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Pension and Other Postretirement Benefits
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Pension and Other Postretirement Benefits Pension and Other Postretirement Benefits 
Pension Benefits
We maintain noncontributory defined benefit pension plans for certain foreign and domestic hourly and salaried employees. For the eligible domestic salaried employees, plan benefits are based primarily on years of service and average compensation during the later years of employment. For hourly employees, plan benefits are based primarily on a formula that provides a specific benefit for each year of service. Plan benefits are available to all permanent foreign employees. Our funding policy is to contribute amounts based upon actuarial and economic assumptions designed to achieve adequate funding of the projected benefit obligations and to meet the minimum funding requirements of the Employee Retirement Income Security Act of 1974 ("ERISA"). In addition, we maintain the supplemental executive retirement benefit ("SERB") plan for certain current and former executive officers, which is frozen to future accruals.
Other Postretirement Benefits ("OPEB")
In addition to providing pension benefits, we provide certain healthcare and life insurance benefits for certain foreign and domestic retired employees. We accrue the estimated cost of providing postretirement benefits during the working careers of those employees who could become eligible for such benefits when they retire. We fund these benefits as the retirees submit claims.
Retiree medical welfare changes
Under the current Hawesville labor agreement, employees who retire during the term of the labor agreement have been divided into sub-groups based on attributes such as Medicare eligibility, hire date, age and years of service. Levels of benefits are defined for the sub-groups and range from no substantive change from the benefits provided under the previous labor agreement to replacement of the defined retiree medical benefit program with individual health reimbursement accounts for each eligible participant. The health reimbursement accounts are funded based on established rates per hour worked by each eligible participant. Eligible participants will be able to withdraw from their health reimbursement accounts to fund their own retiree medical coverage.
During 2017, the Company amended its non-union retiree medical and life insurance benefits to align the Company’s benefits with the market and achieve a uniform retiree medical benefit design across the Company’s U.S. locations. Effective January 1, 2018, non-union retiree medical and life insurance benefits are restricted to current participants who meet the eligibility criteria as of January 1, 2018. Additionally, effective January 1, 2019, Century no longer administers non-union retiree medical, prescription drug, dental, or vision benefits and instead makes fixed health reimbursement account contributions.
Obligation and Funded Status
The change in benefit obligation and change in plan assets as of December 31 are as follows:
PensionOPEB
2024202320242023
Change in benefit obligation:    
Benefit obligation at beginning of year$305.1 $263.0 $76.8 $73.7 
Service cost4.0 3.3 0.2 0.1 
Interest cost17.2 17.3 3.9 3.9 
Plan amendments— 1.1 — — 
Actuarial (gain) loss(3.2)11.0 0.3 4.8 
Medicare Part D— — 0.2 0.3 
Acquisition— 28.6 — 0.8 
Benefits paid(21.4)(19.9)(5.7)(6.8)
Exchange rates(0.4)(0.5)— — 
Plan participants' contributions1.0 1.2 — — 
Benefit obligation at end of year$302.3 $305.1 $75.7 $76.8 
The decreases in both the defined benefit plans' and OPEB plans' benefit obligation were mainly driven by lower interest costs and actuarial gains in 2024, which were primarily attributable to the changes in the discount rates from fiscal year 2023 to 2024.
PensionOPEB
2024202320242023
Change in plan assets:    
Fair value of plan assets at beginning of year$256.8 $216.6 $— $— 
Actual return on plan assets6.8 21.4 — — 
Acquisition— 31.5 — — 
Employer contributions2.3 6.6 5.5 6.5 
Medicare Part D subsidy received— — 0.2 0.3 
Benefits paid(21.5)(19.9)(5.7)(6.8)
Exchange rates(0.3)(0.6)— — 
Plan participants' contributions1.0 1.2 — 
Fair value of assets at end of year$245.1 $256.8 $— $— 
The change in actual return on plan assets in 2024 was primarily attributable to fluctuations in market prices during the year.
