value (in dollars per share)		$ 0.01	$ 0.01
Number of shares issued for each share of preferred stock (in shares)		100
Stock repurchase program, authorized amount		$ 130,000,000		$ 60,000,000
Stock repurchase program, authorized, increase amount	$ 70,000,000
Treasury shares acquired (in shares)		7,186,521
Treasury stock, value		$ 86,300,000	$ 86,300,000
Treasury stock, shares, acquired (in shares)		0
Stock repurchase program, remaining authorized repurchase amount		$ 43,700,000
Convertible preferred shares
Class of Stock [Line Items]
Preferred stock par value (in dollars per share)		$ 0.01
Preferred shares issued (in shares)					160,000
Preferred shares outstanding (in shares)		52,238	52,284

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Income tax expense (benefit)	$ 0.5	$ (10)	$ 1	$ (10.2)
Reduction in cost of goods sold	(540.4)	(559.6)	(1,013.4)	(1,063.9)
Reduction in selling, general and administrative expenses	(12.3)	$ (12)	(26.4)	$ (25.4)
Manufacturing credit receivable, current	57.1		57.1		$ 59.3
Manufacturing credit receivable, noncurrent	26		26
Inflation Reduction Act
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reduction in cost of goods sold	10.7		22.6
Reduction in selling, general and administrative expenses	$ 0.5		$ 1.2

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Inventory, Net [Abstract]
Raw materials	$ 113	$ 162.5
Work-in-process	49	42.9
Finished goods	53.2	46.3
Operating and other supplies	252.3	225.3
Total inventories	$ 467.5	$ 477

Debt - Activity (Details)

Debt - Activity (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023	Apr. 30, 2021
Debt Instrument [Line Items]
Total debt	$ 480.4	$ 479.2
Industrial revenue bonds, variable
Debt Instrument [Line Items]
Maximum variable interest rate	12%
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly	$ 7.8	7.8
Effective interest rate	4.14%
Revolving credit facility | U.S. revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility	$ 0	23.7
Effective interest rate	9.25%
Revolving credit facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 0	0
Effective interest rate	8.84%
Casthouse Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 11.3	5.5
Financing fees	0
Secured debt	$ 118.7	98.8
Stated interest rate, percentage	8.88%
Iceland Term Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 0	1.3
Stated interest rate, percentage	3.20%
Vlissingen facility agreement | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 10	10
Secured debt	$ 10
Stated interest rate, percentage	8.75%
Senior secured notes, 7.5% | Senior notes
Debt Instrument [Line Items]
Financing fees	$ 2.3
Stated interest rate, percentage	7.50%		7.50%
7.5% senior secured notes due April 1, 2028, net of financing fees of $2.3 million at June 30, 2024, interest payable semiannually	$ 247.7	247.4
Senior convertible notes, 2.75% | Senior notes
Debt Instrument [Line Items]
Financing fees	$ 1.3
Stated interest rate, percentage	2.75%		2.75%
2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.3 million at June 30, 2024, interest payable semiannually	$ 84.9	$ 84.7

Debt - Narrative (Details)

Debt - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Apr. 30, 2021 USD ($) $ / shares	Jun. 30, 2024 USD ($)	Sep. 28, 2022 USD ($)	Nov. 30, 2013 USD ($)
Senior secured notes, 7.5% | Senior notes
Line of Credit Facility [Line Items]
Stated interest rate, percentage	7.50%	7.50%
Face amount	$ 250
Proceeds from issuance of Senior Notes due 2028	$ 245.2
Senior secured notes, 7.5% | Senior notes | Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument		$ 252.6
Senior convertible notes, 2.75% | Senior notes
Line of Credit Facility [Line Items]
Stated interest rate, percentage	2.75%	2.75%
Face amount	$ 86.3
Percentage of principal amount redeemed	100%
Proceeds from issuance of Convertible Senior Notes	$ 83.7
Conversion ratio	0.0533547
Conversion price (in dollars per share) | $ / shares	$ 18.74
Senior convertible notes, 2.75% | Senior notes | Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument		$ 94.7
U.S. revolving credit facility | Iceland revolving line of credit
Line of Credit Facility [Line Items]
Credit facility maximum amount		$ 100	$ 100	$ 50

Debt - Credit Facility Narrativ

Debt - Credit Facility Narrative (Details) - Revolving credit facility - USD ($) $ in Millions	Jun. 30, 2024	Sep. 28, 2022	Jun. 14, 2022	Feb. 04, 2022	Nov. 30, 2013
U.S. revolving credit facility
Line of Credit Facility [Line Items]
Credit facility maximum amount			$ 250
Outstanding borrowings	$ 0
Outstanding letters of credit issued	40.8
Credit facility maximum amount	250
Letter of credit
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount	150
Iceland revolving line of credit
Line of Credit Facility [Line Items]
Credit facility maximum amount	100	$ 100			$ 50
Outstanding borrowings	0
Outstanding letters of credit issued	$ 0
Credit facility maximum amount				$ 80

