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Employee Benefits (Tables) | 12 Months Ended
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Dec. 31, 2023
Retirement Benefits [Abstract] |
Schedule of Assumptions Used for Benefit Obligation | Key Assumptions. The following table presents the weighted average assumptions used to determine benefit obligations:
|  | Pension Plans 1 |  |  | OPEB |  |  | Salaried VEBA |
|  | As of December 31, |  |  | As of December 31, |  |  | As of December 31, |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Discount rate |  |  | 4.95 | % |  |  | 5.16 | % |  |  | 4.92 | % |  |  | 5.14 | % |  |  | 4.89 | % |  |  | 5.10 | %
Rate of compensation increase |  |  | 2.63 | % |  |  | 2.69 | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | — | %
1. Assumptions for our pension plans are weighted based on the total benefit obligations of each.
Schedule of Assumptions Used to Determine Net Periodic Benefit Cost (Income) | The following table presents the weighted average assumptions used to determine net periodic postretirement benefit cost:
|  | Pension Plans 1 |  |  | OPEB |  |  | Salaried VEBA |
|  | Year Ended December 31, |  |  | Year Ended December 31, |  |  | Year Ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |  |  | 2023 |  |  | 2022 |  |  | 2021 |  |  | 2023 |  |  | 2022 |  |  | 2021 |
Discount rate |  |  | 5.19 | % |  |  | 2.90 | % |  |  | 2.89 | % |  |  | 5.14 | % |  |  | 2.64 | % |  |  | 2.97 | % |  |  | 5.10 | % |  |  | 2.49 | % |  |  | 2.05 | %
Expected long-term return on plan assets 2 |  |  | 6.33 | % |  |  | 6.02 | % |  |  | 5.78 | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | 5.75 | % |  |  | 5.50 | % |  |  | 5.50 | %
Rate of compensation increase |  |  | 2.63 | % |  |  | 2.69 | % |  |  | 2.74 | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | — | % |  |  | — | %
1. Assumptions for our pension plans are weighted based on the total benefit obligations of each. 2. The expected long-term rate of return assumption for the Salaried VEBA is based on the targeted investment portfolios provided to us by the trustee of the Salaried VEBA.
Schedule of Changes in Benefit Obligations | The following table presents the benefit obligations and funded status of our pension plans, OPEB, and the Salaried VEBA and the corresponding amounts that are included in our Consolidated Balance Sheets (in millions of dollars):
|  | Pension Plans |  |  | OPEB |  |  | Salaried VEBA |
|  | As of December 31, |  |  | As of December 31, |  |  | As of December 31, |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Change in benefit obligation: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Obligation at beginning of year |  | $ | 18.8 |  |  | $ | 20.3 |  |  | $ | 66.4 |  |  | $ | 83.5 |  |  | $ | 58.9 |  |  | $ | 79.8 |
Foreign currency translation adjustment |  |  | 0.2 |  |  |  | (0.5 | ) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Service cost |  |  | 3.8 |  |  |  | 5.8 |  |  |  | 1.1 |  |  |  | 1.6 |  |  |  | — |  |  |  | 0.1 |
Interest cost |  |  | 1.3 |  |  |  | 0.6 |  |  |  | 3.4 |  |  |  | 2.2 |  |  |  | 2.9 |  |  |  | 1.9 |
Prior service cost (credit)1 |  |  | 6.6 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | (8.8 | ) |  |  | — |
Actuarial loss (gain)2 |  |  | 0.2 |  |  |  | (7.1 | ) |  |  | (0.7 | ) |  |  | (20.4 | ) |  |  | 0.4 |  |  |  | (16.3 | )
Plan participants contributions |  |  | 0.1 |  |  |  | 0.1 |  |  |  | 0.1 |  |  |  | 0.1 |  |  |  | — |  |  |  | — |
Benefits paid |  |  | (0.5 | ) |  |  | (0.4 | ) |  |  | (1.5 | ) |  |  | (0.6 | ) |  |  | (6.5 | ) |  |  | (6.6 | )
Obligation at end of year 3 |  |  | 30.5 |  |  |  | 18.8 |  |  |  | 68.8 |  |  |  | 66.4 |  |  |  | 46.9 |  |  |  | 58.9 |
Change in plan assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair market value of plan assets at beginning of year |  |  | 14.9 |  |  |  | 9.8 |  |  |  | — |  |  |  | — |  |  |  | 42.4 |  |  |  | 59.2 |
Foreign currency translation adjustment |  |  | 0.2 |  |  |  | (0.5 | ) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Actual return on assets |  |  | 1.4 |  |  |  | (2.6 | ) |  |  | — |  |  |  | — |  |  |  | 6.1 |  |  |  | (10.2 | )
Plan participants contributions |  |  | 0.1 |  |  |  | 0.1 |  |  |  | 0.1 |  |  |  | 0.1 |  |  |  | — |  |  |  | — |
