Century Aluminum (CENX) 10-Q 9 Aug 23 2023 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Jun. 30, 2023	Aug. 08, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2023
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 Common Stock, Shares Outstanding (in shares)		92,384,873
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 Central Index Key	0000949157
Amendment Flag	false
Document Fiscal Year Focus	2023
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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
NET SALES:
Total net sales	$ 575.5	$ 856.6	$ 1,127.9	$ 1,610.2
Cost of goods sold	559.6	840.7	1,063.9	1,501.1
Gross profit	15.9	15.9	64	109.1
Selling, general and administrative expenses	12	5.8	25.4	17.5
Asset impairment	0	159.4	0	159.4
Other operating expense - net	4.6	0.2	11.8	0.4
Operating (loss) income	(0.7)	(149.5)	26.8	(68.2)
Interest expense	(8.7)	(5.7)	(17.4)	(13)
Interest income	0.4	0	0.7	0.1
Net gain (loss) on forward and derivative contracts	9.1	231.8	(48.5)	175.1
Other (expense) income - net	(3.5)	3.1	(3.8)	5.1
(Loss) income before income taxes	(3.4)	79.7	(42.2)	99.1
Income tax benefit (expense)	10	(42.3)	10.2	(44)
Income (loss) before equity in earnings of joint ventures	6.6	37.4	(32)	55.1
Equity in (losses) earnings of joint ventures	0	0	0	0
Net income (loss)	6.6	37.4	(32)	55.1
Net loss attributable to noncontrolling interests	(0.9)	0	(0.9)	0
Net income (loss) attributable to Century stockholders	7.5	37.4	(31.1)	55.1
Less: net income allocated to participating securities	0.4	2.3	0	3.3
Net income (loss) allocated to common stockholders	$ 7.1	$ 35.1	$ (31.1)	$ 51.8
INCOME (LOSS) ATTRIBUTABLE TO CENTURY STOCKHOLDERS PER COMMON SHARE:
Basic (in dollars per share)	$ 0.08	$ 0.38	$ (0.34)	$ 0.57
Diluted (in dollars per share)	$ 0.07	$ 0.36	$ (0.34)	$ 0.54
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	92.3	91.2	92.3	91.2
Diluted (in shares)	93.2	97.6	92.3	97.9
Related Party
NET SALES:
Total net sales	$ 427.2	$ 483.5	$ 839.4	$ 916.6
Nonrelated Party
NET SALES:
Total net sales	$ 148.3	$ 373.1	$ 288.5	$ 693.6

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Comprehensive income (loss):
Net income (loss)	$ 6.6	$ 37.4	$ (32)	$ 55.1
Other comprehensive income before income tax effect:
Net (loss) income on foreign currency cash flow hedges reclassified as income	0	(0.1)	(0.1)	(0.1)
Defined benefit plans and other postretirement benefits:
Amortization of prior service benefit (cost) during the period	0.1	(0.5)	0.1	(0.9)
Amortization of net gain during the period	2.1	1.4	3.3	2.5
Other comprehensive income before income tax effect	2.2	0.8	3.3	1.5
Income tax effect	0	0	0	(0.1)
Other comprehensive income	2.2	0.8	3.3	1.4
Comprehensive income (loss)	8.8	38.2	(28.7)	56.5
Comprehensive loss attributable to noncontrolling interests	(0.9)	0	(0.9)	0
Comprehensive income (loss) attributable to Century stockholders	$ 9.7	$ 38.2	$ (27.8)	$ 56.5

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
ASSETS
Cash and cash equivalents	$ 50.6	$ 54.3
Restricted cash	10.9	1.2
Accounts receivable - net	48.8	66.9
Inventories	510.8	398.8
Derivative assets	34.5	127.3
Prepaid and other current assets	26.2	24.5
Total current assets	700	677.8
Property, plant and equipment - net	860.8	744.4
Deferred tax assets	110.8	0.2
Other assets	75.7	49.6
TOTAL	1,747.3	1,472
LIABILITIES:
Accounts payable, trade	191.2	167.3
Accrued compensation and benefits	42.3	33
Accrued and other current liabilities	66.6	37.6
Derivative liabilities	3.6	9.7
Deferred credit - preliminary bargain purchase gain	103.3	0
U.S. revolving credit facility	63.2	90
Iceland revolving credit facility	73	35
Industrial revenue bonds	7.8	7.8
Total current liabilities	573.4	410.7
Senior notes payable	247	246.6
Convertible senior notes payable	84.5	84.4
Grundartangi casthouse debt facility	69.3	49.4
Iceland term facility, net of current portion	0	1.2
Accrued benefits - less current portion	116.8	118
Other liabilities	11.1	10.5
Leases - right of use liabilities	21.8	20.9
Deferred tax liabilities	93	103.1
Asset retirement obligations	124.1	19.6
Total noncurrent liabilities	769.1	662
COMMITMENTS AND CONTINGENCIES (NOTE 12)
SHAREHOLDERS’ EQUITY:
Preferred stock (Note 8)	0	0
Common stock (Note 8)	1	1
Additional paid-in capital	2,541	2,539.6
Treasury stock, at cost	(86.3)	(86.3)
Accumulated other comprehensive loss	(90.7)	(94)
Accumulated deficit	(1,992.1)	(1,961)
Total Century shareholders’ equity	372.9	399.3
Noncontrolling interest	31.9	0
Total equity	404.8	399.3
TOTAL	1,747.3	1,472
Related Party
ASSETS
Due from affiliates	18.2	4.8
LIABILITIES:
Due to affiliates	13.8	17
Iceland Term Facility	8.6	13.3
Due to affiliates - less current portion	$ 1.5	$ 8.3

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss) income	$ (32)	$ 55.1
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Unrealized loss (gain) on derivative instruments	66.3	(217.5)
Lower of cost or NRV inventory adjustment	0	52.8
Depreciation and amortization	31.5	42.1
Deferred tax (benefit) provision	(12.6)	41.9
Asset impairment	0	159.4
Other non-cash items - net	3.7	(9)
Change in operating assets and liabilities, net of acquisition:
Accounts receivable - net	26	(41.6)
Due from affiliates	(12.2)	(8.7)
Inventories	(18.5)	(43)
Prepaid and other current assets	7.7	1.1
Accounts payable, trade	(72.9)	47.5
Due to affiliates	7.7	(28.8)
Accrued and other current liabilities	3	16.6
Other - net	0.4	0.7
Net cash (used in) provided by operating activities	(1.9)	68.6
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(36.6)	(51.8)
Proceeds from sales of property, plant and equipment	0	0.1
Acquisition of subsidiary net of cash acquired	19.4	0
Net cash used in investing activities	(17.2)	(51.7)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under revolving credit facilities	407.8	596.4
Repayments under revolving credit facilities	(396.6)	(660)
Debt issuance costs	0	(1.5)
Repayment of Iceland Term Facility	(6.1)	0
Borrowings under Grundartangi casthouse debt facility	20	40
Net cash provided by (used in) financing activities	25.1	(25.1)
CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	6	(8.2)
Cash, cash equivalents and restricted cash, beginning of period	55.5	40.7
Cash, cash equivalents and restricted cash, end of period	61.5	32.5
Cash paid for:
Interest	17.9	13.1
Taxes, net of refunds	(0.3)	1.2
Non-cash investing activities:
Capital expenditures	7.8	2.6
Capitalized interest	$ 2.3	$ 2.9

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, 2021			58,542
Beginning balance at Dec. 31, 2021	$ 421	$ 421	$ 0	$ 1	$ 2,535.5	$ (86.3)	$ (82.3)	$ (1,946.9)	$ 0
Beginning balance (in shares) at Dec. 31, 2021				91,231,611
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	55.1	55.1						55.1
Other comprehensive income	1.4	1.4					1.4
Share-based compensation (in shares)				22,128
Share-based compensation	1.5	1.5			1.5
Conversion of preferred stock to common stock (in shares)			(166)	16,635
Ending balance (in shares) at Jun. 30, 2022			58,376
Ending balance at Jun. 30, 2022	479	479	$ 0	$ 1	2,537	(86.3)	(80.9)	(1,891.8)	0
Ending balance (in shares) at Jun. 30, 2022				91,270,374
Beginning balance (in shares) at Mar. 31, 2022			58,542
Beginning balance at Mar. 31, 2022	439.8	439.8	$ 0	$ 1	2,536	(86.3)	(81.7)	(1,929.2)	0
Beginning balance (in shares) at Mar. 31, 2022				91,231,611
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	37.4	37.4						37.4
Other comprehensive income	0.8	0.8					0.8
Share-based compensation (in shares)				22,128
Share-based compensation	1	1			1
Conversion of preferred stock to common stock (in shares)			(166)	16,635
Ending balance (in shares) at Jun. 30, 2022			58,376
Ending balance at Jun. 30, 2022	479	479	$ 0	$ 1	2,537	(86.3)	(80.9)	(1,891.8)	0
Ending balance (in shares) at Jun. 30, 2022				91,270,374
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			92,323,978
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (32)	(31.1)						(31.1)	(0.9)
Other comprehensive 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 of business acquired	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			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 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 of business acquired	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			92,358,549

General

General	6 Months Ended
	Jun. 30, 2023
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, 2022. 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 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. 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, an unincorporated joint venture between the Company and Clarendon Alumina Production Limited. Clarendon Alumina Production's interest in the joint venture is reflected as noncontrolling interest on the accompanying Consolidated Balance Sheet.