Debt - U.S. Credit Facility Sch

Debt - U.S. Credit Facility Schedule (Details) - U.S. revolving credit facility - Revolving credit facility $ in Millions	Jun. 30, 2024 USD ($)
Line of Credit Facility [Line Items]
Credit facility maximum amount	$ 250
Borrowing availability	162.1
Outstanding letters of credit issued	40.8
Outstanding borrowings	0
Borrowing availability, net of borrowings	$ 121.3

Debt - Iceland Credit Facility

Debt - Iceland Credit Facility Schedule (Details) - Iceland revolving line of credit - Revolving credit facility - USD ($) $ in Millions	Jun. 30, 2024	Sep. 28, 2022	Nov. 30, 2013
Line of Credit Facility [Line Items]
Credit facility maximum amount	$ 100	$ 100	$ 50
Borrowing availability	100
Outstanding letters of credit issued	0
Outstanding borrowings	0
Borrowing availability, net of borrowings	$ 100

Debt - Casthouse Facility Narra

Debt - Casthouse Facility Narrative (Details) € in Millions, $ in Millions	Nov. 02, 2021 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 09, 2022 USD ($)	Sep. 30, 2022 EUR (€)
Casthouse Facility
Debt Instrument [Line Items]
Debt instrument, term	8 years
Credit facility maximum amount	$ 130
Debt instrument, quarterly installment fee	1.739%
Debt instrument, remaining payment after drawdown of funds	60%
Medium-term notes, outstanding borrowings		$ 130
Casthouse Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Stated interest rate, percentage		8.88%
Secured debt		$ 118.7	$ 98.8
Medium-term Notes
Debt Instrument [Line Items]
Credit facility maximum amount | €					€ 13.6
Iceland Term Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Stated interest rate, percentage		3.20%
Vlissingen facility agreement | Iceland revolving line of credit
Debt Instrument [Line Items]
Stated interest rate, percentage		8.75%
Face amount				$ 90
Secured debt		$ 10
Industrial revenue bonds, variable
Debt Instrument [Line Items]
Maximum variable interest rate		12%
Surety Bond
Debt Instrument [Line Items]
Loss contingency accrual		$ 6.6

Commitments and Contingencies (

Commitments and Contingencies (Details)		1 Months Ended		6 Months Ended	12 Months Ended
	Aug. 18, 2017 USD ($)	Oct. 31, 2021 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2024 USD ($) laborUnion MW	Dec. 31, 2013 USD ($)	Jun. 30, 2023 USD ($)
Labor Commitments [Abstract]
Percentage of total work force in union				59%
Percentage of Grundartangi work force represented by the labor unions				87%
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				38%
Percentage of foreign work force, represented by the union				61%
Contingent consideration, accrued interest and principal				$ 31,600,000
Netherlands
Labor Commitments [Abstract]
Percentage of total work force in union				100%
PBGC
PBGC Settlement [Abstract]
Required pension contributions above minimum					$ 17,400,000
Pension contributions, amended term, annual contribution		$ 2,400,000
Pension contributions, amended term, total contribution		$ 9,600,000		$ 6,900,000		$ 2,400,000
Pension contributions, term		4 years
Payment for pension benefits				$ 0
Kenergy | Century Marketer, LLC
Power Contingencies [Abstract]
Extension term				1 year
Required termination period				1 year
Hawesville | Kenergy
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%
Grundartangi - HS, Landsvirkjun and OR
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
Power currently available under the power purchase agreement, requested (in megawatts) | MW				182
Ravenswood Retiree Medical Benefits Changes
Ravenswood litigation [Abstract]
Litigation settlement amount	$ 23,000,000
Ravenswood litigation settlement installment period	10 years
Litigation payment to trust			$ 5,000,000
Gain (loss) related to litigation settlement			5,500,000
Loss contingency accrual			$ 12,500,000
Litigation settlement, annual installment				$ 2,000,000
Litigation settlement installment period				9 years
Other current liabilities				$ 2,000,000
Other Liabilities				$ 3,500,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss ("AOCL") - Components of AOCL (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	$ (100.4)		$ (100.4)		$ (100.2)
Defined benefit plan liabilities	2.3		2.3		2.3
Accumulated other comprehensive loss	(98.1)		(98.1)		(97.9)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			355.6
Net amount reclassified to net income (loss)	1.5	$ 2.2	3.2	$ 3.3
Other comprehensive loss before reclassifications			(3.4)
Ending balance	601.5		601.5
Defined benefit plan liabilities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	(101.8)		(101.8)		(101.8)
Defined benefit plan liabilities	2.6		2.6		2.6
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(101)	(94.4)	(99.4)	(95.6)
Net amount reclassified to net income (loss)	1.5	2.2	3.3	3.4
Other comprehensive loss before reclassifications			(3.4)
Ending balance	(99.5)	(92.2)	(99.5)	(92.2)
Unrealized gain on financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	1.4		1.4		1.6
Defined benefit plan liabilities	(0.3)		(0.3)		$ (0.3)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.4	1.5	1.5	1.6
Net amount reclassified to net income (loss)	0	0	(0.1)	(0.1)
Other comprehensive loss before reclassifications			0
Ending balance	1.4	1.5	1.4	1.5
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(99.6)	(92.9)	(97.9)	(94)
Ending balance	$ (98.1)	$ (90.7)	$ (98.1)	$ (90.7)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss ("AOCL") - Reclassifications out of AOCL (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	$ (540.4)	$ (559.6)	$ (1,013.4)	$ (1,063.9)
Selling, general and administrative expenses	(12.3)	(12)	(26.4)	(25.4)
Other operating expense - net	(1.7)	(4.6)	(2.2)	(11.8)
Income tax effect	(0.5)	10	(1)	10.2
Net of tax	(2.5)	7.5	244.3	(31.1)
Reclassification out of accumulated other comprehensive income | Defined benefit plan and other postretirement liabilities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	0.7	1.4	1.6	2.2
Selling, general and administrative expenses	0.1	0.1	0.3	0.3
Other operating expense - net	0.7	0.7	1.4	0.9
Income tax effect	0	0	0	0
Net of tax	1.5	2.2	3.3	3.4
Reclassification out of accumulated other comprehensive income | Unrealized gain (loss) on financial instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	0	0	(0.1)	(0.1)
Income tax effect	0	0	0	0
Net of tax	$ 0	$ 0	$ (0.1)	$ (0.1)