Company contributions |  |  | 4.4 |  |  |  | 8.5 |  |  |  | 1.4 |  |  |  | 0.5 |  |  |  | 1.1 |  |  |  | — |
Benefits paid |  |  | (0.5 | ) |  |  | (0.4 | ) |  |  | (1.5 | ) |  |  | (0.6 | ) |  |  | (6.5 | ) |  |  | (6.6 | )
Fair market value of plan assets at end of year |  |  | 20.5 |  |  |  | 14.9 |  |  |  | — |  |  |  | — |  |  |  | 43.1 |  |  |  | 42.4 |
Net funded status 4 |  | $ | (10.0 | ) |  | $ | (3.9 | ) |  | $ | (68.8 | ) |  | $ | (66.4 | ) |  | $ | (3.8 | ) |  | $ | (16.5 | )
Cumulative gain (loss) recognized in Accumulated other comprehensive income: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated net actuarial gain |  | $ | 1.3 |  |  | $ | 2.6 |  |  | $ | 17.4 |  |  | $ | 17.8 |  |  | $ | 5.2 |  |  | $ | 1.7 |
Prior service cost |  |  | (6.1 | ) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | (16.0 | ) |  |  | (29.7 | )
Total |  | $ | (4.8 | ) |  | $ | 2.6 |  |  | $ | 17.4 |  |  | $ | 17.8 |  |  | $ | (10.8 | ) |  | $ | (28.0 | )
1. The prior service cost relating to our pension plans in 2023 resulted from a new four-year collective bargaining agreement with the USW Local 104. In connection with the agreement, we amended the Kaiser Aluminum Warrick pension plan to increase certain pension benefits for covered plan participants, resulting in a $6.6 million pre-tax prior service cost, which we recorded in AOCI and amortize on a straight-line basis over approximately 10 years. The prior service credit relating to the Salaried VEBA in 2023 resulted from a decrease in the annual healthcare reimbursement benefit for plan participants. 2. The actuarial loss relating to our pension plans in 2023 was comprised of a $0.5 million loss due to a change in the discount rate and a $0.3 million gain due to changes in census information. The actuarial gain relating to our pension plans in 2022 was comprised of an $8.0 million gain due to a change in the discount rate and a $0.9 million loss due to changes in census information. The actuarial gain relating to the OPEB in 2023 was comprised of a $2.7 million gain due to a change in the projected depletion year, a $2.5 million gain due to changes in census information, a $3.1 million loss due to a change in the trend rate assumption, and a $1.4 million loss due to a change in the discount rate. The actuarial gain relating to the OPEB in 2022 was comprised of a $20.4 million gain due to a change in the discount rate, a $0.7 million gain due to changes in census information and a $0.7 million loss due to a change in the trend rate assumption. The actuarial loss relating to the Salaried VEBA in 2023 was comprised of a $0.7 million loss due to a change in the discount rate and a $0.3 million gain due to changes in census information. The actuarial gain relating to the Salaried VEBA in 2022 was comprised of a $12.6 million gain due to a change in the discount rate, a $2.6 million gain due to changes in census information and a $1.1 million gain due to a change in the trend rate assumption. 3. For the pension plans, the benefit obligation is the projected benefit obligation. For the Salaried VEBA and OPEB, the benefit obligation is the APBO. 4. At December 31, 2023, Net funded status relating to the pension plans consisted of $1.3 million within Other assets and $11.3 million within Pension and other postretirement benefits on our Consolidated Balance Sheets. At December 31, 2022, Net funded status relating to the pension plans consisted of $1.0 million within Other assets and $4.9 million within Pension and other postretirement benefits on our Consolidated Balance Sheets. Of the Net funded status relating to the OPEB at December 31, 2023, $3.3 million was included within Accrued salaries, wages and related expenses and $65.5 million was included within Pension and other postretirement benefits on our Consolidated Balance Sheets. Of the Net funded status relating to the OPEB at December 31, 2022, $2.0 million was included within Accrued salaries, wages and related expenses and $64.4 million was included within Pension and other postretirement benefits on our Consolidated Balance Sheets. Net funded status relating to the Salaried VEBA at December 31, 2023 and December 31, 2022 was included within Net liabilities of Salaried VEBA on our Consolidated Balance Sheets.