Acquisition of Jamalco

Acquisition of Jamalco	6 Months Ended
	Jun. 30, 2023
Business Combination and Asset Acquisition [Abstract]
Acquisition of Jamalco	Acquisition of Jamalco On May 2, 2023, our wholly-owned subsidiary, Century Aluminum Jamaica Holdings, Inc. ("Century Jamaica"), completed the acquisition of all the outstanding share capital of General Alumina Holdings Limited, the holder of a 55% interest in Jamalco JV ("Jamalco"), an unincorporated joint venture engaged in bauxite mining and alumina production in Jamaica. The remaining 45% interest in Jamalco is owned by Clarendon Alumina Production Limited ("CAP"), which in turn is owned by the Government of Jamaica. Total consideration for the acquisition was approximately $8.3 million in cash, comprised of a purchase price of $1.00 and $8.3 million related to the remaining restricted cash as of the completion date. The acquisition is expected to result in a bargain purchase gain in part due to the seller experiencing financial distress following curtailment of Jamalco's operations in the second half of 2021 due to a facility fire, with operations restarting in the second half of 2022. The acquisition was accounted for as a business combination under the acquisition method of accounting. Determining the fair value of identified assets acquired, liabilities assumed and noncontrolling interest requires judgment and involves the use of significant estimates and assumptions. The Company based its fair value estimates on assumptions it believes to be reasonable but are inherently uncertain. These estimates and valuation of the property, plant and equipment, current assets, current liabilities, other long-term assets, deferred tax assets, including the realizability of deferred tax assets, and asset retirement obligations acquired as well as the related deferred credit and noncontrolling interest are preliminary as of June 30, 2023 and are subject to change as we finalize the valuation or if additional information about the facts and circumstances that existed at the acquisition date become available. We expect to finalize the purchase price allocation as soon as practicable within the measurement period, but not later than one year following the acquisition date. The following table summarizes the consideration transferred and the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition: Preliminary purchase price allocation Amount Consideration transferred Cash paid $ 8.3 Total consideration transferred $ 8.3 Less: identifiable assets acquired and liabilities assumed Cash and cash equivalents $ 19.4 Restricted cash 8.3 Inventories 93.4 Accounts receivable - net 8.0 Prepaid and other current assets 7.7 Property, plant and equipment - net 102.2 Deferred tax assets 108.1 Other long-term assets 25.5 Accounts payable, trade (92.9) Accrued and other current liabilities (33.9) Asset retirement obligations (101.4) Total identifiable net assets acquired 144.4 Less: noncontrolling interest (32.8) Deferred credit - preliminary bargain purchase gain (103.3) Fair value allocated to net assets acquired, net of bargain purchase gain $ 8.3 For the three and six months ended June 30, 2023, Jamalco contributed $43.7 million to our total revenues. In connection with the acquisition, the Company incurred approximately $0.7 million and $1.6 million of transaction costs, respectively, for the three and six months ended June 30, 2023 which are included in selling, general and administrative expenses on the Consolidated Statements of Operations. The following unaudited pro forma financial information reflects the results of operations of the Company for the three and six months ended June 30, 2023 and 2022, respectively, as if the acquisition of Jamalco had been completed on January 1, 2022. This unaudited pro forma financial information has been prepared for informational purposes and is not necessarily indicative of the actual consolidated results of operations had the acquisition been completed on January 1, 2022, nor is the information indicative of future results of operations of the combined companies. Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Revenue $ 595.3 $ 856.6 $ 1,177.6 $ 1,610.2 Earnings $ 6.7 $ 36.1 $ (33.0) $ 62.4

Curtailment of Operations - Haw

Curtailment of Operations - Hawesville	6 Months Ended
	Jun. 30, 2023
Restructuring and Related Activities [Abstract]
Curtailment of Operations - Hawesville	Curtailment of Operations - HawesvilleIn 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.For the three and six months ended June 30, 2023, we incurred curtailment charges of approximately $4.4 million and $11.4 million, including $3.6 million and $9.0 million related to excess capacity charges, respectively. These charges were partially offset by income related to scrap and materials sales of $0.5 million and $1.2 million for the three and six months ended June 30, 2023. Comparatively, for the three and six months ended June 30, 2022 we recognized $8.2 million of expenses related to accrued wages and severance, triggered by our issuance of the WARN notice.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The significant related party transactions occurring during the six months ended June 30, 2023 and 2022 are described below. We believe all of our transactions with related parties are at prices that approximate market. Glencore Ownership As of June 30, 2023 , Glencore plc and its affiliates (together "Glencore") beneficially owned 42.9% of Century’s outstanding common stock (46.1% o n 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, 2023 and 2022, we derived approximately 74% and 57% 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, 2023, we recorded $65.8 million and $86.8 million of revenue related to alumina sales to Glencore, respectively. For the three and six months ended June 30, 2022, we recorded $13.9 million 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 months ended 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. 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 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. Summary A summary of the aforementioned significant related party sales and purchases is as follows: Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Net sales to Glencore $ 427.2 $ 483.5 $ 839.4 $ 916.6 Purchases from Glencore (1) 75.2 172.8 151.4 227.3 (1) Includes settlements of financial contract positions.

Revenue

Revenue	6 Months Ended
	Jun. 30, 2023
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, 2023 2022 2023 2022 United States $ 319.5 $ 583.4 $ 661.8 $ 1,089.5 Iceland 212.3 273.2 422.4 520.7 Jamaica 43.7 — 43.7 — Total $ 575.5 $ 856.6 $ 1,127.9 $ 1,610.2

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2023
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, 2023 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 5.8 $ — $ — $ 5.8 Trust assets (1) 1.1 — — 1.1 Derivative instruments — 37.9 — 37.9 TOTAL $ 6.9 $ 37.9 $ — $ 44.8 LIABILITIES: Derivative instruments — (6.1) — (6.1) TOTAL $ — $ (6.1) $ — $ (6.1) Recurring Fair Value Measurements As of December 31, 2022 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 5.6 $ — $ — $ 5.6 Trust assets (1) 0.1 — — 0.1 Derivative instruments — 127.3 1.8 129.1 TOTAL $ 5.7 $ 127.3 $ 1.8 $ 134.8 LIABILITIES: Derivative instruments — 26.4 4.6 31.0 TOTAL $ — $ 26.4 $ 4.6 $ 31.0 (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 or Level 3 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 Nord Pool power price swaps Discounted cash flows Quoted Nord Pool forward market Indiana Hub power price swaps Discounted cash flows Quoted Indiana Hub forward market FX swaps Discounted cash flows Euro/USD forward exchange rate Casthouse currency hedges Discounted cash flows Euro/USD forward exchange rate; ISK/USD forward exchange rate NYMEX Henry Hub natural gas price swaps Discounted cash flows Quoted NYMEX Henry Hub 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 inputs for recurring fair value measurements categorized within Level 3 of the fair value hierarchy, along with information regarding significant unobservable inputs used to value Level 3 assets and liabilities: Recurring Level 3 Fair Value Measurements: As of June 30, 2023 As of December 31, 2022 Asset / Liability Valuation Technique Observable Inputs Significant Unobservable Input Fair Value Value/Range of Unobservable Input Fair Value Value/Range of Unobservable Input LME forward financial sales contracts Discounted cash flows Quoted LME forward market Discount rate net (1) $ — 8.58% $ (2.8) 8.58% (1) Represents risk adjusted discount rate. 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 months ended June 30, 2023. Level 3 Assets Level 3 Liabilities For the three months ended June 30, 2022 LME Forward financial sales contracts LME forward financial sales contracts Casthouse currency hedges Balance as of April 1, 2022 $ — $ (16.7) $ — Total realized/unrealized gains (losses) Included in net income (1) — 12.9 — Transfers into Level 3 (2) 1.6 — 0.0 Balance as of June 30, 2022 $ 1.6 $ (3.8) $ 0.0 Change in unrealized gains (losses) (1) $ — $ 12.9 $ 0.0 (1) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts." (2) Transfers into Level 3 due to period of time remaining in derivative contract. For the six months ended June 30, 2023 Level 3 Assets Level 3 Liabilities 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) Transfers 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." Level 3 Assets Level 3 Liabilities For the six months ended June 30, 2022 LME forward financial sales contracts Nord Pool Swaps LME forward financial sales contracts FX Swaps Casthouse currency hedges Balance as of January 1, 2022 $ — $ 0.2 $ (5.1) $ (0.2) $ — Total realized/unrealized loss Included in net income (1) $ — $ — $ 3.8 $ — $ — Transfers into Level 3 (2) $ 1.6 $ — $ (2.5) $ — $ — Transfers out of Level 3 (3) $ — $ (0.2) $ — $ 0.2 $ — Balance as of June 30, 2022 $ 1.6 $ — $ (3.8) $ — $ — Change in unrealized gains (losses) (1) $ — $ — $ 3.8 $ — $ — ( 1) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts." (2) Transfers into Level 3 due to contracts with applied discount rate entered into during the six months ended June 30, 2022. (3) Transfers out of Level 3 due to period of time remaining in derivative contract.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2023
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share ("EPS") amounts are 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. The following table shows the basic and diluted (loss) earnings per share: For the three months ended June 30, 2023 2022 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net income attributable to Century stockholders $ 7.5 $ 37.4 Less: net income allocated to participating securities 0.4 2.3 Basic EPS: Net income allocated to common stockholders $ 7.1 92.3 $ 0.08 $ 35.1 91.2 $ 0.38 Effect of Dilutive Securities (1) : Share-based compensation (0.2) 0.9 (0.3) 1.6 Convertible senior notes — — 0.7 4.8 Diluted EPS: Net income allocated to common stockholders with assumed conversion $ 6.9 93.2 $ 0.07 $ 35.5 97.6 $ 0.36 For the six months ended June 30, 2023 2022 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net (loss) income attributable to Century stockholders $ (31.1) $ 55.1 Less: net income allocated to participating securities — 3.3 Basic EPS: Net (loss) income allocated to common stockholders $ (31.1) 92.3 $ (0.34) $ 51.8 91.2 $ 0.57 Effect of Dilutive Securities (1) : Share-based compensation — — (0.5) 1.9 Convertible senior notes — — 1.4 4.8 Diluted EPS: Net (loss) income allocated to common stockholders with assumed conversion $ (31.1) 92.3 $ (0.34) $ 52.7 97.9 $ 0.54 Three months ended June 30, Six months ended June 30, Securities excluded from the calculation of diluted EPS (in millions) (1) : 2023 2022 2023 2022 Share-based compensation — — 0.9 — Convertible preferred shares 5.4 5.9 5.4 5.9 Convertible notes 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, 2023
Stockholders' Equity Note [Abstract]
Shareholders’ Equity	Shareholders’ Equity Common Stock As of June 30, 2023 and December 31, 2022, we had 195,000,000 shares of common stock, $0.01 cent par value per share, authorized under our Restated Certificate of Incorporation, of which 99,545,070 shares were issued and 92,358,549 shares were outstanding at June 30, 2023, and 99,510,499 were issued and 92,323,978 shares were outstanding at December 31, 2022. 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, 2023 and December 31, 2022, we had 5,000,000 shares of preferred stock, $0.01 cent par value per share, authorized under our Restated Certificate of Incorporation. Our Board of Directors may issue preferred stock in one or more series and determine for each series the dividend rights, conversion rights, voting rights, redemption rights, 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. Glencore holds all of the issued and outstanding Series A Convertible Preferred Stock. At June 30, 2023 and December 31, 2022, 53,706 and 53,854 shares of Series A Convertible Preferred Stock were outstanding, respectively. 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