Components of Net Periodic Be_3

Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0.7	$ 0.1	$ 1.3	$ 1.1
Interest cost	3.2	4.4	6.7	7
Expected return on plan assets	(4.1)	(1.7)	(7.9)	(7.5)
Amortization of prior service costs	0	0	0.1	0.1
Amortization of net loss	1.3	2.4	3	3.2
Net periodic benefit cost (income)	1.1	5.2	3.2	3.9
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.1	0	0.1	0.1
Interest cost	0.9	1.2	1.9	1.9
Amortization of prior service costs	(0.1)	0	(0.1)	0
Amortization of net loss	0.3	(0.2)	0.3	0.1
Net periodic benefit cost (income)	$ 1.2	$ 1	$ 2.2	$ 2.1

Derivatives - Narrative (Detail

Derivatives - Narrative (Details)	6 Months Ended
	Jun. 30, 2024 DKK (kr) MWh MMBTU Boe t	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Derivative [Line Items]
Restricted cash | $		$ 0	$ 0
LME forward financial sales contracts
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	42,654
MWP Forward Financial Sales Contracts
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	25,200
Fixed For Floating Swaps
Derivative [Line Items]
Open position to offset fixed prices (in tonnes)	0
USD ISK Forward Swap
Derivative [Line Items]
Derivative, forward contracts | kr	kr 0
Henry Hub Natural Gas Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) | MMBTU	0
HFO Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) | Boe	240,000
Indiana Hub Power Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) | MWh	460,080

Derivatives - Assets and Liabil

Derivatives - Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Related Party
Derivative [Line Items]
Due to affiliate, current	$ 108.3	$ 101.4
Commodity contracts | Related Party
Derivative [Line Items]
Due to affiliate, current	4	6.4
Not designated as hedging instrument
Derivative [Line Items]
Derivative liability	6.7	7.9
Not designated as hedging instrument | Commodity contracts
Derivative [Line Items]
Derivative asset	5.5	2.9
Derivative liability	6.7	7.8
Not designated as hedging instrument | Foreign exchange contracts
Derivative [Line Items]
Derivative liability	$ 0	$ 0.1

Derivatives - Net Gain (Loss) (

Derivatives - Net Gain (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Derivative [Line Items]
Derivative gain (loss) on derivative, net	$ (4)	$ 9.1	$ 3.4	$ (48.5)
Commodity contracts
Derivative [Line Items]
Derivative gain (loss) on derivative, net	(4)	9.1	3.5	(50.1)
Commodity contracts | Related Party | Glencore
Derivative [Line Items]
Derivative gain (loss) on derivative, net	(1.9)	11.4	2.5	(3.5)
Foreign exchange contracts
Derivative [Line Items]
Derivative gain (loss) on derivative, net	$ 0	$ 0	$ (0.1)	$ 1.6