 PensionOPEB
 2024202320242023
Funded status of plans:    
Funded status$(57.2)$(48.3)$(75.7)$(76.8)
Amounts recognized in the Consolidated Balance Sheets:
Current liabilities(1.8)(1.8)(6.5)(6.5)
Non-current liabilities(55.4)(46.5)(69.2)(70.3)
Net amount recognized$(57.2)$(48.3)$(75.7)$(76.8)
Amounts recognized in accumulated other comprehensive loss (pre-tax):  
Net loss$82.3 $82.1 $14.4 $14.8 
Prior service cost (benefit)1.6 1.8 — — 
Total$83.9 $83.9 $14.4 $14.8 
Pension Plans That Are Not Fully Funded
At December 31, 2024, the projected benefit obligation, accumulated benefit obligation and fair value of plan assets for the pension plans with accumulated benefit obligations in excess of plan assets were $302.3 million, $279.3 million, and $245.1 million, respectively.
At December 31, 2023, the projected benefit obligation, accumulated benefit obligation and fair value of plan assets for the pension plans with accumulated benefit obligations in excess of plan assets were $305.1 million, $305.9 million and $256.8 million, respectively.
Components of net periodic benefit cost and other amounts recognized in other comprehensive income (loss):
Net Periodic Benefit Cost:
 Year Ended December 31,
 PensionOPEB
 202420232022202420232022
Service cost$4.0 $3.3 $4.3 $0.2 $0.1 $0.2 
Interest cost17.2 17.3 10.3 3.9 3.9 2.9 
Expected return on plan assets(18.3)(17.3)(23.5)— — — 
Amortization of prior service costs0.2 0.1 0.1 — — (1.3)
Amortization of net loss5.8 6.0 3.5 0.7 0.1 1.3 
Net periodic benefit cost8.9 9.4 (5.3)4.8 4.1 3.1 
Curtailment benefit (1)
— — — — — (8.9)
Total benefit cost$8.9 $9.4 $(5.3)$4.8 $4.1 $(5.8)
(1)During 2022, we re-measured certain other postretirement benefits triggered by the Hawesville smelter curtailment, leading to a non-cash OPEB curtailment benefit totaling $8.9 million for the year ended December 31, 2022.
Other changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (pre-tax):
 Year Ended December 31,
 PensionOPEB
 2024202320242023
Net (gain) loss$8.4 $6.9 $0.3 $4.8 
Net loss (gain) transferred due to acquisition— (4.5)— (0.2)
Prior service cost (benefit)— 1.2 — — 
Amortization of net loss, including recognition due to settlement(5.8)(6.0)(0.7)(0.2)
Amortization of prior service (cost) benefit, including curtailment(0.2)(0.1)— — 
Exchange rates(2.4)(1.1)— (0.1)
Total amount recognized in other comprehensive income (loss)
— (3.6)(0.4)4.3 
Net periodic benefit cost8.9 9.4 4.8 4.1 
Total recognized in net periodic benefit cost and other comprehensive income (loss)
$8.9 $5.8 $4.4 $8.4 
Weighted average assumptions used to determine benefit obligations at December 31:
PensionOPEB
2024202320242023
Discount rate (1)
5.99%5.19%5.62%5.19%
Rate of compensation increase without Jamaica3.0%3.5%3.0%3.5%
Rate of compensation increase Jamaica7.0%n/a7.0%n/a
Measurement date12/31/202412/31/202312/31/202412/31/2023
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
 PensionOPEB
 202420232022202420232022
Measurement date12/31/202312/31/202212/31/202112/31/202312/31/202212/31/2021
Fiscal year end12/31/202412/31/202312/31/202212/31/202412/31/202312/31/2022
Discount rate (1)
6.75%5.50%2.94%5.43%5.57%2.64%
Rate of compensation increase without Jamaica (2)
3.5%
4%/3.5%
3%/3.5%
3.5%
4%/3.5%
3%/3.5%
Rate of compensation increase Jamaica9.0%n/an/a8.0%n/an/a
Expected return on plan assets (3)
7.28%7.25%7.25%—%—%—%
(1)We use the Ryan Above Median Yield Curve to determine the discount rate.
(2)For 2024, the rate of compensation increase is 3.5%. For 2023, the rate of compensation increase was 4% per year for the first year and 3.5% per year thereafter. For 2022, the rate of compensation increase was 3% per year for the first year and 3.5% per year thereafter.
(3)The rate for each of our defined benefit plans was selected by taking into account our expected asset mix and is based on historical performance as well as expected future rates of return on plan assets.
For measurement purposes, medical cost inflation for location other than Jamaica is initially estimated to be 8.5%, and 7.5% for pre- and post-65 participants, respectively, declining to 4.5% over ten years and continuing thereafter. For Jamaica, it is initially estimated to be 8.0% for both pre and post 65 participants and for the next two years.