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the three months ended June 30, 2023 and June 30, 2022, we recorded an income tax benefit of $10.0 million and an income tax expense of $42.3 million, respectively. For the six months ended June 30, 2023 and June 30, 2022, we recorded an income tax benefit of $10.2 million and an income tax expense of $44.0 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 normally determined using an estimate of our annual effective tax rate, adjusted for discrete items. In the second quarter of 2023, we determined that we could not make a reliable estimate of the annual effective tax rate primarily due to the sensitivity of the estimated annual tax rate to changes in forecasted pre-tax earnings. As a result, the effective tax rate for the six months ended June 30, 2023 was calculated based on 2023 year-to-date results. 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, 2023, 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. The Inflation Reduction Act of 2022 ("IRA") was signed into law on August 16, 2022, and the CHIPS and Science Act of 2022 was signed into law on August 9, 2022. These laws, effective January 1, 2023, implement new tax provisions, primarily a 15% corporate alternative minimum tax and a nondeductible 1% excise tax on the fair market value of stock repurchased by publicly traded corporations. As of June 30, 2023, these provisions, which were effective January 1, 2023, have not had any material impact on the financial statements. The IRA provides several tax incentives to promote clean energy and the production of critical minerals in the U.S. We are continuing to evaluate potential tax benefits available under the acts as additional guidance is issued.

Inventories

Inventories	6 Months Ended
	Jun. 30, 2023
Inventory, Net [Abstract]
Inventories	Inventories Inventories consist of the following: June 30, 2023 December 31, 2022 Raw materials $ 117.6 $ 64.9 Work-in-process 86.4 46.0 Finished goods 44.4 58.0 Operating and other supplies 262.4 229.9 Total inventories $ 510.8 $ 398.8 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, 2023
Debt Disclosure [Abstract]
Debt	Debt June 30, 2023 December 31, 2022 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) 63.2 90.0 Iceland Revolving Credit Facility (3) 73.0 35.0 Iceland Term Facility (4) 8.6 13.3 Debt classified as non-current liabilities: Grundartangi casthouse facility, net of financing fees of $0.7 million at June 30, 2023 (5) 69.3 49.4 Iceland Term Facility, net of financing fees of $0.0 million and current portion at June 30, 2023 (4) — 1.2 7.5% senior secured notes due April 1, 2028, net of financing fees of $3.0 million at June 30, 2023, interest payable semiannually 247.0 246.6 2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.7 million at June 30, 2023, interest payable semiannually 84.5 84.4 Total $ 553.4 $ 527.7 (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, 2023 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, 2023 was 9.00%. (3) We incur interest at base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2023 wa s 8.16%. (4) We incur interest at a rate equal to 3.2% plus EUR EURIBOR 1 month as published by the European Money Market Institute as defined within the agreement. The interest rate at June 30, 2023 was 6.46%. (5) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2023 was 8.63%. 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. As of June 30, 2023, the total estimated fair value of the 2028 Notes was $237.6 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. 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, 2023, 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, 2023, the if-converted value of the Convertible Notes does not exceed the outstanding principal amount. As of June 30, 2023, the total estimated fair value of the Convertible Notes was $66.6 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. 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. 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, 2023, there were $63.2 million in outstanding borrowings and $33.3 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, 2023 Credit facility maximum amount 250.0 Borrowing availability 160.0 Outstanding letters of credit issued 33.3 Outstanding borrowings 63.2 Borrowing availability, net of outstanding letters of credit and borrowings 63.5 Iceland Revolving Credit Facility Our wholly-owned subsidiary, Nordural Grundartangi ehf ("Grundartangi"), entered into a $80.0 million revolving credit facility agreement with Landsbankinn hf., dated November 2013, as amended (the "Iceland revolving credit facility"). 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, 2023, there were $73.0 million in outstanding borrowings under our Iceland revolving credit facility. The Iceland revolving credit facility has a term through November 2024. Status of our Iceland revolving credit facility: June 30, 2023 Credit facility maximum amount 100.0 Borrowing availability 100.0 Outstanding letters of credit issued — Outstanding borrowings 73.0 Borrowing availability, net of borrowings 27.0 Grundartangi Casthouse Facility Our wholly-owned subsidiary, Grundartangi, has entered into an eight-year Term Facility Agreement with Arion Bank hf, dated November 2021, as amended (the "Casthouse Facility") to provide for borrowings up to $130.0 million associated with construction of the new billet casthouse at Grundartangi (the"casthouse project"). 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, 2023, there were $70.0 million in outstanding borrowings under the Casthouse Facility. 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 are made in equal monthly installments, the first payment occurring in February 2023, with the remainder of the principal amount to be paid no later than the termination date in January 2024. Borrowings under the Iceland Term Facility bear interest at a rate equal to 3.2% plus EUR EURIBOR 1 month as published at any time by the European Money Markets Institute. As of June 30, 2023, there were €8.0 million ( $8.6 million, based on the prevailing exchange rate on June 30, 2023) in outstanding borrowings under the Iceland Term Facility. 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 payable on December 2, 2024, the maturity date of the Vlissingen Facility Agreement. As of June 30, 2023, there were no outstanding borrowings under the Vlissingen Facility Agreement. 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, 2023, 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, 2023
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, 2023, $2.0 million was recorded in other current liabilities and $5.0 million was recorded in other liabilities. 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 d id not make any contributions for the three month periods ended June 30, 2023, or 2022. 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, 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 EDF Trading North America, LLC (“EDF") which provides market-based power to the Hawesville smelter. Under this arrangement, the power companies purchase power on the open market and pass it through to Hawesville at Midcontinent Independent System Operator ("MISO") pricing plus transmission and other costs. The power supply arrangement with Kenergy has an effective term through December 2023. The arrangement with EDF to act as our market participant with MISO to purchase power from MISO for resale to Kenergy, which then resells the power to Hawesville, terminated May 31, 2023. Effective June 1, 2023, Century currently acts as its own MISO market participant (through an indirect, wholly-owned subsidiary). Sebree Sebree has a power supply arrangement with Kenergy and EDF which provides market-based power to the Sebree smelter. Similar to the arrangement at Hawesville, the power companies purchase power on the open market and pass it through to Sebree at MISO pricing plus transmission and other costs. The power supply arrangement with Kenergy has an effective term through December 2023. The arrangement with EDF to act as our market participant with MISO to purchase power from MISO for resale to Kenergy, which then resells the power to Sebree, terminated May 31, 2023. Effective June 1, 2023, Century currently acts as its own MISO market participant (through an indirect, wholly-owned subsidiary). Mt. Holly Century Aluminum of South Carolina, Inc. has a power supply agreement with Santee Cooper that has an effective term from April 1, 2021 through December 2023. 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. The contract provides sufficient energy to allow Mt. Holly to produce at 75% of full production capacity. Grundartangi Grundartangi has power purchase agreements for approximately 545 MW with HS Orka hf ("HS"), Landsvirkjun and Orkuveita Reykjavikur ("OR") to provide power to its Grundartangi smelter. These power purchase agreements expire on various dates from 2026 through 2036 (subject to extension). The power purchase agreements with HS and OR provide power at LME-based variable rates for the duration of these agreements. In July 2021, Grundartangi reached an agreement with Landsvirkjun for an extension of its existing 161 MW power contract that would have expired in December 2023. Under the terms of the extension, Landsvirkjun will continue to supply power to Grundartangi from January 1, 2024 through December 31, 2026 and will increase the existing contract from 161 MW to 182 MW over time to provide the necessary flexibility to support the most recent capacity creep requirements and future growth opportunities for value-added products at the Grundartangi plant, including the Grundartangi casthouse project. In September 2022, this agreement was amended to provide for 42 MW at a fixed price and 119 MW at rates linked to Nord Pool plus transmission through 2023 and beginning January 1, 2024 through December 31, 2026, this agreement allows for fixed rates plus a small variable rate portion of the full 182 MW. Grundartangi also has a 25 MW power purchase agreement with Landsvirkjun at LME-based variable rates. 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 53% 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 May 31, 2024. Approximately 41% 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, 2023. Mt. Holly employees are not represented by a labor union. Approximately 38% 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. We are currently negotiating the terms of new agreements for both union 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, 2023, the principal and accrued interest for the contingent obligation was $30.2 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, 2023, 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.

