Century Aluminum (CENX) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2021	May 05, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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		90,087,714
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	2021
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
NET SALES
Related parties	$ 268.3	$ 271
Other customers	175.7	150.2
Total net sales	444	421.2
Cost of goods sold	464.7	416.4
Gross profit (loss)	(20.7)	4.8
Selling, general and administrative expenses	16.1	8.9
Other operating (income) expense - net	0.1	0.3
Operating income (loss)	(36.9)	(4.4)
Interest expense - Hawesville term loan	(0.3)	(0.7)
Interest expense	(9)	(6)
Interest income	0.1	0.1
Net gain (loss) on forward and derivative contracts	(98.1)	3.8
Other income (expense) - net	1.9	1.7
Income (loss) before income taxes	(142.3)	(5.5)
Income tax benefit (expense)	2.3	2.8
Net income (loss)	$ (140)	$ (2.7)
EARNINGS (LOSS) PER COMMON SHARE:
Basic and diluted (in dollars per share)	$ (1.55)	$ (0.03)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING:
Basic and diluted (in shares)	90.1	89.3

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Comprehensive income (loss):
Net income (loss)	$ (140)	$ (2.7)
Other comprehensive income before income tax effect:
Net income (loss) on foreign currency cash flow hedges reclassified as income	0	0
Defined benefit plans and other postretirement benefits:
Amortization of prior service benefit (cost) during the period	(0.8)	(0.8)
Amortization of net gain (loss) during the period	2.1	2.5
Other comprehensive income (loss) before income tax effect	1.3	1.7
Income tax effect	0	(0.3)
Other comprehensive income (loss)	1.3	1.4
Total comprehensive income (loss)	$ (138.7)	$ (1.3)

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ASSETS
Cash and cash equivalents	$ 26.3	$ 81.6
Restricted cash	1.2	2.7
Accounts receivable - net	57.4	51
Due from affiliates	21.3	10.3
Inventories	303	291.1
Derivative assets	13.8	6.4
Prepaid and other current assets	17.9	12.9
Total current assets	440.9	456
Property, plant and equipment - net	867.4	880.4
Due from affiliates - less current portion	0	1.7
Other assets	55.1	61.5
TOTAL	1,363.4	1,399.6
LIABILITIES:
Accounts payable, trade	116.2	106.1
Interest payable	0	15
Due to affiliates	39.7	21.7
Accrued and other current liabilities	62.3	54.5
Derivative liabilities	62.8	4.9
Accrued employee benefits costs	10.1	10.3
Hawesville term loan	15	20
U.S. revolving credit facility	50.4	0
Industrial revenue bonds	7.8	7.8
Total current liabilities	364.3	240.3
Senior notes payable	243.4	243.1
Iceland revolving credit facility	0	45
Accrued pension benefits costs - less current portion	63	65.2
Accrued postretirement benefits costs - less current portion	101.1	101.5
Other liabilities	67.3	44.8
Leases - right of use liabilities	23.2	24.3
Due to affiliates - less current portion	6.5	0.1
Deferred taxes	86.3	89.2
Total noncurrent liabilities	590.8	613.2
COMMITMENTS AND CONTINGENCIES	0	0
SHAREHOLDERS’ EQUITY:
Preferred stock	0	0
Common stock	1	1
Additional paid-in capital	2,530.9	2,530
Treasury stock, at cost	(86.3)	(86.3)
Accumulated other comprehensive loss	(117.5)	(118.8)
Accumulated deficit	(1,919.8)	(1,779.8)
Total shareholders’ equity	408.3	546.1
TOTAL	$ 1,363.4	$ 1,399.6

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ (140)	$ (2.7)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Unrealized (gain) loss on derivative instruments	94.4	(3.7)
Lower of cost or NRV inventory adjustment	0	13.4
Depreciation and amortization	20.9	20.2
Other non-cash items - net	3.2	(0.7)
Change in operating assets and liabilities:
Accounts receivable - net	(6.4)	17.2
Due from affiliates	(12.2)	20.2
Inventories	(11.8)	(10.4)
Prepaid and other current assets	(3.1)	0.1
Accounts payable, trade	(4.9)	(11.3)
Due to affiliates	7	(3.2)
Accrued and other current liabilities	3.8	(5.6)
Other - net	(0.7)	1.1
Net cash provided by (used in) operating activities	(49.8)	34.6
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(7.4)	(6)
Proceeds from sales of property, plant & equipment	0	0.1
Net cash provided by (used in) investing activities	(7.4)	(5.9)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments on Hawesville term loan	(5)	(5)
Borrowings under revolving credit facilities	197.6	121.8
Repayments under revolving credit facilities	(192.2)	(35.8)
Net cash provided by (used in) financing activities	0.4	81
CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(56.8)	109.7
Cash, cash equivalents and restricted cash, beginning of period	84.3	39.7
Cash, cash equivalents and restricted cash, end of period	27.5	149.4
Cash paid for:
Interest	16.1	0.8
Taxes	0	0
Non-cash investing activities:
Capital expenditures	$ 1.8	$ 1.2

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Preferred stock [Member]	Common stock [Member]	Additional paid-in capital [Member]	Treasury stock, at cost [Member]	Accumulated other comprehensive loss [Member]	Accumulated deficit [Member]
Balance, start at Dec. 31, 2019	$ 675	$ 0	$ 1	$ 2,526.5	$ (86.3)	$ (109.8)	$ (1,656.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(2.7)						(2.7)
Other comprehensive income (loss)	1.4					1.4
Share-based compensation	0.1	0	0	0.1
Conversion of preferred stock to common stock	0	0	0	0
Balance, end at Mar. 31, 2020	673.8	0	1	2,526.6	(86.3)	(108.4)	(1,659.1)
Balance, start at Dec. 31, 2020	546.1	0	1	2,530	(86.3)	(118.8)	(1,779.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(140)						(140)
Other comprehensive income (loss)	1.3					1.3
Share-based compensation	0.9	0	0	0.9
Conversion of preferred stock to common stock	0	0	0	0
Balance, end at Mar. 31, 2021	$ 408.3	$ 0	$ 1	$ 2,530.9	$ (86.3)	$ (117.5)	$ (1,919.8)

General

General	3 Months Ended
	Mar. 31, 2021
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, 2020. In management’s opinion, the unaudited interim consolidated financial statements reflect all adjustments, which are of a normal and recurring nature, that are necessary for a fair presentation of financial results for the interim periods presented. Operating results for the first three months of 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. Throughout this Form 10-Q, and unless expressly stated otherwise or as the context otherwise requires, "Century Aluminum," "Century," the "Company," "we," "us," "our" and "ours" refer to Century Aluminum Company and its consolidated subsidiaries. Recently Adopted Accounting Standards On January 1, 2021, we adopted Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." The ASU amendments include the removal of certain exceptions to the general principles of ASC 740 and to improve and simplify accounting for income taxes by clarifying and amending existing guidance. The adoption of the ASU did not have a material effect on the Company’s consolidated financial statements. On January 1, 2021, we adopted FASB ASU 2020-06, “Debt With Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity" using the modified retrospective method. The ASU amendments include simplification of the accounting models for convertible instruments and conversion options, and amendments to diluted earnings per share (“EPS”) calculations for certain convertible instruments, requiring the inclusion of convertible securities in the calculation of diluted EPS using the if-converted method. The adoption of the ASU did not have a material effect on the Company’s consolidated financial statements. On January 1, 2021, we adopted the final rule issued by the Securities and Exchange Commission (“SEC”) that amends the disclosure requirements related to issuers and guarantors of certain registered securities under SEC Regulation S-X Rule 3-10. We presented the alternative financial disclosures in Item 2 . Management's Discussion a n d A nalysis - Liquidity and Capital Resources . The adoption of the SEC rule is limited to disclosures only and did not have a material effect on the Company’s consolidated financial statements.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The significant related party transactions occurring during the three months ended March 31, 2021 and 2020 are described below. We believe all of our transactions with related parties are at prices that approximate market. Glencore ownership As of March 31, 2021, Glencore plc and its affiliates (together "Glencore") beneficially owned 42.9% of Century’s outstanding common stock (46.7% on a fully-diluted basis assuming the conversion of all of the Series A Convertible Preferred Stock) and all of our outstanding Series A Convertible Preferred Stock. See Note 6. 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 debt transactions. Sales to Glencore For the three months ended March 31, 2021 and 2020, we derived approximately 60% and 64%, respectively, of our consolidated net sales from Glencore. Glencore purchases aluminum produced at our U.S smelters at prices primarily based on the London Metal Exchange (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 also entered into agreements with Glencore pursuant to which we sell certain amounts of alumina at market-based prices. For the three months ended March 31, 2021, we recorded no revenue related to alumina sales to Glencore, and for the three months ended March 31, 2020, we recor ded $0.3 million of revenue related to alumina sales to Glencore, respectively. Purchases from Glencore We purchase a portion of our alumina and certain other raw material requirements from Glencore. Alumina purchases from Glencore during the three months ended March 31, 2021 were priced based on published alumina and aluminum indices. Financial contracts with Glencore We have certain financial contracts with Glencore. See Note 13. Derivatives regarding these forward financial sales contracts. Hawesville Term Loan On April 29, 2019, we entered into a loan agreement with Glencore Ltd. pursuant to which the Company borrowed $40.0 million (the "Hawesville Term Loan”). See Note 9. Debt for additional information. Summary A summary of the aforementioned significant related party transactions is as follows: Three months ended March 31, 2021 2020 Net sales to Glencore $ 268.3 $ 271.0 Purchases from Glencore 72.3 40.2 .