Schedule of Expected Benefit Payments | The following table presents the net benefits expected to be paid (in millions of dollars):
|  | Year Ended December 31, |
|  | 2024 |  |  | 2025 |  |  | 2026 |  |  | 2027 |  |  | 2028 |  |  | 2029-2033 |
Pension benefit payments |  | $ | 0.8 |  |  | $ | 1.0 |  |  | $ | 1.2 |  |  | $ | 1.5 |  |  | $ | 1.7 |  |  | $ | 11.3 |
Salaried VEBA benefit payments 1 |  |  | 5.4 |  |  |  | 5.2 |  |  |  | 5.0 |  |  |  | 4.8 |  |  |  | 4.5 |  |  |  | 18.1 |
OPEB payments |  |  | 3.3 |  |  |  | 3.9 |  |  |  | 4.6 |  |  |  | 5.2 |  |  |  | 5.8 |  |  |  | 35.0 |
Total |  | $ | 9.5 |  |  | $ | 10.1 |  |  | $ | 10.8 |  |  | $ | 11.5 |  |  | $ | 12.0 |  |  | $ | 64.4 |
1. Such amounts are based on benefit amounts and certain key assumptions obtained from the Salaried VEBA trustees and will be paid out of the Salaried VEBA plan assets. We have an ongoing obligation to make variable cash contributions to the Salaried VEBA, up to a maximum of $2.9 million annually based on our cash flow.
Summary of Asset Class Allocation per Pension Plan Investment Policy and Weighted Average Asset Allocation | Plan Assets. The following table presents the asset class allocation per our pension plan investment policy and the weighted average asset allocation:
Asset class |  | Policy range |  | As of December 31, 2023
Equities |  | 54% - 60% |  | 59%
Fixed income |  | 35% - 40% |  | 35%
Other investments |  | 5% - 6% |  | 6%
Schedule of Fair Value of Plan Assets | The following table presents the fair value of plan assets at December 31, 2023 and 2022, classified under the appropriate level of the fair value hierarchy (in millions of dollars):
|  | December 31, 2023 |  |  | December 31, 2022 |  |
Plan Assets in the Fair Value Hierarchy: 4 |  | Level 1 |  |
Salaried VEBA – Equity investment funds in registered investment companies 1 |  | $ | 25.5 |  |  | $ | 27.4 |  |
Salaried VEBA – Fixed income investment funds in registered investment companies 2 |  |  | 16.5 |  |  |  | 15.0 |  |
Pension plans – Equity investment funds in registered investment companies 1 |  |  | 7.1 |  |  |  | 4.1 |  |
Pension plans – Fixed income investment funds in registered investment companies 2 |  |  | 4.1 |  |  |  | 2.6 |  |
Pension plans – Diversified investment funds in registered investment companies 3 |  |  | 9.3 |  |  |  | 8.2 |  |
Deferred compensation program – Diversified investment funds in registered investment companies 3 |  |  | 11.1 |  |  |  | 9.8 |  |
Total plan assets in the fair value hierarchy |  | $ | 73.6 |  |  | $ | 67.1 |  |
1. Equity investment funds in registered investment companies. This category represents investments in equity funds that invest in portfolios comprised primarily of equity and equity-related securities of U.S. and non-U.S. issuers across all market capitalizations. 2. Fixed income investment funds in registered investment companies. This category represents investments in various fixed income funds with multiple registered investment companies. Such funds invest primarily in bonds, debentures, notes, securities with equity and fixed-income characteristics, cash equivalents, securities backed by mortgages and other assets, loans, pooled or collective investment vehicles made up of fixed‑income securities and other fixed-income obligations of banks, corporations, and governmental authorities. 3. Diversified investment funds in registered investment companies. The plan assets are invested in investment funds that hold a diversified portfolio of: (i) U.S. and international debt and equity securities; (ii) fixed income securities such as corporate bonds and government bonds; (iii) mortgage-related securities; and (iv) cash and cash equivalents. 4. All plan assets were measured using Level 1 inputs.