Components of Accumulated Other

Components of Accumulated Other Comprehensive Loss	6 Months Ended
	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Components of Accumulated Other Comprehensive Loss	Components of Accumulated Other Comprehensive Loss Components of AOCL: June 30, 2023 December 31, 2022 Defined benefit plan liabilities $ (94.6) $ (98.0) Unrealized gain on financial instruments 1.7 1.7 Other comprehensive loss before income tax effect (92.9) (96.3) Income tax effect (1) 2.2 2.3 Accumulated other comprehensive loss $ (90.7) $ (94.0) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: June 30, 2023 December 31, 2022 Defined benefit plan liabilities $ 2.6 $ 2.6 Unrealized gain on financial instruments (0.4) (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, April 1, 2023 $ (94.4) $ 1.5 $ (92.9) Net amount reclassified to net income 2.2 0.0 2.2 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, April 1, 2022 $ (83.4) $ 1.7 $ (81.7) Net amount reclassified to net income 0.8 0.0 0.8 Balance, June 30, 2022 $ (82.6) $ 1.7 $ (80.9) Balance, January 1, 2023 $ (95.6) $ 1.6 $ (94.0) Net amount reclassified to net loss 3.4 (0.1) 3.3 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, January 1, 2022 $ (84.0) $ 1.7 $ (82.3) Net amount reclassified to net income 1.4 0.0 1.4 Balance, June 30, 2022 $ (82.6) $ 1.7 $ (80.9) Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended June 30, Six months ended June 30, AOCL Components Location 2023 2022 2023 2022 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 1.4 $ 0.5 $ 2.2 $ 0.9 Selling, general and administrative expenses 0.1 0.2 0.3 0.3 Other operating expense - net 0.7 0.3 0.9 0.5 Income tax effect — (0.1) — (0.2) Net of tax $ 2.2 $ 0.9 $ 3.4 $ 1.5 Unrealized gain (loss) on financial instruments Cost of goods sold $ 0.0 $ (0.1) $ (0.1) $ (0.1) Income tax effect 0.0 0.0 0.0 0.0 Net of tax $ 0.0 $ (0.1) $ (0.1) $ (0.1)

Components of Net Periodic Bene

Components of Net Periodic Benefit Cost	6 Months Ended
	Jun. 30, 2023
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, 2023 2022 2023 2022 Service cost $ 0.1 $ 1.0 $ 1.1 $ 2.1 Interest cost 4.4 2.6 7.0 5.1 Expected return on plan assets (1.7) (5.9) (7.5) (11.7) Amortization of prior service costs — 0.1 0.1 0.1 Amortization of net loss 2.4 1.0 3.2 1.7 Net periodic benefit cost (income) $ 5.2 $ (1.2) $ 3.9 $ (2.7) Other Postretirement Benefits Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Service cost $ 0.0 $ 0.0 $ 0.1 $ 0.1 Interest cost 1.2 0.6 1.9 1.3 Amortization of prior service cost — (0.5) — (1.0) Amortization of net loss (0.2) 0.3 0.1 0.8 Net periodic benefit cost $ 1.0 $ 0.4 $ 2.1 $ 1.2

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives As of June 30, 2023, we had an open position of 59,187 tonnes related to LME forward financial sales contracts to fix the forward LME aluminum price. These contracts are expected to settle monthly through December 2024. We have also entered 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, 2023, we had 2,961 tonnes related to fixed for floating swaps that will settle monthly through November 2023. We have entered into financial contracts to hedge a portion of Grundartangi's exposure to the Nord Pool power market (“Nord Pool power price swaps”). All of the Nord Pool power price swaps are expected to cash settle monthly through December 2023. The Nord Pool power price swaps are settled in Euros, therefore we have entered into financial contracts to hedge the risk of fluctuations associated with the Euro ("FX swaps"). As of June 30, 2023, we had an open position related to the FX swaps of €16.4 million that will settle monthly through December 2023. During the third quarter of 2022, we entered certain floating Nord Pool financial contracts to unwind a portion of our fixed contract position as a result of the recent power agreement amendment, making us predominantly hedged against Nord Pool power price fluctuations during 2023. As of June 30, 2023, we had an open net position of 499,116 MWh related to the Nord Pool power price swaps. We have entered into financial contracts to fix a portion of our exposure to the Indiana Hub power market at our Kentucky plants ("Indiana Hub power price swaps"). As of June 30, 2023, we had an open position of 88,320 MWh. The Indiana Hub power price swaps are expected to settle monthly through December 2023. 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 and the Sebree casthouse project denominated in these currencies ("casthouse currency hedges"). As of June 30, 2023, we had an open position related to the ISK casthouse swaps of kr24.0 million that will settle monthly through January 2024. As of June 30, 2023, we had an open position related to the Euro casthouse swaps of €4.9 that will settle monthly through January 2024. 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, 2023, we had an open position of 600,000 MMBtu. The NYMEX Henry Hub natural gas price swaps are expected to settle monthly through October 2023. 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, 2023 and December 31, 2022, 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, 2023 and December 31, 2022, respectively: Asset Fair Value June 30, 2023 December 31, 2022 Commodity contracts (1) $ 37.9 $ 129.1 Foreign exchange contracts (2) — — Total $ 37.9 $ 129.1 Liability Fair Value June 30, 2023 December 31, 2022 Commodity contracts (1) $ 3.4 $ 23.7 Foreign exchange contracts (2) 2.7 7.3 Total $ 6.1 $ 31.0 (1) Commodity contracts reflect our outstanding LME forward financial sales contracts, fixed for floating swaps, Nord Pool power price swaps, NYMEX Henry Hub natural gas price swaps, and Indiana Hub power price swaps. At June 30, 2023, $1.1 million of Due from affiliates, $1.0 million of Due to affiliates, and $1.5 million of Due to affiliates - less current portion were related to commodity contracts with Glencore. At December 31, 2022, $11.9 million of Due to affiliates, and $8.3 million of Due to affiliates - less current portion were related to commodity contract liabilities 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 June 30, Six months ended June 30, 2023 2022 2023 2022 Commodity contracts (1) $ 9.1 $ 237.0 $ (50.1) $ 181.3 Foreign exchange contracts 0.0 (5.2) 1.6 (6.2) Total $ 9.1 $ 231.8 $ (48.5) $ 175.1 (1) For the three months ended June 30, 2023, $11.4 million of the net gain was with Glencore, and for the three months ended June 30, 2022, $65.2 million of the net gain was with Glencore. For the six months ended June 30, 2023, $3.5 million of the net loss with Glencore, and for the six months ended June 30, 2022, $6.3 million of the net gain was with Glencore.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsOn July 7, 2023, Vlissingen borrowed $10.0 million on the Vlissingen Facility Agreement with Glencore International AG.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pay vs Performance Disclosure
Net income (loss) attributable to Century stockholders	$ 7.5	$ 37.4	$ (31.1)	$ 55.1

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2023
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

Acquisition of Jamalco (Tables)