Revenue

Revenue	3 Months Ended
	Mar. 31, 2021
Revenue Recognition and Deferred Revenue [Abstract]
Revenue	Revenue We disaggregate our revenue by geographical region as follows: Net Sales Three months ended March 31, 2021 2020 United States $ 276.2 $ 274.1 Iceland 167.8 147.1 Total $ 444.0 $ 421.2

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
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 - significant unobservable inputs for the asset or liability. Recurring Fair Value Measurements As of March 31, 2021 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 13.3 $ — $ — $ 13.3 Trust assets (1) 1.5 — — 1.5 Derivative instruments — 14.8 0.0 14.8 TOTAL $ 14.8 $ 14.8 $ — $ 29.6 LIABILITIES: Contingent obligation – net $ — $ — $ — $ — Derivative instruments — 104.8 6.2 111.0 TOTAL $ — $ 104.8 $ 6.2 $ 111.0 Recurring Fair Value Measurements As of December 31, 2020 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 54.2 $ — $ — $ 54.2 Trust assets (1) — — — — Derivative instruments — 12.1 3.0 15.1 TOTAL $ 54.2 $ 12.1 $ 3.0 $ 69.3 LIABILITIES: Contingent obligation – net $ — $ — $ — $ — Derivative instruments — 16.7 — 16.7 TOTAL $ — $ 16.7 $ — $ 16.7 (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 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 FX swaps Discounted cash flows Euro/USD forward exchange rate 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 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: Level 3 Fair Value Measurements: Asset / Liability Fair Value at March 31, 2021 Valuation Technique Observable Inputs Significant Unobservable Input Value/Range of Unobservable Input LME forward financial sales contracts $ (6.0) Discounted cash flows Quoted LME forward market Discount rate net (1) 10.00% Contingent obligation $ — Discounted cash flows Quoted LME forward market, management's estimate of the LME forward market prices for periods beyond the quoted periods, management's estimates of future level of operations Management's estimates of the LME forward market price beyond the quoted periods (2) $2,217/T-$2,321/T FX swaps $ (0.2) Discounted cash flows Euro/USD forward exchange rate Discount rate net (1) 10.00% (1) Represents risk adjusted discount rate. (2) Represents the range of estimated forward LME prices of primary aluminum through the term of the agreement in December 2028. The following table presents the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis. Level 3 Liabilities For the three months ended March 31, 2021 LME forward financial sales contracts FX Swaps Balance as of January 1, 2021 $ 2.9 $ 0.1 Total realized/unrealized gains (losses) Included in net income (loss) (1) (8.7) — Purchases, sales, settlements Purchases — — Sales — — Settlements — — Transfers into Level 3 (2) (0.7) (0.2) Transfers out of Level 3 (3) 0.5 (0.1) Balance as of March 31, 2021 (6.0) $ (0.2) Change in unrealized gains (losses) (1) $ (8.7) $ — (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 during the first quarter of 2021. (3) Transfers out of Level 3 due to period of time remaining in derivative contract. For the three months ended March 31, 2020 Level 3 Assets Level 3 Liabilities U.S. LME forward financial sales contracts Hawesville L4 Power Price Swaps Balance as of January 1, 2020 $ 10.6 $ (2.9) Total realized/unrealized gains (losses) Included in Net Income (1) 6.7 (1.5) Purchases, sales, settlements Purchases — — Sales — — Settlements — 1.2 Transfers into Level 3 (2) — — Transfers out of Level 3 (3) (9.5) — Balance as of March 31, 2020 $ 7.8 $ (3.2) Change in unrealized gains (losses) (1) $ 6.7 $ (0.3) (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 during the first quarter of 2020.

Earnings (Loss) Per Share

Earnings (Loss) Per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings (Loss) Per Share	Earnings (Loss) Per Share Basic earnings (loss) per share ("EPS") amounts are calculated by dividing net income (loss) allocated to common stockholders by the weighted average number of common shares outstanding 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 earnings (loss) per share: For the three months ended March 31 2021 2020 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net income (loss) $ (140.0) $ (2.7) Amount allocated to common stockholders 100.0 % 100.0 % Basic and diluted EPS (1) $ (140.0) 90.1 $ (1.55) $ (2.7) 89.3 $ (0.03) Three months ended March 31, Securities excluded from the calculation of diluted EPS (in millions) (1) : 2021 2020 Share-based compensation 2.2 0.4 Convertible preferred shares (2) 6.4 — (1) In periods when we report a net loss, all share-based compensation awards and convertible preferred shares 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	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity Note [Abstract]
Shareholders’ Equity	Shareholders’ Equity Common Stock As of March 31, 2021 and December 31, 2020, we had 195,000,000 shares of common stock, $0.01 par value per share, authorized under our Restated Certificate of Incorporation, of which 97,274,235 shares were issued and 90,087,714 shares were outstanding at March 31, 2021; 97,242,318 shares were issued and 90,055,797 shares were outstanding at December 31, 2020. 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 March 31, 2021 and December 31, 2020, we had 5,000,000 shares of preferred stock, $0.01 par value per share, authorized under our Restated Certificate of Incorporation. Our Board of Directors may issue preferred stock in one or more series and determine for each series the dividend rights, conversion rights, voting rights, redemption rights, liquidating preferences, sinking fund terms and the number of shares constituting that series, as well as the designation thereof. Depending upon the terms of preferred stock established by our Board of Directors, any or all of the preferred stock could have preference over the common stock with respect to dividends and other distributions and upon the liquidation of Century. In addition, issuance of any shares of preferred stock with voting powers may dilute the voting power of the outstanding common stock. Series A Convertible Preferred Stock Shares Authorized and Outstanding . In 2008, we issued 160,000 shares of our Series A Convertible Preferred Stock. Glencore holds all of the issued and outstanding Series A Convertible Preferred Stock. At March 31, 2021 and December 31, 2020, there were 63,452 and 63,589 shares of Series A Convertible Preferred Stock 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 ratio of preferred to common shares is 100 shares of common stock for each share of preferred stock. The Common and Preferred Stock table below contains additional information about preferred stock conversions during the three months ended March 31, 2021 and 2020. Preferred stock Common stock Common and Preferred Stock Activity (in shares): Series A Convertible Treasury Outstanding Beginning balance as of December 31, 2020 63,589 7,186,521 90,055,797 Conversion of convertible preferred stock (137) — 13,697 Issuance for share-based compensation plans — — 18,220 Ending balance as of March 31, 2021 63,452 7,186,521 90,087,714 Beginning balance as of December 31, 2019 67,323 7,186,521 89,185,661 Conversion of convertible preferred stock (1,182) — 118,146 Issuance for share-based compensation plans — — 157,158 Ending balance as of March 31, 2020 66,141 7,186,521 89,460,965 Stock Repurchase Program In 2011, our Board of Directors authorized a $60.0 million common stock repurchase program and during the first quarter of 2015, our Board of Directors increased the size of the program by $70.0 million. Under the program, Century is authorized to repurchase up to $130.0 million of our outstanding shares of common stock, from time to time, on the open market at prevailing market prices, in block trades or otherwise. The timing and amount of any shares repurchased will be determined by our management based on its evaluation of market conditions, the trading price of our common stock and other factors. The stock repurchase program may be suspended or discontinued at any time. Shares of common stock repurchased are recorded at cost as treasury stock and result in a reduction of shareholders’ equity in the consolidated balance sheets. From time to time, treasury shares may be reissued as contributions to our employee benefit plans and for the conversion of convertible preferred stock. When shares are reissued, we use an average cost method for determining cost. The difference between the cost of the shares and the reissuance price is added to or deducted from additional paid-in capital.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We recorded an income tax benefit of $2.3 million and $2.8 million for the three months ended March 31, 2021 and 2020, respectively. The change is primarily due to improved operational results from foreign operations in the current quarter. Our income tax benefit or expense is based on an annual effective tax rate forecast, including estimates and assumptions that could change during the year. The application of the accounting requirements for income taxes in interim periods, after consideration of our valuation allowance, causes a significant variation in the typical relationship between income tax expense/benefit and pre-tax accounting income/loss.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2021
Inventory, Net [Abstract]
Inventories	Inventories Inventories consist of the following: March 31, 2021 December 31, 2020 Raw materials $ 105.2 $ 95.9 Work-in-process 44.1 40.5 Finished goods 22.7 26.9 Operating and other supplies 131.0 127.8 Total inventories $ 303.0 $ 291.1 Inventories are stated at the lower of cost or Net Realizable Value ("NRV") using the first-in, first-out ("FIFO") or the weighted average cost method.