Benefit Plan Assets
Pension Plan Investment Strategy and Policy
The Pension Plans’ assets are invested in a prudent manner for the exclusive purpose of providing benefits to participants.
Other objectives are to:
•Provide a total return that, over the long term, provides sufficient assets to fund the pension plan liabilities subject to a level of risk, contributions and pension expense deemed appropriate by the company.
•Minimize, where possible, pension expense volatility, and inclusion of liability driven investing as an investment strategy when appropriate. As the funding ratio improves, the objectives will evolve to minimize the funded status volatility.
•Diversify investments within asset classes to reduce the impact of losses in single investments.
The assets of the Pension Plans are invested in compliance with ERISA, as amended, and any subsequent applicable regulations and laws.
Performance
Our performance objective is to outperform the return of weighing passive investment alternatives by the policy target allocations after fees at a comparable level of risk. This investment objective is expected to be achieved over the long term and is measured over rolling multi-year periods. Peer-relative performance comparisons will also be considered especially when performance deviates meaningfully from market indexes. Investment objectives for each asset class are included below.
Asset Allocation Policy
Asset allocation policy is the principal method for achieving the Pension Plans' investment objectives stated above. The Pension Plans’ weighted average long-term strategic asset allocation policy targets are as follows:
 Pension Plan Asset Allocation
 2024 TargetDecember 31, 2024December 31, 2023
Return seeking assets:
Global equity50%51%44%
Diversified credit15%17%15%
Real assets10%11%10%
Liability hedging assets25%20%28%
Cash—%1%3%
 100%100%100%
Global equities are held for their long-term expected return premium over fixed income investments and inflation. Fixed income is held for diversification relative to equities, and as a hedging instrument to interest rate volatility for the pension obligation. Diversified Credit and Real Assets are held for diversification relative to equities and for income generation.
The strategic role of global equities is to:
•Provide higher expected returns of the major asset classes.
•Maintain a diversified exposure within global stock markets through the use of multi-manager portfolio strategies.
The strategic role of fixed income is to:
•Diversify the Pension Plans’ equity exposure by investing in fixed income securities that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio.
•Maintain a diversified exposure within the U.S. fixed income market through the use of portfolio strategies targeting treasury bond exposures.
•Hedge the interest rate risk of the pension obligation by investing in securities that target a similar duration to the pension obligation cash flows.
The strategic role of diversified credit is to:
•Diversify the Pension Plans’ equity exposure by investing in alternative credit securities that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio.
•Maintain a diversified exposure within the alternative credit markets through the use of multi-manager portfolio strategies targeting, but not limited to, securitized credit, high yield securities, and emerging market debt.
•Achieve returns in excess of passive indexes through the use of active investment managers and strategies.
The strategic role of real assets is to:
•Diversify the Pension Plans’ equity exposure by investing in real assets that exhibit a low correlation to equities, thereby lowering the overall return volatility of the entire investment portfolio.
•Maintain a diversified exposure within the real asset markets through the use of multi-manager portfolio strategies targeting listed and unlisted exposures.
•Achieve returns in excess of passive indexes through the use of active investment managers and strategies.
The long-term strategic asset allocation policy is reviewed regularly or whenever significant changes occur to Century’s or the Pension Plans' financial position and liabilities.
Fair Value Measurements of Pension Plan assets
The following table sets forth by level the fair value hierarchy our Pension Plans' assets. These assets are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and the placement within the fair value hierarchy levels.
As more fully described within Note 7. Fair Value Measurements, the Company uses a three-level fair value hierarchy that prioritizes the inputs used to measure fair values. The fair value hierarchy provides transparency regarding the inputs we use to measure fair value. We categorize each fair value measurement in its entirety into the following three levels, based on the lowest level input that is significant to the entire measurement:
•Level 1 Inputs – quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date.
•Level 2 Inputs – inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.
•Level 3 Inputs – unobservable inputs for the asset or liability.