Schedule of Total Expense Related to Benefit Plans | The following table presents the total expense related to all benefit plans (in millions of dollars):
|  | Year Ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |
Defined contribution plans 1 |  | $ | 18.1 |  |  | $ | 17.1 |  |  | $ | 13.9 |
Deferred compensation plan 2 |  |  | 1.2 |  |  |  | (0.6 | ) |  |  | 0.7 |
Multiemployer pension plans 1,3 |  |  | 5.6 |  |  |  | 5.2 |  |  |  | 5.0 |
Net periodic postretirement benefit cost relating to defined benefit plans 2,3,4 |  |  | 13.4 |  |  |  | 13.1 |  |  |  | 9.4 |
Total |  | $ | 38.3 |  |  | $ | 34.8 |  |  | $ | 29.0 |
1. Substantially all of these charges related to employee benefits are in COGS with the remaining balance in SG&A and R&D. 2. Deferred compensation plan expense and the current service cost component of Net periodic postretirement benefit cost relating to Salaried VEBA are included within our Statements of Consolidated Income (Loss) in SG&A and R&D for all periods presented. All other components of Net periodic postretirement benefit cost relating to Salaried VEBA are included within Other income (expense), net, in our Statements of Consolidated Income (Loss). 3. See Note 6 for more information on our multiemployer defined benefit pension plans. 4. The current service cost component of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within our Statements of Consolidated Income (Loss) in COGS for all periods presented. All other components of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within Other income (expense), net, in our Statements of Consolidated Income (Loss).
Schedule of Net Benefit Costs | The following table presents the components of Net periodic postretirement benefit cost relating to our defined benefit plans (in millions of dollars):
|  | Pension Plans |  |  | OPEB |  |  | Salaried VEBA |
|  | Year Ended December 31, |  |  | Year Ended December 31, |  |  | Year Ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |  |  | 2023 |  |  | 2022 |  |  | 2021 |  |  | 2023 |  |  | 2022 |  |  | 2021 |
Service cost |  | $ | 3.8 |  |  | $ | 5.8 |  |  | $ | 4.1 |  |  | $ | 1.1 |  |  | $ | 1.6 |  |  | $ | 1.1 |  |  | $ | — |  |  | $ | 0.1 |  |  | $ | 0.1 |
Interest cost |  |  | 1.3 |  |  |  | 0.6 |  |  |  | 0.5 |  |  |  | 3.4 |  |  |  | 2.2 |  |  |  | 1.7 |  |  |  | 2.9 |  |  |  | 1.9 |  |  |  | 1.5 |
Expected return on plan assets |  |  | (1.1 | ) |  |  | (0.9 | ) |  |  | (0.4 | ) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | (2.2 | ) |  |  | (3.1 | ) |  |  | (3.1 | )
Amortization of prior service cost 1 |  |  | 0.4 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 4.9 |  |  |  | 4.9 |  |  |  | 3.5 |
Amortization of net actuarial loss (gain) |  |  | — |  |  |  | — |  |  |  | 0.1 |  |  |  | (1.1 | ) |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.3 |
Total net periodic postretirement benefit cost |  | $ | 4.4 |  |  | $ | 5.5 |  |  | $ | 4.3 |  |  | $ | 3.4 |  |  | $ | 3.8 |  |  | $ | 2.8 |  |  | $ | 5.6 |  |  | $ | 3.8 |  |  | $ | 2.3 |
1. We amortize prior service cost on a straight-line basis over the average remaining years of service of the active plan participants.

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