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt March 31, 2021 December 31, 2020 Debt classified as current liabilities: Hawesville Term Loan (1) $ 15.0 $ 20.0 Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) (2) 7.8 7.8 U.S. Revolving Credit Facility (3) 50.4 — Debt classified as non-current liabilities: Iceland Revolving Credit Facility (4) — 45.0 12.0% senior secured notes due July 1, 2025, net of debt discount of $2.2 million and $2.3 million, and financing fees of $4.4 million and $4.6 million at March 31, 2021 and December 31, 2020, respectively, interest payable semiannually 243.4 243.1 Total $ 316.6 $ 315.9 (1) See "Hawesville Term Loan" below. At March 31, 2021, the applicable interest rate was LIBOR of 0.2% plus margin of 5.375% and there is no interest payable outstanding. As of March 31, 2021, we have made $25.0 million of principal payments and $2.2 million of interest payments. (2) 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 IRBs interest rate at March 31, 2021 was 0.2%. (3) We have elected to incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at March 31, 2021 was 3.8%. (4) We have elected to incur interest at LIBOR plus applicable margin as defined within the agreement. 12.0% Notes due 2025 General. On July 1, 2020, we issued $250.0 million in aggregate principal amount of 12.0% senior secured notes due 2025 (the "2025 Notes"). The 2025 Notes were issued at a discount and we received proceeds of $243.8 million, prior to payment of certain financing fees and related expenses. Fair Value. Fair value for our 2025 Notes, based on the latest trading data available, was $268.8 million as of March 31, 2021. 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. In connection with the offering of the 2028 Notes described below, we commenced a cash tender offer to purchase any and all of our outstanding 2025 Notes at par plus a tender premium of $14.6 million. On April 14, 2021, we purchased $195.9 million aggregate principal amount of the 2025 Notes in the tender offer, and notified the holders of all outstanding 2025 Notes that were not purchased in the tender offer of our election to redeem all such remaining 2025 Notes on May 14, 2021. 7.5% Senior Secured Notes due 2028 As disclosed in N ote 14. Subsequent E vents , on April 14, 2021, we issued $250.0 million in aggregate principal amount of senior secured notes due 2028 (the "2028 Notes"). The 2028 Notes bear interest semi-annually in arrears on April 1 and October 1 of each year, beginning on October 1, 2021, at a rate of 7.5% per annum in cash. Convertible Notes due 2028 In addition, as disclosed in Note 14. Subsequent E vents , on April 9, 2021, we completed a private offering of $86.3 million aggregate principal amount of convertible senior notes due 2028 (the "Convertible Notes"). The Convertible Notes were issued at a price of 100% of their aggregate principal amount, will pay interest semi-annually in arrears on May 1 and November 1 of each year, beginning on November 1, 2021, at a rate of 2.75% per annum in cash, and will mature on May 1, 2028, unless earlier converted, repurchased, or redeemed. Hawesville Term Loan On April 29, 2019, we entered into a loan agreement with Glencore Ltd. pursuant to which the Company borrowed $40.0 million. Borrowings under the Hawesville Term Loan were used to partially finance the second phase of the Hawesville restart project. The Hawesville Term Loan matures on December 31, 2021 and is to be repaid in twenty-four (24) equal monthly installments of principal beginning on January 31, 2020. The Hawesville Term Loan bears interest, due monthly, at a floating rate equal to LIBOR plus 5.375% per annum. The Hawesville Term Loan is not secured by any collateral. U.S. Revolving Credit Facility We and certain of our direct and indirect domestic subsidiaries ("the Borrowers") have a senior secured revolving credit facility with a syndicate of lenders (as amended from time to time, the "U.S. revolving credit facility"). The U.S. revolving credit facility provides for borrowings of up to $175.0 million in the aggregate, including up to $110.0 million under a letter of credit sub-facility, and also includes an uncommitted accordion feature whereby borrowers may increase the capacity of the U.S. revolving credit facility by up to $50.0 million, subject to agreement with the lenders. The U.S. revolving credit facility matures on May 16, 2023. 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 March 31, 2021, there were $50.4 million in outstanding borrowings 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: March 31, 2021 Credit facility maximum amount $ 175.0 Borrowing availability 139.6 Outstanding letters of credit issued 75.4 Outstanding borrowings 50.4 Borrowing availability, net of outstanding letters of credit and borrowings 13.8 Iceland Revolving Credit Facility Our wholly-owned subsidiary, Nordural Grundartangi ehf ("Grundartangi"), has entered into a $50.0 million revolving credit facility agreement with Landsbankinn hf., dated November 2013, as amended (the "Iceland revolving credit facility"). At March 31, 2021, there were no outstanding borrowings under our Iceland revolving credit facility. The Iceland revolving credit facility has a term through November 2022. Principal payments, if any, are due upon maturity of the Iceland revolving credit facility and may be prepaid without penalty. Status of our Iceland revolving credit facility: March 31, 2021 Credit facility maximum amount $ 50.0 Borrowing availability 50.0 Outstanding letters of credit issued — Outstanding borrowings — Borrowing availability, net of borrowings 50.0

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
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 Vernon In July 2006, we were named as a defendant, together with certain affiliates of Alcan Inc., in a lawsuit brought by Alcoa Inc. seeking to determine responsibility for certain environmental indemnity obligations related to the sale of a cast aluminum plate manufacturing facility located in Vernon, California, which we purchased from Alcoa Inc. in December 1998, and sold to Alcan Rolled Products-Ravenswood LLC in July 1999. The complaint also seeks costs and attorney fees. The matter was stayed by the court in 2008 to allow for the remediation of environmental areas at the site. On June 30, 2016, the U.S. District Court for the District of Delaware ordered the stay lifted and reopened the case. Discovery was completed in the third quarter of 2019. Trial was bifurcated and moved to September 2021 for Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA") issues and to a later undetermined date for questions of fact. At this stage, we cannot predict the ultimate outcome of this action or estimate a range of reasonably possible losses related to this matter. 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 March 31, 2021, $2.0 million was recorded in other current liabilities and $7.7 million was recorded in other liabilities. PBGC Settlement In 2013, we entered into a settlement agreement with the Pension Benefit Guarantee Corporation ("PBGC") regarding an alleged "cessation of operations" at our Ravenswood facility. Pursuant to the terms of the 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 are able to defer one or more of these payments, provided that we provide the PBGC with acceptable security for such deferred payments. We did not make any contributions for the three month periods ended March 31, 2021, and 2020. We have elected to defer certain payments under the PBGC agreement and have provided the PBGC with the appropriate security. The remaining contributions under this agreement are approximately $9.6 million. Environmental Contingencies Matters relating to the St. Croix Alumina Refining Facility We are a party to a United States Environmental Protection Agency Administrative Order on Consent (the "Order") pursuant to which certain past and present owners of an alumina refining facility at St. Croix, Virgin Islands (the "St. Croix Alumina Refinery") have agreed to carry out a Hydrocarbon Recovery Plan to remove and manage hydrocarbons floating on groundwater underlying the facility. Pursuant to the Hydrocarbon Recovery Plan, recovered hydrocarbons and groundwater are delivered to the adjacent petroleum refinery where they are received and managed. In October 2020, parties participating in the Hydrocarbon Recovery Plan filed a complaint against Century and Virgin Islands Alumina Corporation, L.L.C. relating to the Hydrocarbon Recover Plan. The deadline to respond to the complaint has been postponed by all parties until May 27, 2021. At this time, we are not able to estimate the amount of any future potential payments under this indemnification to comply with the Order, but we do not anticipate that any such amounts will have a material adverse effect on our financial condition, results of operations or liquidity, regardless of the final outcome. In December 2010, Century was among several defendants named in a lawsuit filed by plaintiffs who either worked, resided or owned property in the area downwind from the St. Croix Alumina Refinery. In March 2011, Century was also named a defendant in a nearly identical suit brought by certain additional plaintiffs. The plaintiffs in both suits allege damages caused by the presence of red mud and other particulates coming from the alumina facility and are seeking unspecified monetary damages, costs and attorney fees as well as certain injunctive relief. We tendered indemnity and defense to St. Croix Alumina LLC and Alcoa Alumina & Chemical LLC under the terms of an acquisition agreement relating to the facility and have filed motions to dismiss plaintiffs’ claims. In August 2015, the Superior Court of the Virgin Islands, Division of St. Croix denied the motions to dismiss but ordered all plaintiffs to refile individual complaints. On February 28, 2018, plaintiffs in both cases filed a Motion for Voluntary Dismissal of Century without prejudice to refiling. At this time, it is not possible to predict the ultimate outcome of or to estimate a range of reasonably possible losses for any of the foregoing actions relating to the St. Croix Alumina Refinery. 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 has an effective term through May 2022. Each of these agreements provide for automatic extension on a year-to-year basis unless a one year notice is given. 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 has an effective term through May 2022. Each of these agreements provides for automatic extension on a year-to-year basis unless a one year notice is given. Mt. Holly CASC has a power supply agreement with Santee Cooper that has an effective term beginning April 1, 2021 and runs 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 is expected to provide sufficient energy to allow Mt. Holly to increase its production to 75% of full production capacity. Grundartangi Grundartangi has power purchase agreements for approximately 525 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 2023 through 2036 (subject to extension). The power purchase agreements with HS and OR both provide power at LME-based variable rates for the duration of these agreements. The power purchase agreement with Landsvirkjun for 161 MW provides power at rates linked to the Nord Pool power market. Helguvik Nordural Helguvik ehf ("Helguvik") has a power purchase agreement with OR to provide a portion of the power requirements to the Helguvik project. The agreement would provide power at LME-based variable rates and contain take-or-pay obligations with respect to a significant percentage of the total committed and available power under such agreement. The first phase of power under the OR purchase agreement (approximately 47.5 MW) became available in the fourth quarter of 2011 and is currently being utilized at Grundartangi. The agreement also contains certain conditions to OR’s obligations with respect to the remaining phases and OR has alleged that certain of these conditions have not been satisfied. Other Commitments and Contingencies Labor Commitments The bargaining unit employees at our Grundartangi, Vlissingen, Hawesville and Sebree facilities are represented by labor unions, representing approximately 66% of our total workforce. Approximately 85% 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 FME since Vlissingen is a member of 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 expired on December 1, 2020 and since such time we have been operating under the terms of the expired agreement while we engage in negotiations regarding the terms of a new labor agreement. Approximately 58% of our U.S. based work force is represented by USW. On April 16, 2021, a new labor agreement for Hawesville employees was reached, running through April 1, 2026. Refer to Note 14. Subse quent Events for further detail. 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.