The following summarizes the Company’s Pension Plans' assets fair value by asset category:
As of December 31, 2024
Level 1Level 2Level 3Assets measured at NAVTotal
Cash and cash equivalents$0.7 $— $— $2.8 $3.5 
Global Equity20.0 — — 108.1 128.1 
Diversified Credit11.8 — — 35.3 47.1 
Real Assets— — — 23.1 23.1 
Liability hedging assets— — — 42.6 42.6 
Other
0.1 0.6 — — 0.7 
Total plan assets fair value$32.6 $0.6 $— $211.9 $245.1 
As of December 31, 2023
Cash and cash equivalents$0.4 $— $— $4.6 $5 
Global Equity19.7 — — 100.0 119.7 
Diversified Credit11.2 — — 34.7 45.9 
Real Assets— — — 22.8 22.8 
Liability hedging assets— — — 62.7 62.7 
Other
0.1 0.6 — — 0.7 
Total plan assets fair value$31.4 $0.6 $— $224.8 $256.8 
Our domestic Pension Plans’ assets are held in certain commingled funds and group trusts which do not have publicly quoted prices. The fair value of the commingled funds and group trusts is based on NAV of the underlying investments. The fair value of the underlying investments held by the commingled funds, separate accounts and common collective trusts is generally based on quoted prices in active markets. Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value. Our foreign plan assets are held in bonds and equity securities which have publicly quoted prices.
Our other postretirement benefit plans are unfunded. We fund these benefits as the retirees submit claims.
Pension and OPEB Cash Flows
During 2024 and 2023, we made contributions of approximately $2.3 million and $6.6 million, respectively, to the qualified defined benefit and SERB plans we sponsor and $5.5 million and $6.5 million, respectively, to the other postretirement benefit plans.
We expect to make the following contributions for 2025:
2025
Expected pension plan contributions$8.0 
Expected OPEB benefits payments6.4 
Estimated Future Benefit Payments
The following table provides the estimated future benefit payments for the pension and other postretirement benefit plans:
 Pension BenefitsOPEB Benefits
2025$20.5 $6.5 
202620.9 6.5 
202720.9 6.5 
202821.4 6.7 
202921.7 6.5 
2030 – 203494.8 30.9 
Participation in Multi-employer Pension Plans
The union-represented employees at Hawesville are part of a United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union ("USWA") sponsored multi-employer plan. Our contributions to the plan are determined at a fixed rate per hour worked. Currently, we do not have any plans to withdraw from or curtail participation in this plan. The risks of participating in a multi-employer plan are different from single-employer plans in the following respects:
•Assets contributed to the multi-employer plan by one employer may be used to provide benefits to employees of other participating employers.
•If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers.
•If a participating employer chooses to stop participating in a multi-employer plan, the employer may be required to pay the plan an amount based on the underfunded status of the plan, referred to as a withdrawal liability.
Century’s participation in the plan for the year ended December 31, 2024, is outlined in the table below.
FundSteelworkers Pension Trust
EIN / PN23-6648508 / 499
Pension Protection Act Zone Status 2023 (1)
 Green
Pension Protection Act Zone Status 2022 (1)
 Green
Subject to Financial Improvement/Rehabilitation Plan (2)
 No
Contributions of Century Aluminum 2024$0.04
Contributions of Century Aluminum 2023$0.2
Contributions of Century Aluminum 2022$1.6
Withdrawal from Plan ProbableNo
Surcharge Imposed No
Expiration Date of Collective Bargaining Agreement (2)
March 31, 2026
(1)The most recent Pension Protection Act zone status available in 2024 and 2023 is for the plan's year-end December 31, 2023 and December 31, 2022, respectively. The zone status is based on information that Century received from the plan as well as publicly available information per the Department of Labor and is certified by the plan’s actuary. Among other factors, plans in the green zone are at least 80 percent funded.
(2)The “Subject to Financial Improvement / Rehabilitation Plan” column indicates plans for which a financial improvement plan (FIP) or a rehabilitation plan (RP) is either pending or has been implemented. The last column lists the expiration date(s) of the collective-bargaining agreement(s) to which the plans are subject.

Century's contributions to the above plan is not 5% or more of the total contributions to the plan.
Century 401(k) Plans
We sponsor a tax-deferred savings plan under which eligible domestic employees may elect to contribute specified percentages of their compensation with Century. We match a portion of participants' contributions to the savings plan. Employee and matching contributions are considered fully vested immediately upon participation in the plan. Concurrent with the 2014 amendment to the Salaried Pension Plan that eliminated future accruals for participants who are under age 50 as of January 1, 2015 and closed the plan to new entrants, the Company increased the proportional match of contributions made to those affected by the amendment. The expense related to the plan was $6.3 million, $5.8 million, and $6.0 million for 2024, 2023, and 2022, respectively.