Acquisition of Jamalco (Tables)	6 Months Ended
	Jun. 30, 2023
Business Combination and Asset Acquisition [Abstract]
Schedule of Fair Value of Assets Acquired and Liabilities Assumed	The following table summarizes the consideration transferred and the estimated fair value of identified assets acquired, liabilities assumed and noncontrolling interest at the date of acquisition: Preliminary purchase price allocation Amount Consideration transferred Cash paid $ 8.3 Total consideration transferred $ 8.3 Less: identifiable assets acquired and liabilities assumed Cash and cash equivalents $ 19.4 Restricted cash 8.3 Inventories 93.4 Accounts receivable - net 8.0 Prepaid and other current assets 7.7 Property, plant and equipment - net 102.2 Deferred tax assets 108.1 Other long-term assets 25.5 Accounts payable, trade (92.9) Accrued and other current liabilities (33.9) Asset retirement obligations (101.4) Total identifiable net assets acquired 144.4 Less: noncontrolling interest (32.8) Deferred credit - preliminary bargain purchase gain (103.3) Fair value allocated to net assets acquired, net of bargain purchase gain $ 8.3
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 and 2022, respectively, as if the acquisition of Jamalco had been completed on January 1, 2022. This unaudited pro forma financial information has been prepared for informational purposes and is not necessarily indicative of the actual consolidated results of operations had the acquisition been completed on January 1, 2022, nor is the information indicative of future results of operations of the combined companies. Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Revenue $ 595.3 $ 856.6 $ 1,177.6 $ 1,610.2 Earnings $ 6.7 $ 36.1 $ (33.0) $ 62.4

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2023
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 June 30, Six months ended June 30, 2023 2022 2023 2022 Net sales to Glencore $ 427.2 $ 483.5 $ 839.4 $ 916.6 Purchases from Glencore (1) 75.2 172.8 151.4 227.3 (1) Includes settlements of financial contract positions.

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2023
Revenue Recognition and Deferred Revenue [Abstract]
Disaggregation of revenue by geographical region	We disaggregate our revenue by geographical region as follows: Net Sales Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 United States $ 319.5 $ 583.4 $ 661.8 $ 1,089.5 Iceland 212.3 273.2 422.4 520.7 Jamaica 43.7 — 43.7 — Total $ 575.5 $ 856.6 $ 1,127.9 $ 1,610.2

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2023
Fair Value Disclosures [Abstract]
Financial assets and liabilities at fair value on a recurring basis	Recurring Fair Value Measurements As of June 30, 2023 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 5.8 $ — $ — $ 5.8 Trust assets (1) 1.1 — — 1.1 Derivative instruments — 37.9 — 37.9 TOTAL $ 6.9 $ 37.9 $ — $ 44.8 LIABILITIES: Derivative instruments — (6.1) — (6.1) TOTAL $ — $ (6.1) $ — $ (6.1) Recurring Fair Value Measurements As of December 31, 2022 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 5.6 $ — $ — $ 5.6 Trust assets (1) 0.1 — — 0.1 Derivative instruments — 127.3 1.8 129.1 TOTAL $ 5.7 $ 127.3 $ 1.8 $ 134.8 LIABILITIES: Derivative instruments — 26.4 4.6 31.0 TOTAL $ — $ 26.4 $ 4.6 $ 31.0 (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 or Level 3 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 Nord Pool power price swaps Discounted cash flows Quoted Nord Pool forward market Indiana Hub power price swaps Discounted cash flows Quoted Indiana Hub forward market FX swaps Discounted cash flows Euro/USD forward exchange rate Casthouse currency hedges Discounted cash flows Euro/USD forward exchange rate; ISK/USD forward exchange rate NYMEX Henry Hub natural gas price swaps Discounted cash flows Quoted NYMEX Henry Hub forward market The following table presents the inputs for recurring fair value measurements categorized within Level 3 of the fair value hierarchy, along with information regarding significant unobservable inputs used to value Level 3 assets and liabilities: Recurring Level 3 Fair Value Measurements: As of June 30, 2023 As of December 31, 2022 Asset / Liability Valuation Technique Observable Inputs Significant Unobservable Input Fair Value Value/Range of Unobservable Input Fair Value Value/Range of Unobservable Input LME forward financial sales contracts Discounted cash flows Quoted LME forward market Discount rate net (1) $ — 8.58% $ (2.8) 8.58% (1) Represents risk adjusted discount rate.
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 months ended June 30, 2023. Level 3 Assets Level 3 Liabilities For the three months ended June 30, 2022 LME Forward financial sales contracts LME forward financial sales contracts Casthouse currency hedges Balance as of April 1, 2022 $ — $ (16.7) $ — Total realized/unrealized gains (losses) Included in net income (1) — 12.9 — Transfers into Level 3 (2) 1.6 — 0.0 Balance as of June 30, 2022 $ 1.6 $ (3.8) $ 0.0 Change in unrealized gains (losses) (1) $ — $ 12.9 $ 0.0 (1) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts." (2) Transfers into Level 3 due to period of time remaining in derivative contract. For the six months ended June 30, 2023 Level 3 Assets Level 3 Liabilities 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) Transfers 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." Level 3 Assets Level 3 Liabilities For the six months ended June 30, 2022 LME forward financial sales contracts Nord Pool Swaps LME forward financial sales contracts FX Swaps Casthouse currency hedges Balance as of January 1, 2022 $ — $ 0.2 $ (5.1) $ (0.2) $ — Total realized/unrealized loss Included in net income (1) $ — $ — $ 3.8 $ — $ — Transfers into Level 3 (2) $ 1.6 $ — $ (2.5) $ — $ — Transfers out of Level 3 (3) $ — $ (0.2) $ — $ 0.2 $ — Balance as of June 30, 2022 $ 1.6 $ — $ (3.8) $ — $ — Change in unrealized gains (losses) (1) $ — $ — $ 3.8 $ — $ — ( 1) Gains and losses are presented in the Consolidated Statement of Operations within the line item "Net gain (loss) on forward and derivative contracts." (2) Transfers into Level 3 due to contracts with applied discount rate entered into during the six months ended June 30, 2022. (3) Transfers out of Level 3 due to period of time remaining in derivative contract.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2023
Earnings Per Share [Abstract]
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, 2023 2022 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net income attributable to Century stockholders $ 7.5 $ 37.4 Less: net income allocated to participating securities 0.4 2.3 Basic EPS: Net income allocated to common stockholders $ 7.1 92.3 $ 0.08 $ 35.1 91.2 $ 0.38 Effect of Dilutive Securities (1) : Share-based compensation (0.2) 0.9 (0.3) 1.6 Convertible senior notes — — 0.7 4.8 Diluted EPS: Net income allocated to common stockholders with assumed conversion $ 6.9 93.2 $ 0.07 $ 35.5 97.6 $ 0.36 For the six months ended June 30, 2023 2022 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net (loss) income attributable to Century stockholders $ (31.1) $ 55.1 Less: net income allocated to participating securities — 3.3 Basic EPS: Net (loss) income allocated to common stockholders $ (31.1) 92.3 $ (0.34) $ 51.8 91.2 $ 0.57 Effect of Dilutive Securities (1) : Share-based compensation — — (0.5) 1.9 Convertible senior notes — — 1.4 4.8 Diluted EPS: Net (loss) income allocated to common stockholders with assumed conversion $ (31.1) 92.3 $ (0.34) $ 52.7 97.9 $ 0.54 Three months ended June 30, Six months ended June 30, Securities excluded from the calculation of diluted EPS (in millions) (1) : 2023 2022 2023 2022 Share-based compensation — — 0.9 — Convertible preferred shares 5.4 5.9 5.4 5.9 Convertible notes 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, 2023
Inventory, Net [Abstract]
Schedule of inventories	Inventories consist of the following: June 30, 2023 December 31, 2022 Raw materials $ 117.6 $ 64.9 Work-in-process 86.4 46.0 Finished goods 44.4 58.0 Operating and other supplies 262.4 229.9 Total inventories $ 510.8 $ 398.8

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2023
Debt Disclosure [Abstract]
Schedule of debt	June 30, 2023 December 31, 2022 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) 63.2 90.0 Iceland Revolving Credit Facility (3) 73.0 35.0 Iceland Term Facility (4) 8.6 13.3 Debt classified as non-current liabilities: Grundartangi casthouse facility, net of financing fees of $0.7 million at June 30, 2023 (5) 69.3 49.4 Iceland Term Facility, net of financing fees of $0.0 million and current portion at June 30, 2023 (4) — 1.2 7.5% senior secured notes due April 1, 2028, net of financing fees of $3.0 million at June 30, 2023, interest payable semiannually 247.0 246.6 2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.7 million at June 30, 2023, interest payable semiannually 84.5 84.4 Total $ 553.4 $ 527.7 (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, 2023 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, 2023 was 9.00%. (3) We incur interest at base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2023 wa s 8.16%. (4) We incur interest at a rate equal to 3.2% plus EUR EURIBOR 1 month as published by the European Money Market Institute as defined within the agreement. The interest rate at June 30, 2023 was 6.46%. (5) We incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at June 30, 2023 was 8.63%.
Schedule of line of credit facilities	Status of our U.S. revolving credit facility: June 30, 2023 Credit facility maximum amount 250.0 Borrowing availability 160.0 Outstanding letters of credit issued 33.3 Outstanding borrowings 63.2 Borrowing availability, net of outstanding letters of credit and borrowings 63.5 Status of our Iceland revolving credit facility: June 30, 2023 Credit facility maximum amount 100.0 Borrowing availability 100.0 Outstanding letters of credit issued — Outstanding borrowings 73.0 Borrowing availability, net of borrowings 27.0