Components of Accumulated Other

Components of Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Components of Accumulated Other Comprehensive Loss	Components of Accumulated Other Comprehensive Loss Components of AOCL: March 31, 2021 December 31, 2020 Defined benefit plan liabilities $ (122.3) $ (123.7) Unrealized gain (loss) on financial instruments 2.1 2.1 Other comprehensive loss before income tax effect (120.2) (121.6) Income tax effect (1) 2.7 2.8 Accumulated other comprehensive loss $ (117.5) $ (118.8) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: March 31, 2021 December 31, 2020 Defined benefit plan liabilities $ 3.1 $ 3.2 Unrealized loss on financial instruments (0.4) (0.4) The following table summarizes the changes in the accumulated balances for each component of AOCL: Defined benefit plan and other postretirement liabilities Unrealized gain (loss) on financial instruments Total, net of tax Balance, January 1, 2021 $ (120.6) $ 1.8 $ (118.8) Net amount reclassified to net income (loss) 1.3 0.0 1.3 Balance, March 31, 2021 $ (119.3) $ 1.8 $ (117.5) Balance, January 1, 2020 $ (111.7) $ 1.9 $ (109.8) Net amount reclassified to net income 1.4 0.0 1.4 Balance, March 31, 2020 $ (110.3) $ 1.9 $ (108.4) Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended March 31, AOCL Components Location 2021 2020 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 0.8 $ 1.1 Selling, general and administrative expenses 0.2 0.2 Other operating expense, net 0.4 0.4 Income tax effect (0.1) (0.3) Net of tax $ 1.3 $ 1.4 Unrealized loss on financial instruments Cost of goods sold $ 0.0 $ 0.0 Income tax effect 0.0 0.0 Net of tax $ 0.0 $ 0.0

Components of Net Periodic Bene

Components of Net Periodic Benefit Cost	3 Months Ended
	Mar. 31, 2021
Components of net periodic benefit cost [Abstract]
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost Pension Benefits Three months ended March 31, 2021 2020 Service cost $ 1.4 $ 1.3 Interest cost 2.4 2.8 Expected return on plan assets (5.5) (5.1) Amortization of prior service costs 0.0 0.0 Amortization of net loss 1.5 1.5 Net periodic benefit cost $ (0.2) $ 0.5 Other Postretirement Benefits ("OPEB") Three months ended March 31, 2021 2020 Service cost $ 0.1 $ 0.1 Interest cost 0.6 0.8 Amortization of prior service cost (0.8) (0.8) Amortization of net loss 0.6 1.0 Net periodic benefit cost $ 0.5 $ 1.1

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives As of March 31, 2021, we had an open position of 175,716 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 also had an open position of 418,500 tonnes related to Midwest Premium ("MWP") forward financial sales contracts to fix the forward MWP price. These contracts are expected to settle through December 2022. 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 March 31, 2021, we had 16,482 tonnes related to fixed for floating swaps that will settle at various dates through March 2022. We previously have entered into financial contracts to hedge a portion of our exposure at our U.S. operations to the NYMEX Henry Hub ("NYMEX Henry Hub natural gas price swaps"). As of March 31, 2021, the NYMEX Henry Hub natural gas swaps had fully matured. 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”). As of March 31, 2021, we had an open position of 1,815,075 MWh related to the Nord Pool power price swaps. The Nord Pool power price swaps are expected to settle monthly through December 2023. Because the Nord Pool power price swaps are settled in Euros, we have entered into financial contracts to hedge the risk of fluctuations associated with the Euro ("FX swaps"). As of March 31, 2021, we had an open position related to the FX swaps of €42.2 million that will settle monthly through December 2023. The following table sets forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of March 31, 2021 and December 31, 2020, respectively: Asset Fair Value March 31, 2021 December 31, 2020 Commodity contracts (1) $ 14.4 $ 12.8 Foreign exchange contracts (2) 0.4 2.4 Total $ 14.8 $ 15.2 Liability Fair Value March 31, 2021 December 31, 2020 Commodity contracts (1) $ 110.5 $ 16.7 Foreign exchange contracts (2) 0.5 — Total $ 111.0 $ 16.7 (1) Commodity contracts reflect our outstanding LME forward financial sales contracts, MWP forward financial sales contracts, fixed for floating swaps, and Nord Pool power price swaps. At March 31, 2021, $22.3 million of Due to affiliates and $6.5 million of Due to affiliates - less current portion was related to commodity contract liabilities with Glencore. At December 31, 2020, $1.2 million of Due from affiliates, $1.7 million of Due from affiliates - less current portion, $11.3 million of Due to affiliates, and $0.1 million of Due to affiliates - less current portion was related to commodity contract assets and liabilities with Glencore. (2) Foreign exchange contracts reflect our outstanding FX swaps. The following table summarizes the net (loss) gain on forward and derivative contracts: Three months ended March 31, 2021 2020 Commodity contracts (1) $ (96.0) $ 9.0 Foreign exchange contracts (2.1) (5.2) Total $ (98.1) $ 3.8 (1) For the three months ended March 31, 2021 and 2020,

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On April 9, 2021, we completed our private offering of $86.3 million aggregate principal amount of the Convertible Notes. The Convertible Notes were issued at a price of 100% of their aggregate principal amount, will pay interest semi-annually in arrears on May 1 and November 1 of each year, beginning on November 1, 2021, at a rate of 2.75% per annum in cash, and will mature on May 1, 2028, unless earlier converted, repurchased or redeemed. The Convertible Notes are Century’s senior unsecured obligations and rank senior in right of payment to any of Century’s indebtedness that is expressly subordinated in right of payment to the Convertible Notes; equal in right of payment to any of Century’s unsecured indebtedness that is not so subordinated; effectively junior in right of payment to any of Century’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 Century’s subsidiaries. On April 14, 2021, we completed our offering of $250.0 million aggregate principal amount of the 2028 Notes. The 2028 Notes bear interest semi-annually in arrears on each April 1 and October 1 of each year, beginning on October 1, 2021, at a rate of 7.5% per year. Concurrently with the closing of the issuance of the 2028 Notes, on April 14, 2021, we accepted for purchase and purchased $195.9 million in aggregate principal amount of the 2025 Notes pursuant to a tender offer commenced in connection with the offering; and we notified the holders of all outstanding 2025 Notes that were not purchased in the tender offer of our election to redeem all such remaining 2025 Notes on May 14, 2021, and deposited with the trustee under the indenture governing the 2025 Notes an amount sufficient to fund the full redemption of the remaining 2025 Notes and discharge our obligations with respect thereto. We applied a portion of net proceeds from the offering of the 2028 Notes described above toward payment of the total consideration amount to holders whose 2025 Notes were accepted and purchased in the tender offer and the remaining proceeds from the issuance of the 2028 Notes and a portion of the net proceeds from the Convertible Notes will be used to fund the redemption of any remaining 2025 Notes, which will be redeemed on May 14, 2021. The remaining proceeds from the Convertible Notes offering were used to repay borrowings under our revolving credit facilities and to pay for the cost of the capped call transactions in connection with the issuance of the Convertible Notes. Based on the characteristics of the 2025 Notes and the 2028 Notes that were issued, the tender and redemption of the 2025 Notes would be accounted for as an extinguishment of the debt. Accordingly, we expect to record a loss on early extinguishment of debt in the second quarter of 2021, consisting of the write-off of deferred financing costs of $4.4 million and the debt discount of $2.2 million associated with the 2025 Notes, as well as the tender fees, including a tender premium of $14.6 million, paid as part of the tender offer. On April 16, 2021, a new, five-year collective bargaining agreement was ratified by the United Steelworkers Local 9423 for the Company's Hawesville, Kentucky smelter. The agreement will run through April 1, 2026.

General (Policies)

General (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards On January 1, 2021, we adopted Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." The ASU amendments include the removal of certain exceptions to the general principles of ASC 740 and to improve and simplify accounting for income taxes by clarifying and amending existing guidance. The adoption of the ASU did not have a material effect on the Company’s consolidated financial statements. On January 1, 2021, we adopted FASB ASU 2020-06, “Debt With Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity" using the modified retrospective method. The ASU amendments include simplification of the accounting models for convertible instruments and conversion options, and amendments to diluted earnings per share (“EPS”) calculations for certain convertible instruments, requiring the inclusion of convertible securities in the calculation of diluted EPS using the if-converted method. The adoption of the ASU did not have a material effect on the Company’s consolidated financial statements. On January 1, 2021, we adopted the final rule issued by the Securities and Exchange Commission (“SEC”) that amends the disclosure requirements related to issuers and guarantors of certain registered securities under SEC Regulation S-X Rule 3-10. We presented the alternative financial disclosures in Item 2 . Management's Discussion a n d A nalysis - Liquidity and Capital Resources . The adoption of the SEC rule is limited to disclosures only and did not have a material effect on the Company’s consolidated financial statements.

Related Party Transactions (Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Schedule of related party transactions	A summary of the aforementioned significant related party transactions is as follows: Three months ended March 31, 2021 2020 Net sales to Glencore $ 268.3 $ 271.0 Purchases from Glencore 72.3 40.2 .

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue Recognition and Deferred Revenue [Abstract]
Disaggregation of revenue	We disaggregate our revenue by geographical region as follows: Net Sales Three months ended March 31, 2021 2020 United States $ 276.2 $ 274.1 Iceland 167.8 147.1 Total $ 444.0 $ 421.2

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Financial assets and liabilities at fair value on a recurring basis	Recurring Fair Value Measurements As of March 31, 2021 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 13.3 $ — $ — $ 13.3 Trust assets (1) 1.5 — — 1.5 Derivative instruments — 14.8 0.0 14.8 TOTAL $ 14.8 $ 14.8 $ — $ 29.6 LIABILITIES: Contingent obligation – net $ — $ — $ — $ — Derivative instruments — 104.8 6.2 111.0 TOTAL $ — $ 104.8 $ 6.2 $ 111.0 Recurring Fair Value Measurements As of December 31, 2020 Level 1 Level 2 Level 3 Total ASSETS: Cash equivalents $ 54.2 $ — $ — $ 54.2 Trust assets (1) — — — — Derivative instruments — 12.1 3.0 15.1 TOTAL $ 54.2 $ 12.1 $ 3.0 $ 69.3 LIABILITIES: Contingent obligation – net $ — $ — $ — $ — Derivative instruments — 16.7 — 16.7 TOTAL $ — $ 16.7 $ — $ 16.7 (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 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 FX swaps Discounted cash flows Euro/USD forward exchange rate The following table presents the inputs for 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: Level 3 Fair Value Measurements: Asset / Liability Fair Value at March 31, 2021 Valuation Technique Observable Inputs Significant Unobservable Input Value/Range of Unobservable Input LME forward financial sales contracts $ (6.0) Discounted cash flows Quoted LME forward market Discount rate net (1) 10.00% Contingent obligation $ — Discounted cash flows Quoted LME forward market, management's estimate of the LME forward market prices for periods beyond the quoted periods, management's estimates of future level of operations Management's estimates of the LME forward market price beyond the quoted periods (2) $2,217/T-$2,321/T FX swaps $ (0.2) Discounted cash flows Euro/USD forward exchange rate Discount rate net (1) 10.00% (1) Represents risk adjusted discount rate. (2) Represents the range of estimated forward LME prices of primary aluminum through the term of the agreement in December 2028.
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. Level 3 Liabilities For the three months ended March 31, 2021 LME forward financial sales contracts FX Swaps Balance as of January 1, 2021 $ 2.9 $ 0.1 Total realized/unrealized gains (losses) Included in net income (loss) (1) (8.7) — Purchases, sales, settlements Purchases — — Sales — — Settlements — — Transfers into Level 3 (2) (0.7) (0.2) Transfers out of Level 3 (3) 0.5 (0.1) Balance as of March 31, 2021 (6.0) $ (0.2) Change in unrealized gains (losses) (1) $ (8.7) $ — (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 during the first quarter of 2021. (3) Transfers out of Level 3 due to period of time remaining in derivative contract. For the three months ended March 31, 2020 Level 3 Assets Level 3 Liabilities U.S. LME forward financial sales contracts Hawesville L4 Power Price Swaps Balance as of January 1, 2020 $ 10.6 $ (2.9) Total realized/unrealized gains (losses) Included in Net Income (1) 6.7 (1.5) Purchases, sales, settlements Purchases — — Sales — — Settlements — 1.2 Transfers into Level 3 (2) — — Transfers out of Level 3 (3) (9.5) — Balance as of March 31, 2020 $ 7.8 $ (3.2) Change in unrealized gains (losses) (1) $ 6.7 $ (0.3) (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 during the first quarter of 2020.

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Basic and diluted earnings (loss) per share	The following table shows the basic and diluted earnings (loss) per share: For the three months ended March 31 2021 2020 Net Income (Loss) Shares (in millions) Per Share Net Income (Loss) Shares (in millions) Per Share Net income (loss) $ (140.0) $ (2.7) Amount allocated to common stockholders 100.0 % 100.0 % Basic and diluted EPS (1) $ (140.0) 90.1 $ (1.55) $ (2.7) 89.3 $ (0.03) (1) In periods when we report a net loss, all share-based compensation awards and convertible preferred shares are excluded from the calculation of diluted weighted average shares outstanding because of their anti-dilutive effect on earnings (loss) per share.
Securities excluded from the calculation of diluted EPS	Three months ended March 31, Securities excluded from the calculation of diluted EPS (in millions) (1) : 2021 2020 Share-based compensation 2.2 0.4 Convertible preferred shares (2) 6.4 — (1) In periods when we report a net loss, all share-based compensation awards and convertible preferred shares are excluded from the calculation of diluted weighted average shares outstanding because of their anti-dilutive effect on earnings (loss) per share.