Components of Accumulated Oth_2

Components of Accumulated Other Comprehensive Loss (Tables)	6 Months Ended
	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated balances for each component of AOCI	Components of AOCL: June 30, 2023 December 31, 2022 Defined benefit plan liabilities $ (94.6) $ (98.0) Unrealized gain on financial instruments 1.7 1.7 Other comprehensive loss before income tax effect (92.9) (96.3) Income tax effect (1) 2.2 2.3 Accumulated other comprehensive loss $ (90.7) $ (94.0) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: June 30, 2023 December 31, 2022 Defined benefit plan liabilities $ 2.6 $ 2.6 Unrealized gain on financial instruments (0.4) (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, April 1, 2023 $ (94.4) $ 1.5 $ (92.9) Net amount reclassified to net income 2.2 0.0 2.2 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, April 1, 2022 $ (83.4) $ 1.7 $ (81.7) Net amount reclassified to net income 0.8 0.0 0.8 Balance, June 30, 2022 $ (82.6) $ 1.7 $ (80.9) Balance, January 1, 2023 $ (95.6) $ 1.6 $ (94.0) Net amount reclassified to net loss 3.4 (0.1) 3.3 Balance, June 30, 2023 $ (92.2) $ 1.5 $ (90.7) Balance, January 1, 2022 $ (84.0) $ 1.7 $ (82.3) Net amount reclassified to net income 1.4 0.0 1.4 Balance, June 30, 2022 $ (82.6) $ 1.7 $ (80.9)
Reclassification out of AOCI	Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended June 30, Six months ended June 30, AOCL Components Location 2023 2022 2023 2022 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 1.4 $ 0.5 $ 2.2 $ 0.9 Selling, general and administrative expenses 0.1 0.2 0.3 0.3 Other operating expense - net 0.7 0.3 0.9 0.5 Income tax effect — (0.1) — (0.2) Net of tax $ 2.2 $ 0.9 $ 3.4 $ 1.5 Unrealized gain (loss) on financial instruments Cost of goods sold $ 0.0 $ (0.1) $ (0.1) $ (0.1) Income tax effect 0.0 0.0 0.0 0.0 Net of tax $ 0.0 $ (0.1) $ (0.1) $ (0.1)

Components of Net Periodic Be_2

Components of Net Periodic Benefit Cost (Tables)	6 Months Ended
	Jun. 30, 2023
Retirement Benefits [Abstract]
Schedule of net periodic benefit cost	Pension Benefits Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Service cost $ 0.1 $ 1.0 $ 1.1 $ 2.1 Interest cost 4.4 2.6 7.0 5.1 Expected return on plan assets (1.7) (5.9) (7.5) (11.7) Amortization of prior service costs — 0.1 0.1 0.1 Amortization of net loss 2.4 1.0 3.2 1.7 Net periodic benefit cost (income) $ 5.2 $ (1.2) $ 3.9 $ (2.7) Other Postretirement Benefits Three months ended June 30, Six months ended June 30, 2023 2022 2023 2022 Service cost $ 0.0 $ 0.0 $ 0.1 $ 0.1 Interest cost 1.2 0.6 1.9 1.3 Amortization of prior service cost — (0.5) — (1.0) Amortization of net loss (0.2) 0.3 0.1 0.8 Net periodic benefit cost $ 1.0 $ 0.4 $ 2.1 $ 1.2

Derivatives (Tables)

Derivatives (Tables)	6 Months Ended
	Jun. 30, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
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, 2023 and December 31, 2022, respectively: Asset Fair Value June 30, 2023 December 31, 2022 Commodity contracts (1) $ 37.9 $ 129.1 Foreign exchange contracts (2) — — Total $ 37.9 $ 129.1 Liability Fair Value June 30, 2023 December 31, 2022 Commodity contracts (1) $ 3.4 $ 23.7 Foreign exchange contracts (2) 2.7 7.3 Total $ 6.1 $ 31.0 (1) Commodity contracts reflect our outstanding LME forward financial sales contracts, fixed for floating swaps, Nord Pool power price swaps, NYMEX Henry Hub natural gas price swaps, and Indiana Hub power price swaps. At June 30, 2023, $1.1 million of Due from affiliates, $1.0 million of Due to affiliates, and $1.5 million of Due to affiliates - less current portion were related to commodity contracts with Glencore. At December 31, 2022, $11.9 million of Due to affiliates, and $8.3 million of Due to affiliates - less current portion were related to commodity contract liabilities 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 June 30, Six months ended June 30, 2023 2022 2023 2022 Commodity contracts (1) $ 9.1 $ 237.0 $ (50.1) $ 181.3 Foreign exchange contracts 0.0 (5.2) 1.6 (6.2) Total $ 9.1 $ 231.8 $ (48.5) $ 175.1 (1) For the three months ended June 30, 2023, $11.4 million of the net gain was with Glencore, and for the three months ended June 30, 2022, $65.2 million of the net gain was with Glencore. For the six months ended June 30, 2023, $3.5 million of the net loss with Glencore, and for the six months ended June 30, 2022, $6.3 million of the net gain was with Glencore.

Acquisition of Jamalco - Narrat

Acquisition of Jamalco - Narrative (Details) - USD ($)		3 Months Ended	6 Months Ended
	May 02, 2023	Jun. 30, 2023	Jun. 30, 2023
General Alumina Holdings Limited
Business Acquisition [Line Items]
Total consideration transferred	$ 8,300,000
Other payments	1
Cash paid	$ 8,300,000
Transaction costs		$ 700,000	$ 1,600,000
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	May 02, 2023	Jun. 30, 2023	Dec. 31, 2022
Less: identifiable assets acquired and liabilities assumed
Deferred credit - preliminary bargain purchase gain		$ (103.3)	$ 0
General Alumina Holdings Limited
Consideration transferred
Cash paid	$ 8.3
Total consideration transferred	8.3
Less: identifiable assets acquired and liabilities assumed
Cash and cash equivalents	19.4
Restricted cash	8.3
Inventories	93.4
Accounts receivable - net	8
Prepaid and other current assets	7.7
Property, plant and equipment - net	102.2
Deferred tax assets	108.1
Other long-term assets	25.5
Accounts payable, trade	(92.9)
Accrued and other current liabilities	(33.9)
Asset retirement obligations	(101.4)
Total identifiable net assets acquired	144.4
Less: noncontrolling interest	(32.8)
Deferred credit - preliminary bargain purchase gain	(103.3)
Fair value allocated to net assets acquired, net of bargain purchase gain	$ 8.3

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, 2022	Jun. 30, 2023	Jun. 30, 2022
Business Acquisition [Line Items]
Revenue	$ 595.3	$ 856.6	$ 1,177.6	$ 1,610.2
Earnings	$ 6.7	$ 36.1	$ (33)	$ 62.4

Curtailment of Operations - H_2

Curtailment of Operations - Hawesville (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Curtailment Of Operations
Restructuring Cost and Reserve [Line Items]
Severance costs	$ 4.4		$ 11.4
Gain (loss) on material sales	0.5		1.2
Curtailment Of Operations | Temporary Facility Closing, Excess Capacity
Restructuring Cost and Reserve [Line Items]
Excess capacity charges	$ 3.6		$ 9
WARN Notice
Restructuring Cost and Reserve [Line Items]
Severance costs		$ 8.2		$ 8.2

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 09, 2022
Vlissingen facility agreement | Affiliated Entity | Vlissingen
Related Party Transaction [Line Items]
Credit facility maximum amount					$ 90
Stated interest rate, percentage					8.75%
Supply Commitment | Glencore
Related Party Transaction [Line Items]
Net sales to Glencore	$ 65.8	$ 13.9	$ 86.8	$ 13.9
Consolidated sales | Customer concentration risk | Glencore
Related Party Transaction [Line Items]
Major customer, percentage of revenue, net (percent)	74%	57%
Glencore
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners	42.90%		42.90%
Economic ownership percentage by related party	46.10%		46.10%

Related Party Transactions - Su

Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Related Party Transaction [Line Items]
Revenue	$ 575.5	$ 856.6	$ 1,127.9	$ 1,610.2
Related Party
Related Party Transaction [Line Items]
Revenue	427.2	483.5	839.4	916.6
Related Party | Glencore
Related Party Transaction [Line Items]
Revenue	427.2	483.5	839.4	916.6
Purchases from Glencore	$ 75.2	$ 172.8	$ 151.4	$ 227.3

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 575.5	$ 856.6	$ 1,127.9	$ 1,610.2
United States
Disaggregation of Revenue [Line Items]
Revenue	319.5	583.4	661.8	1,089.5
Iceland
Disaggregation of Revenue [Line Items]
Revenue	212.3	273.2	422.4	520.7
Jamaica
Disaggregation of Revenue [Line Items]
Revenue	$ 43.7	$ 0	$ 43.7	$ 0