Shareholders_ Equity (Tables)

Shareholders’ Equity (Tables)	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity Note [Abstract]
Common and preferred stock activity	The Common and Preferred Stock table below contains additional information about preferred stock conversions during the three months ended March 31, 2021 and 2020. Preferred stock Common stock Common and Preferred Stock Activity (in shares): Series A Convertible Treasury Outstanding Beginning balance as of December 31, 2020 63,589 7,186,521 90,055,797 Conversion of convertible preferred stock (137) — 13,697 Issuance for share-based compensation plans — — 18,220 Ending balance as of March 31, 2021 63,452 7,186,521 90,087,714 Beginning balance as of December 31, 2019 67,323 7,186,521 89,185,661 Conversion of convertible preferred stock (1,182) — 118,146 Issuance for share-based compensation plans — — 157,158 Ending balance as of March 31, 2020 66,141 7,186,521 89,460,965

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory, Net [Abstract]
Schedule of inventories	Inventories consist of the following: March 31, 2021 December 31, 2020 Raw materials $ 105.2 $ 95.9 Work-in-process 44.1 40.5 Finished goods 22.7 26.9 Operating and other supplies 131.0 127.8 Total inventories $ 303.0 $ 291.1

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of debt	March 31, 2021 December 31, 2020 Debt classified as current liabilities: Hawesville Term Loan (1) $ 15.0 $ 20.0 Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) (2) 7.8 7.8 U.S. Revolving Credit Facility (3) 50.4 — Debt classified as non-current liabilities: Iceland Revolving Credit Facility (4) — 45.0 12.0% senior secured notes due July 1, 2025, net of debt discount of $2.2 million and $2.3 million, and financing fees of $4.4 million and $4.6 million at March 31, 2021 and December 31, 2020, respectively, interest payable semiannually 243.4 243.1 Total $ 316.6 $ 315.9 (1) See "Hawesville Term Loan" below. At March 31, 2021, the applicable interest rate was LIBOR of 0.2% plus margin of 5.375% and there is no interest payable outstanding. As of March 31, 2021, we have made $25.0 million of principal payments and $2.2 million of interest payments. (2) 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 IRBs interest rate at March 31, 2021 was 0.2%. (3) We have elected to incur interest at a base rate plus applicable margin as defined within the agreement. The interest rate at March 31, 2021 was 3.8%.
Schedule of line of credit facilities	Status of our U.S. revolving credit facility: March 31, 2021 Credit facility maximum amount $ 175.0 Borrowing availability 139.6 Outstanding letters of credit issued 75.4 Outstanding borrowings 50.4 Borrowing availability, net of outstanding letters of credit and borrowings 13.8 Status of our Iceland revolving credit facility: March 31, 2021 Credit facility maximum amount $ 50.0 Borrowing availability 50.0 Outstanding letters of credit issued — Outstanding borrowings — Borrowing availability, net of borrowings 50.0

Components of Accumulated Oth_2

Components of Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated balances for each component of AOCI	Components of AOCL: March 31, 2021 December 31, 2020 Defined benefit plan liabilities $ (122.3) $ (123.7) Unrealized gain (loss) on financial instruments 2.1 2.1 Other comprehensive loss before income tax effect (120.2) (121.6) Income tax effect (1) 2.7 2.8 Accumulated other comprehensive loss $ (117.5) $ (118.8) (1) The allocation of the income tax effect to the components of other comprehensive loss is as follows: March 31, 2021 December 31, 2020 Defined benefit plan liabilities $ 3.1 $ 3.2 Unrealized loss on financial instruments (0.4) (0.4) The following table summarizes the changes in the accumulated balances for each component of AOCL: Defined benefit plan and other postretirement liabilities Unrealized gain (loss) on financial instruments Total, net of tax Balance, January 1, 2021 $ (120.6) $ 1.8 $ (118.8) Net amount reclassified to net income (loss) 1.3 0.0 1.3 Balance, March 31, 2021 $ (119.3) $ 1.8 $ (117.5) Balance, January 1, 2020 $ (111.7) $ 1.9 $ (109.8) Net amount reclassified to net income 1.4 0.0 1.4 Balance, March 31, 2020 $ (110.3) $ 1.9 $ (108.4)
Reclassification out of AOCI	Reclassifications out of AOCL were included in the consolidated statements of operations as follows: Three months ended March 31, AOCL Components Location 2021 2020 Defined benefit plan and other postretirement liabilities Cost of goods sold $ 0.8 $ 1.1 Selling, general and administrative expenses 0.2 0.2 Other operating expense, net 0.4 0.4 Income tax effect (0.1) (0.3) Net of tax $ 1.3 $ 1.4 Unrealized loss on financial instruments Cost of goods sold $ 0.0 $ 0.0 Income tax effect 0.0 0.0 Net of tax $ 0.0 $ 0.0

Components of Net Periodic Be_2

Components of Net Periodic Benefit Cost (Tables)	3 Months Ended
	Mar. 31, 2021
Components of net periodic benefit cost [Abstract]
Schedule of net periodic benefit cost	Pension Benefits Three months ended March 31, 2021 2020 Service cost $ 1.4 $ 1.3 Interest cost 2.4 2.8 Expected return on plan assets (5.5) (5.1) Amortization of prior service costs 0.0 0.0 Amortization of net loss 1.5 1.5 Net periodic benefit cost $ (0.2) $ 0.5 Other Postretirement Benefits ("OPEB") Three months ended March 31, 2021 2020 Service cost $ 0.1 $ 0.1 Interest cost 0.6 0.8 Amortization of prior service cost (0.8) (0.8) Amortization of net loss 0.6 1.0 Net periodic benefit cost $ 0.5 $ 1.1

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives not designated as hedging instruments	The following table sets forth the Company's derivative assets and liabilities that were accounted for at fair value and not designated as cash flow hedges as of March 31, 2021 and December 31, 2020, respectively: Asset Fair Value March 31, 2021 December 31, 2020 Commodity contracts (1) $ 14.4 $ 12.8 Foreign exchange contracts (2) 0.4 2.4 Total $ 14.8 $ 15.2 Liability Fair Value March 31, 2021 December 31, 2020 Commodity contracts (1) $ 110.5 $ 16.7 Foreign exchange contracts (2) 0.5 — Total $ 111.0 $ 16.7 (1) Commodity contracts reflect our outstanding LME forward financial sales contracts, MWP forward financial sales contracts, fixed for floating swaps, and Nord Pool power price swaps. At March 31, 2021, $22.3 million of Due to affiliates and $6.5 million of Due to affiliates - less current portion was related to commodity contract liabilities with Glencore. At December 31, 2020, $1.2 million of Due from affiliates, $1.7 million of Due from affiliates - less current portion, $11.3 million of Due to affiliates, and $0.1 million of Due to affiliates - less current portion was related to commodity contract assets and liabilities with Glencore. (2) Foreign exchange contracts reflect our outstanding FX swaps.
Schedule of derivative instruments	The following table summarizes the net (loss) gain on forward and derivative contracts: Three months ended March 31, 2021 2020 Commodity contracts (1) $ (96.0) $ 9.0 Foreign exchange contracts (2.1) (5.2) Total $ (98.1) $ 3.8 (1) For the three months ended March 31, 2021 and 2020,

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Apr. 29, 2019
Related Party Transaction [Line Items]
Related parties	$ 268,300,000	$ 271,000,000
Glencore [Member]
Related Party Transaction [Line Items]
Related parties	268,300,000	271,000,000
Hawesville [Member]
Related Party Transaction [Line Items]
Term loan - less current portion			$ 40,000,000
Aluminum [Member] | Glencore [Member]
Related Party Transaction [Line Items]
Related parties	$ 0	$ 300,000
Consolidated Sales [Member] | Customer Concentration Risk [Member] | Glencore [Member]
Related Party Transaction [Line Items]
Major customer, percentage of revenue, net (percent)	60.00%	64.00%
Glencore [Member]
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners	42.90%
Economic ownership percentage by related party	46.70%

Related Party Transactions - Su

Related Party Transactions - Summary of related party transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Related Party Transaction [Line Items]
Net sales	$ 268.3	$ 271
Glencore [Member]
Related Party Transaction [Line Items]
Net sales	268.3	271
Purchases	$ 72.3	$ 40.2

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 444	$ 421.2
United States [Member]
Disaggregation of Revenue [Line Items]
Revenue	276.2	274.1
Iceland [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 167.8	$ 147.1

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ASSETS:
Cash equivalents	$ 13.3	$ 54.2
Trust assets	1.5	0
Derivative instruments	14.8	15.1
TOTAL	29.6	69.3
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0	0
Derivative instruments	111	16.7
TOTAL	111	16.7
Level 1 [Member]
ASSETS:
Cash equivalents	13.3	54.2
Trust assets	1.5	0
Derivative instruments	0	0
TOTAL	14.8	54.2
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0	0
Derivative instruments	0	0
TOTAL	0	0
Level 2 [Member]
ASSETS:
Cash equivalents	0	0
Trust assets	0	0
Derivative instruments	14.8	12.1
TOTAL	14.8	12.1
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0	0
Derivative instruments	104.8	16.7
TOTAL	104.8	16.7
Level 3 [Member]
ASSETS:
Cash equivalents	0	0
Trust assets	0	0
Derivative instruments	0	3
TOTAL	0	3
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0	0
Derivative instruments	6.2	0
TOTAL	$ 6.2	$ 0

Fair Value Measurements - Signi

Fair Value Measurements - Significant Unobservable Inputs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)MWhT	Dec. 31, 2020USD ($)
LME Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ (6)	$ 2.9
LME Swap [Member] | Discounted Cash Flow [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, percentage	0.1000
Contingent obligation [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 0
Contingent obligation [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset (in tones) | T	2,217
Contingent obligation [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset (in tones) | T	2,321
FX Swap [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ (0.2)	$ 0.1
FX Swap [Member] | Discounted Cash Flow [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability (in MwH) | MWh	0.1000

Fair Value Measurements - Level

Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
LME Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	$ 2.9
Total realized/unrealized gains (losses)
Included in net income (loss)	(8.7)
Purchases, sales, settlements
Purchases	0
Sales	0
Settlements	0
Transfers into Level 3	(0.7)
Transfers out of Level 3	0.5
Balance, ending	(6)
Change in unrealized gains (losses)	(8.7)
FX Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	0.1
Total realized/unrealized gains (losses)
Included in net income (loss)	0
Purchases, sales, settlements
Purchases	0
Sales	0
Settlements	0
Transfers into Level 3	(0.2)
Transfers out of Level 3	(0.1)
Balance, ending	(0.2)
Change in unrealized gains (losses)	$ 0
Hawesville L4 Power Price Swaps [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning		$ (2.9)
Total realized/unrealized gains (losses)
Included in net income (loss)		(1.5)
Purchases, sales, settlements
Purchases		0
Sales		0
Settlements		1.2
Transfers into Level 3		0
Transfers out of Level 3		0
Balance, ending		(3.2)
Change in unrealized gains (losses)		(0.3)
United States [Member] | LME Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning		10.6
Total realized/unrealized gains (losses)
Included in net income (loss)		6.7
Purchases, sales, settlements
Purchases		0
Sales		0
Settlements		0
Transfers into Level 3		0
Transfers out of Level 3		(9.5)
Balance, ending		7.8
Change in unrealized gains (losses)		$ 6.7

Earnings (Loss) Per Share (Deta

Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income (loss)	$ (140)	$ (2.7)
Amount allocated to common stockholders (as percent)	100.00%	100.00%
Basic and diluted EPS
Net income (loss) allocated to common stockholders (in shares)	90,100	89,300
Basic and diluted (in dollars per share)	$ (1.55)	$ (0.03)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	2,200	400
Series A Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (in shares)	6,400	0

Shareholders_ Equity (Details)

Shareholders’ Equity (Details) - USD ($)	3 Months Ended			72 Months Ended	123 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2015	Mar. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2011	Dec. 31, 2008
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	195,000,000			195,000,000	195,000,000	195,000,000
Common stock, par value (in dollars per share)	$ 0.01			$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	97,274,235			97,274,235	97,274,235	97,242,318
Common stock, shares, outstanding (in shares)	90,087,714			90,087,714	90,087,714	90,055,797
Preferred stock, shares authorized (in shares)	5,000,000			5,000,000	5,000,000	5,000,000
Preferred stock par value (in dollars per share)	$ 0.01			$ 0.01	$ 0.01	$ 0.01
Preferred shares issued (in shares)								160,000
Number of shares issued for each share of preferred stock (in shares)	100			100	100
Stock repurchase program, authorized amount			$ 130,000,000				$ 60,000,000
Stock repurchase program, authorized, increase amount			$ 70,000,000
Treasury stock, shares, acquired (in shares)				0	7,186,521
Treasury stock, value, acquired, cost method					$ 86,300,000
Stock repurchase program, remaining authorized repurchase amount	$ 43,700,000			$ 43,700,000	$ 43,700,000
Series A Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares outstanding (in shares)	63,452			63,452	63,452	63,589
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	63,589	67,323
Conversion of convertible preferred stock (in shares)	(137)	(1,182)
Issuance for share-based compensation plans (in shares)	0	0
Ending balance (in shares)	63,452	66,141		63,452	63,452
Treasury [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	7,186,521	7,186,521
Conversion of convertible preferred stock (in shares)	0	0
Issuance for share-based compensation plans (in shares)	0	0
Ending balance (in shares)	7,186,521	7,186,521		7,186,521	7,186,521
Common stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	90,055,797	89,185,661
Conversion of convertible preferred stock (in shares)	13,697	118,146
Issuance for share-based compensation plans (in shares)	18,220	157,158
Ending balance (in shares)	90,087,714	89,460,965		90,087,714	90,087,714

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income tax benefit	$ 2.3	$ 2.8

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Inventory, Net [Abstract]
Raw materials	$ 105.2	$ 95.9
Work-in-process	44.1	40.5
Finished goods	22.7	26.9
Operating and other supplies	131	127.8
Total inventories	$ 303	$ 291.1

Debt - Activity (Details)

Debt - Activity (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Jul. 01, 2020
Debt Instrument [Line Items]
Hawesville term loan - current portion	$ 15,000,000	$ 20,000,000
Hancock County industrial revenue bonds (IRBs) due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%))	7,800,000	7,800,000
Total debt	316,600,000	315,900,000
Long-term Debt [Member] | Revolving credit facility [Member] | Iceland revolving line of credit [Member]
Debt Instrument [Line Items]
Revolving credit facility	0	45,000,000
Long-term Debt [Member] | Senior Secured Notes Due June 01, 2025 [Member]
Debt Instrument [Line Items]
Senior securities notes	$ 243,400,000	243,100,000
Stated interest rate, percentage	12.00%		12.00%
Debt discount	$ 2,200,000	2,300,000
Financing fees	4,400,000	4,600,000
Short-term Debt [Member] | Industrial revenue bonds due April 1, 2028 [Member]
Debt Instrument [Line Items]
Hancock County industrial revenue bonds (IRBs) due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%))	$ 7,800,000	7,800,000
Stated interest rate, percentage	0.20%
Short-term Debt [Member] | Industrial revenue bonds due April 1, 2028 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Effective interest rate, maximum	12.00%
Short-term Debt [Member] | Revolving credit facility [Member]
Debt Instrument [Line Items]
Stated interest rate, percentage	5.375%
Interest payable outstanding	$ 0
Principal payment	25,000,000
Interest payable	$ 2,200,000
Short-term Debt [Member] | Revolving credit facility [Member] | Revolving Credit Facility, Portion Subject To LIBOR Rate [Member]
Debt Instrument [Line Items]
Stated interest rate, percentage	0.20%
Short-term Debt [Member] | Revolving credit facility [Member] | U.S. revolving credit facility [Member]
Debt Instrument [Line Items]
Revolving credit facility	$ 50,400,000	0
Stated interest rate, percentage	3.80%
Hawesville [Member] | Short-term Debt [Member]
Debt Instrument [Line Items]
Hawesville term loan - current portion	$ 15,000,000	$ 20,000,000

Debt - Narrative (Details)

Debt - Narrative (Details)	Apr. 09, 2021USD ($)	Jul. 01, 2020USD ($)	Apr. 29, 2019USD ($)payment	Apr. 14, 2021USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
U.S. revolving credit facility [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings					$ 50,400,000
Credit facility maximum amount					175,000,000
U.S. revolving credit facility [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount					175,000,000
U.S. letter of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount					110,000,000
U.S. revolving credit facility, accordion [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility face amount					50,000,000
Iceland revolving line of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings					0
Credit facility maximum amount					50,000,000
Senior Secured Notes Due June 01, 2025 [Member]
Line of Credit Facility [Line Items]
Proceeds from issuance of debt		$ 243,800,000
Debt instrument, tender premium					14,600,000
Senior Secured Notes Due June 01, 2025 [Member] | Level 2 [Member]
Line of Credit Facility [Line Items]
Fair value of debt instrument					$ 268,800,000
Senior Secured Notes Due June 01, 2025 [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Stated interest rate, percentage		12.00%			12.00%
Face amount		$ 250,000,000
Senior Secured Notes Due June 01, 2025 [Member] | Long-term Debt [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face amount				$ 250,000,000
Debt instrument, tender premium				$ 14,600,000
Interest rate, cash percentage				7.50%
Convertible Senior Note Due 2028 [Member] | Long-term Debt [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Face amount	$ 86,300,000
Interest rate, cash percentage	2.75%
Percentage of aggregate principal amount issued	100.00%
Revolving Credit Facility [Member] | Iceland revolving line of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Revolving credit facility					$ 0	$ 45,000,000
Senior Secured Notes Due 2028 [Member] | Long-term Debt [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Stated interest rate, percentage				7.50%
Face amount				$ 250,000,000
Debt instrument, repurchased face amount				$ 195,900,000
Hawesville [Member]
Line of Credit Facility [Line Items]
Due to related parties, noncurrent			$ 40,000,000
Debt instrument, payment terms, number of monthly payments | payment			24
London Interbank Offered Rate (LIBOR) [Member] | Hawesville [Member]
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate			5.375%