Fair Value Measurements - Recur

Fair Value Measurements - Recurring Fair Value Measurements (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
ASSETS:
Cash equivalents	$ 5.8	$ 5.6
Trust assets	1.1	0.1
Derivative instruments	37.9	129.1
TOTAL	44.8	134.8
LIABILITIES:
Derivative instruments	(6.1)	31
TOTAL	(6.1)	31
Level 1
ASSETS:
Cash equivalents	5.8	5.6
Trust assets	1.1	0.1
Derivative instruments	0	0
TOTAL	6.9	5.7
LIABILITIES:
Derivative instruments	0	0
TOTAL	0	0
Level 2
ASSETS:
Cash equivalents	0	0
Trust assets	0	0
Derivative instruments	37.9	127.3
TOTAL	37.9	127.3
LIABILITIES:
Derivative instruments	(6.1)	26.4
TOTAL	(6.1)	26.4
Level 3
ASSETS:
Cash equivalents	0	0
Trust assets	0	0
Derivative instruments	0	1.8
TOTAL	0	1.8
LIABILITIES:
Derivative instruments	0	4.6
TOTAL	$ 0	$ 4.6

Fair Value Measurements - Signi

Fair Value Measurements - Significant Unobservable Inputs (Details) - Fixed to Variable London Metals Exchange Swap Net $ in Millions	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 0	$ (2.8)
Level 3 | Discount rate, net
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Value/Range of Unobservable Input	0.0858	0.0858

Fair Value Measurements - Level

Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
LME forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	$ 0	$ 1.8	$ 0
Total realized/unrealized gains (losses)
Included in net income	0		0
Transfers into Level 3	1.6		1.6
Transfers out of Level 3		(1.8)	0
Balance, ending	1.6	0	1.6
Change in unrealized gains (losses)	0	0	0
LME forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	(16.7)	(4.6)	(5.1)
Total realized/unrealized gains (losses)
Included in net income	12.9		3.8
Transfers into Level 3	0		(2.5)
Transfers out of Level 3		4.6	0
Balance, ending	(3.8)	0	(3.8)
Change in unrealized gains (losses)	12.9	$ 0	3.8
Casthouse currency hedges
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	0		0
Total realized/unrealized gains (losses)
Included in net income	0		0
Transfers into Level 3	0		0
Transfers out of Level 3			0
Balance, ending	0		0
Change in unrealized gains (losses)	0		0
Nord Pool Swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning			0.2
Total realized/unrealized gains (losses)
Included in net income			0
Transfers into Level 3			0
Transfers out of Level 3			(0.2)
Balance, ending	0		0
Change in unrealized gains (losses)			0
FX Swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning			(0.2)
Total realized/unrealized gains (losses)
Included in net income			0
Transfers into Level 3			0
Transfers out of Level 3			0.2
Balance, ending	$ 0		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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share [Abstract]
Net income (loss) attributable to Century stockholders	$ 7.5	$ 37.4	$ (31.1)	$ 55.1
Less: net income allocated to participating securities	0.4	2.3	0	3.3
Basic EPS:
Net (loss) income allocated to common stockholders	$ 7.1	$ 35.1	$ (31.1)	$ 51.8
Net (loss) income allocated to common stockholders (in shares)	92.3	91.2	92.3	91.2
Net (loss) income allocated to common stockholders (in dollars per share)	$ 0.08	$ 0.38	$ (0.34)	$ 0.57
Share-based compensation	$ (0.2)	$ (0.3)	$ 0	$ (0.5)
Share-based compensation (in shares)	0.9	1.6	0	1.9
Convertible senior notes	$ 0	$ 0.7	$ 0	$ 1.4
Convertible senior notes (in shares)	0	4.8	0	4.8
Diluted EPS:
Net (loss) income allocated to common stockholders with assumed conversion	$ 6.9	$ 35.5	$ (31.1)	$ 52.7
Net (loss) income allocated to common stockholders with assumed conversion (in shares)	93.2	97.6	92.3	97.9
Net (loss) income allocated to common stockholders with assumed conversion (in dollars per share)	$ 0.07	$ 0.36	$ (0.34)	$ 0.54

Earnings Per Share - Securities

Earnings Per Share - Securities Excluded (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based compensation
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	0	0	0.9	0
Convertible preferred shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	5.4	5.9	5.4	5.9
Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	4.6	0	4.6	0

Shareholders_ Equity (Details)

Shareholders’ Equity (Details) - USD ($)	3 Months Ended	99 Months Ended
	Mar. 31, 2015	Jun. 30, 2023	Dec. 31, 2022	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)		99,545,070	99,510,499
Common stock, shares, outstanding (in shares)		92,358,549	92,323,978
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	$ 0.01
Preferred shares issued (in shares)					160,000
Preferred shares outstanding (in shares)		53,706	53,854

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ (10)	$ 42.3	$ (10.2)	$ 44

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Inventory, Net [Abstract]
Raw materials	$ 117.6	$ 64.9
Work-in-process	86.4	46
Finished goods	44.4	58
Operating and other supplies	262.4	229.9
Total inventories	$ 510.8	$ 398.8

Debt - Activity (Details)

Debt - Activity (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022	Apr. 30, 2021
Debt Instrument [Line Items]
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly	$ 7.8	$ 7.8
Grundartangi casthouse debt facility	69.3	49.4
Convertible senior notes	84.5	84.4
Total debt	553.4	527.7
Industrial revenue bonds, variable
Debt Instrument [Line Items]
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly	$ 7.8	7.8
Maximum variable interest rate	12%
Effective interest rate	4.14%
Revolving credit facility | U.S. revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility	$ 63.2	90
Effective interest rate	9%
Revolving credit facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 73	35
Effective interest rate	8.16%
Casthouse Facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Secured debt	$ 69.3	49.4
Financing fees	$ 0.7
Effective interest rate	8.63%
Iceland term facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Revolving credit facility	$ 8.6	13.3
Secured debt	0	1.2
Financing fees	$ 0
Stated interest rate, percentage	3.20%
Effective interest rate	6.46%
Senior secured notes, 7.5% | Senior notes
Debt Instrument [Line Items]
Grundartangi casthouse debt facility	$ 247	246.6
Financing fees	$ 3
Stated interest rate, percentage	7.50%		7.50%
Senior convertible notes, 2.75% | Senior notes
Debt Instrument [Line Items]
Convertible senior notes	$ 84.5	$ 84.4
Financing fees	$ 1.7
Stated interest rate, percentage	2.75%

Debt - Narrative (Details)

Debt - Narrative (Details) - Senior notes	1 Months Ended
	Apr. 30, 2021 USD ($) $ / shares	Jun. 30, 2023 USD ($)
Senior secured notes, 7.5%
Line of Credit Facility [Line Items]
Stated interest rate, percentage	7.50%	7.50%
Face amount	$ 250,000,000
Proceeds from issuance of Senior Notes due 2028	245,200,000
Senior secured notes, 7.5% | Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument		$ 237,600,000
Convertible notes
Line of Credit Facility [Line Items]
Face amount	$ 86,300,000
Percentage of principal amount redeemed	100%
Proceeds from issuance of Convertible Senior Notes	$ 83,700,000
Conversion ratio	0.0533547
Conversion price (in dollars per share) | $ / shares	$ 18.74
Convertible notes | Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument		$ 66,600,000
Senior convertible notes, 2.75%
Line of Credit Facility [Line Items]
Stated interest rate, percentage		2.75%

Debt - Credit Facility (Details

Debt - Credit Facility (Details) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Jun. 14, 2022
U.S. revolving credit facility
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount	$ 150,000,000
U.S. revolving credit facility | U.S. revolving credit facility
Line of Credit Facility [Line Items]
Credit facility maximum amount			$ 250,000,000
Outstanding borrowings	63,200,000
Outstanding letters of credit issued	33,300,000
Credit facility maximum amount	250,000,000
Borrowing availability	160,000,000
Revolving credit facility	63,200,000	$ 90,000,000
Iceland revolving line of credit | U.S. revolving credit facility
Line of Credit Facility [Line Items]
Credit facility maximum amount	100,000,000
Outstanding borrowings	73,000,000
Outstanding letters of credit issued	0
Credit facility maximum amount	80,000,000
Borrowing availability	100,000,000
Revolving credit facility	$ 73,000,000	$ 35,000,000

Debt - U.S. Credit Facility Sch

Debt - U.S. Credit Facility Schedule (Details) - U.S. revolving credit facility - U.S. revolving credit facility $ in Millions	Jun. 30, 2023 USD ($)
Line of Credit Facility [Line Items]
Credit facility maximum amount	$ 250
Borrowing availability	160
Outstanding letters of credit issued	33.3
Outstanding borrowings	63.2
Borrowing availability, net of borrowings	$ 63.5

Debt - Iceland Credit Facility

Debt - Iceland Credit Facility Schedule (Details) - Iceland revolving line of credit - U.S. revolving credit facility $ in Millions	Jun. 30, 2023 USD ($)
Line of Credit Facility [Line Items]
Credit facility maximum amount	$ 100
Borrowing availability	100
Outstanding letters of credit issued	0
Outstanding borrowings	73
Borrowing availability, net of borrowings	$ 27

Debt - Casthouse and Surety (De

Debt - Casthouse and Surety (Details) € in Millions	1 Months Ended
	Nov. 30, 2021 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2023 EUR (€)	Dec. 09, 2022 USD ($)	Sep. 30, 2022 EUR (€)
Casthouse Facility
Debt Instrument [Line Items]
Debt instrument, term	8 years
Credit facility maximum amount	$ 130,000,000
Debt instrument, quarterly installment fee	1.739%
Debt instrument, remaining payment after drawdown of funds	60%
Medium-term notes, outstanding borrowings		$ 70,000,000
Medium-term Notes
Debt Instrument [Line Items]
Credit facility maximum amount | €					€ 13.6
Medium-term Notes | EURIBOR
Debt Instrument [Line Items]
Outstanding borrowings		$ 8,600,000	€ 8
Iceland term facility | Iceland revolving line of credit
Debt Instrument [Line Items]
Stated interest rate, percentage		3.20%	3.20%
Vlissingen facility agreement | Secured Debt | Vlissingen
Debt Instrument [Line Items]
Face amount				$ 90,000,000
Surety Bond
Debt Instrument [Line Items]
Loss contingency accrual		$ 6,600,000

Commitments and Contingencies (

Commitments and Contingencies (Details)			1 Months Ended		3 Months Ended		6 Months Ended	12 Months Ended
	Apr. 01, 2021	Aug. 18, 2017 USD ($)	Oct. 31, 2021 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2023 USD ($) laborUnion MW	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) laborUnion MW	Dec. 31, 2013 USD ($)	Sep. 30, 2022 MW	Jul. 31, 2021 MW
Labor Commitments [Abstract]
Percentage of total work force in union					53%		53%
Percentage of Grundartangi work force represented by the labor unions					87%		87%
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | laborUnion					5		5
Percentage of domestic based work force represented by a union					41%		41%
Percentage of foreign work force, represented by the union					0.38		0.38
Contingent consideration, accrued interest and principal					$ 30,200,000		$ 30,200,000
Netherlands
Labor Commitments [Abstract]
Percentage of Vlissingen work force represented by the labor union					100%		100%
PBGC
PBGC Settlement [Abstract]
Required pension contributions above minimum								$ 17,400,000
Payment for pension benefits					$ 0	$ 0
Pension contributions, amended term, annual contribution			$ 2,400,000		$ 2,400,000		$ 2,400,000
Pension contributions, amended term, total contribution			$ 9,600,000
Pension contributions, term			4 years
Santee Cooper
Power Contingencies [Abstract]
Power agreement, power supply, percentage	100%
Power supply agreement, increase production, at full capacity, percentage	75%
Grundartangi - HS, Landsvirkjun and OR
Power Contingencies [Abstract]
Power currently available under the power purchase agreement, available (in megawatts) | MW					545		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, extension (in megawatts) | MW									42	161
Power currently available under the power purchase agreement, requested (in megawatts) | MW										182
Power rate | MW									119
Ravenswood Retiree Medical Benefits Changes
Ravenswood litigation [Abstract]
Litigation settlement amount		$ 23,000,000
Ravenswood litigation settlement installment period		10 years					9 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, amount awarded to other party, annual payments							$ 2,000,000
Other current liabilities					$ 2,000,000		2,000,000
Other liabilities					$ 5,000,000		$ 5,000,000

Components of Accumulated Oth_3

Components of Accumulated Other Comprehensive Loss - Components of AOCL (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	$ (92.9)		$ (92.9)		$ (96.3)
Defined benefit plan liabilities	2.2		2.2		2.3
Accumulated other comprehensive loss	(90.7)		(90.7)		(94)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			399.3
Net amount reclassified to net income (loss)	2.2	$ 0.8	3.3	$ 1.4
Ending balance	372.9		372.9
Defined benefit plan liabilities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	(94.6)		(94.6)		(98)
Defined benefit plan liabilities	2.6		2.6		2.6
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(94.4)	(83.4)	(95.6)	(84)
Net amount reclassified to net income (loss)	2.2	0.8	3.4	1.4
Ending balance	(92.2)	(82.6)	(92.2)	(82.6)
Unrealized gain on financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	1.7		1.7		1.7
Defined benefit plan liabilities	(0.4)		(0.4)		$ (0.3)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.5	1.7	1.6	1.7
Net amount reclassified to net income (loss)	0	0	(0.1)	0
Ending balance	1.5	1.7	1.5	1.7
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(92.9)	(81.7)	(94)	(82.3)
Ending balance	$ (90.7)	$ (80.9)	$ (90.7)	$ (80.9)

Components of Accumulated Oth_4

Components of Accumulated Other Comprehensive Loss - Reclassifications out of AOCL (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	$ (559.6)	$ (840.7)	$ (1,063.9)	$ (1,501.1)
Selling, general and administrative expenses	(12)	(5.8)	(25.4)	(17.5)
Other operating expense - net	(4.6)	(0.2)	(11.8)	(0.4)
Income tax effect	10	(42.3)	10.2	(44)
Net income (loss) attributable to Century stockholders	7.5	37.4	(31.1)	55.1
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	1.4	0.5	2.2	0.9
Selling, general and administrative expenses	0.1	0.2	0.3	0.3
Other operating expense - net	0.7	0.3	0.9	0.5
Income tax effect	0	(0.1)	0	(0.2)
Net income (loss) attributable to Century stockholders	2.2	0.9	3.4	1.5
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	(0.1)	(0.1)	(0.1)
Income tax effect	0	0	0	0
Net income (loss) attributable to Century stockholders	$ 0	$ (0.1)	$ (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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0.1	$ 1	$ 1.1	$ 2.1
Interest cost	4.4	2.6	7	5.1
Expected return on plan assets	(1.7)	(5.9)	(7.5)	(11.7)
Amortization of prior service costs	0	0.1	0.1	0.1
Amortization of net loss	2.4	1	3.2	1.7
Net periodic benefit cost (income)	5.2	(1.2)	3.9	(2.7)
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0.1	0.1
Interest cost	1.2	0.6	1.9	1.3
Amortization of prior service costs	0	(0.5)	0	(1)
Amortization of net loss	(0.2)	0.3	0.1	0.8
Net periodic benefit cost (income)	$ 1	$ 0.4	$ 2.1	$ 1.2

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) - 6 months ended Jun. 30, 2023 € in Millions, kr in Millions	EUR (€) MMBTU MWh t	DKK (kr)
LME forward financial sales contracts
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) | t	59,187
Fixed For Floating Swaps
Derivative [Line Items]
Open position to offset fixed prices (in tonnes) | t	2,961
FX Swaps
Derivative [Line Items]
Derivative asset | €	€ 16.4
Nordpool Power Price Swap | Grundartangi
Derivative [Line Items]
Derivative liability (in MwH) | MWh	499,116
Indiana Hub Power Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) | MWh	88,320
USD ISK Forward Swap | Not designated as hedging instrument | Short
Derivative [Line Items]
Derivative, forward contracts | kr		kr 24
USD Euro Forward Swap | Not designated as hedging instrument | Short
Derivative [Line Items]
Derivative, forward contracts | €	€ 4.9
Henry Hub Natural Gas Price Swaps
Derivative [Line Items]
Derivative liability (in MwH) | MMBTU	600,000

Derivatives - Assets and Liabil

Derivatives - Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Due to affiliate, noncurrent	$ 11.1	$ 10.5
Related Party
Derivative [Line Items]
Due to affiliate, current	13.8	17
Commodity contracts | Related Party
Derivative [Line Items]
Due from affiliate, current	1.1
Due to affiliate, current	1	11.9
Due to affiliate, noncurrent	1.5	8.3
Not designated as hedging instrument
Derivative [Line Items]
Derivative asset	37.9	129.1
Derivative liability	6.1	31
Not designated as hedging instrument | Commodity contracts
Derivative [Line Items]
Derivative asset	37.9	129.1
Derivative liability	3.4	23.7
Not designated as hedging instrument | Foreign exchange contracts
Derivative [Line Items]
Derivative asset	0	0
Derivative liability	$ 2.7	$ 7.3

Derivatives - Net Gain (Loss) (

Derivatives - Net Gain (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	$ 9.1	$ 231.8	$ (48.5)	$ 175.1
Commodity contracts
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	9.1	237	(50.1)	181.3
Commodity contracts | Related Party | Glencore
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	11.4	65.2	(3.5)	6.3
Foreign exchange contracts
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	$ 0	$ (5.2)	$ 1.6	$ (6.2)

Subsequent Events (Details)

Subsequent Events (Details) $ in Millions	Jul. 07, 2023 USD ($)
Vlissingen facility agreement | Subsequent Event | Secured Debt | Vlissingen
Subsequent Event [Line Items]
Amount borrowed	$ 10

Uncategorized Items - cenx-2023

Label	Element	Value
Jamalco [Member]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual	$ 43,700,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual	$ 43,700,000