Debt - Credit Facility (Details

Debt - Credit Facility (Details)	Mar. 31, 2021USD ($)
U.S. revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount	$ 175,000,000
Borrowing availability	139,600,000
Outstanding letters of credit issued	75,400,000
Outstanding borrowings	50,400,000
Borrowing availability, net of borrowings	13,800,000
Iceland revolving line of credit [Member] | Long-term Debt [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount	50,000,000
Borrowing availability	50,000,000
Outstanding letters of credit issued	0
Outstanding borrowings	0
Borrowing availability, net of borrowings	$ 50,000,000

Commitments and Contingencies (

Commitments and Contingencies (Details)	Apr. 01, 2021	Aug. 18, 2017USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2021USD ($)Labor_UnionMW	Mar. 31, 2020USD ($)	Dec. 31, 2013USD ($)
Labor Commitments [Abstract]
Percentage of total work force in union				66.00%
Percentage of Grundartangi work force represented by the labor unions (in hundredths)				85.00%
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | Labor_Union				5
Percentage of U.S. based work force represented by a union (in hundredths)				58.00%
Ravenswood Retiree Medical Benefits Changes [Member]
Ravenswood litigation [Abstract]
Gain (loss) related to litigation settlement			$ 5,500,000
Loss contingency accrual			12,500,000
PBGC Agreement [Member]
PBGC Settlement [Abstract]
Required pension contributions above minimum						$ 17,400,000
Payment for pension benefits				$ 0	$ 0
Pension contributions above minimum remaining				$ 9,600,000
Hawesville [Member]
Power Contingencies [Abstract]
Power supply agreement, termination notice period				1 year
Sebree [Member]
Power Contingencies [Abstract]
Power supply agreement, termination notice period				1 year
Santee Cooper [Member] | Subsequent Event [Member]
Power Contingencies [Abstract]
Power agreement, power supply, percentage	100.00%
Power supply agreement, increase production, at full capacity, percentage	75.00%
Grundartangi - HS, Landsvirkjun and OR [Member]
Power Contingencies [Abstract]
Power currently available under the power purchase agreement (in megawatts) | MW				525
Grundartangi - Landsvirkjun [Member]
Power Contingencies [Abstract]
Power currently available under the power purchase agreement (in megawatts) | MW				161
Helguvik [Member]
Power Contingencies [Abstract]
Power currently available under the power purchase agreement (in megawatts) | MW				47.5
Netherlands [Member]
Labor Commitments [Abstract]
Percentage of Vlissingen work force represented by the labor union (in hundredths)				100.00%
Ravenswood Retiree Medical Benefits Changes [Member]
Ravenswood litigation [Abstract]
Ravenswood litigation settlement amount		$ 23,000,000
Ravenswood litigation settlement installment period		10 years		9 years
Litigation payment to trust			$ 5,000,000
Litigation settlement, amount awarded to other party, annual payments				$ 2,000,000
Other Current Liabilities [Member] | Ravenswood Retiree Medical Benefits Changes [Member]
Ravenswood litigation [Abstract]
Litigation settlement, amount awarded to other party, annual payments				2,000,000
Other Liabilities [Member] | Ravenswood Retiree Medical Benefits Changes [Member]
Ravenswood litigation [Abstract]
Litigation settlement, amount awarded to other party, annual payments				$ 7,700,000

Components of Accumulated Oth_3

Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	$ (120.2)		$ (121.6)
Income tax effect	2.7		2.8
Accumulated other comprehensive loss	(117.5)		(118.8)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	546.1	$ 675
Net amount reclassified to net income (loss)	1.3	1.4
Balance, end	408.3	673.8
Defined benefit plan and other postretirement liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	(122.3)		(123.7)
Income tax effect	3.1		3.2
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(120.6)	(111.7)
Net amount reclassified to net income (loss)	1.3	1.4
Balance, end	(119.3)	(110.3)
Unrealized gain (loss) on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	2.1		2.1
Income tax effect	(0.4)		$ (0.4)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	1.8	1.9
Net amount reclassified to net income (loss)	0	0
Balance, end	1.8	1.9
Accumulated other comprehensive loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, start	(118.8)	(109.8)
Balance, end	$ (117.5)	$ (108.4)

Components of Accumulated Oth_4

Components of Accumulated Other Comprehensive Loss - Reclassifications out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	$ 464.7	$ 416.4
Selling, general and administrative expenses	16.1	8.9
Other operating (income) expense - net	0.1	0.3
Income tax effect	(2.3)	(2.8)
Net of tax	140	2.7
Reclassification out of accumulated other comprehensive income [Member] | Defined benefit plan and other postretirement liabilities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	0.8	1.1
Selling, general and administrative expenses	0.2	0.2
Other operating (income) expense - net	0.4	0.4
Income tax effect	(0.1)	(0.3)
Net of tax	1.3	1.4
Reclassification out of accumulated other comprehensive income [Member] | Unrealized loss on financial instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of goods sold	0	0
Income tax effect	0	0
Net of tax	$ 0	$ 0

Components of Net Periodic Be_3

Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1.4	$ 1.3
Interest cost	2.4	2.8
Expected return on plan assets	(5.5)	(5.1)
Amortization of prior service costs	0	0
Amortization of net loss	1.5	1.5
Net periodic benefit cost	(0.2)	0.5
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.1	0.1
Interest cost	0.6	0.8
Amortization of prior service costs	(0.8)	(0.8)
Amortization of net loss	0.6	1
Net periodic benefit cost	$ 0.5	$ 1.1

Derivatives (Details)

Derivatives (Details) € in Millions	3 Months Ended
	Mar. 31, 2021EUR (€)MWht
LME Swap [Member]
Derivative [Line Items]
Other forward delivery contracts to sell primary aluminum, open (in tonnes)	175,716
Midwest Premium (MWP) [Member]
Derivative [Line Items]
Open position to offset fixed prices	418,500
Fixed For Floating Swaps [Member]
Derivative [Line Items]
Open position to offset fixed prices	16,482
Nordpool Power Price Swap [Member] | Grundartangi [Member]
Derivative [Line Items]
Power available | MWh	1,815,075
FX Swap [Member]
Derivative [Line Items]
Derivative asset | €	€ 42.2

Derivatives - Assets and Liabil

Derivatives - Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Due to affiliate, current	$ 39.7	$ 21.7
Due to affiliate, noncurrent	6.5	0.1
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative asset	14.8	15.2
Derivative liability	111	16.7
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative asset	14.4	12.8
Derivative liability	110.5	16.7
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative asset	0.4	2.4
Derivative liability	0.5	0
Glencore [Member] | Commodity Contract [Member]
Derivative [Line Items]
Due to affiliate, current	22.3	11.3
Due to affiliate, noncurrent	$ 6.5	0.1
Due from affiliate, current		1.2
Due from affiliate, noncurrent		$ 1.7

Derivatives - Net Gain (Loss) (

Derivatives - Net Gain (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	$ (98.1)	$ 3.8
Commodity Contract [Member]
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	(96)	9
Commodity Contract [Member] | Glencore [Member]
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	(20.3)	12.6
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, (loss) gain on derivative, net	$ (2.1)	$ (5.2)

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Apr. 16, 2021	Apr. 14, 2021	Apr. 09, 2021	Mar. 31, 2021	Dec. 31, 2020	Jul. 01, 2020
Subsequent Event [Member]
Subsequent Event [Line Items]
Collective bargaining agreement, term	5 years
Senior Secured Notes Due June 01, 2025 [Member]
Subsequent Event [Line Items]
Debt instrument, tender premium				$ 14,600,000
Long-term Debt [Member] | Convertible Senior Note Due 2028 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Face amount			$ 86,300,000
Percentage of aggregate principal amount issued			100.00%
Interest rate, cash percentage			2.75%
Long-term Debt [Member] | Senior Secured Notes Due 2028 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Face amount		$ 250,000,000
Stated interest rate, percentage		7.50%
Debt instrument, repurchased face amount		$ 195,900,000
Long-term Debt [Member] | Senior Secured Notes Due June 01, 2025 [Member]
Subsequent Event [Line Items]
Face amount						$ 250,000,000
Stated interest rate, percentage				12.00%		12.00%
Debt discount				$ 2,200,000	$ 2,300,000
Long-term Debt [Member] | Senior Secured Notes Due June 01, 2025 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Face amount		$ 250,000,000
Interest rate, cash percentage		7.50%
Write off of deferred financing cost		$ 4,400,000
Debt discount		2,200,000
Debt instrument, tender premium		$ 14,600,000