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Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total net periodic postretirement and postemployment benefit cost (credit) | $ 1.2 | $ 1.5 | $ 3.8 | $ 3.3
Pension Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.9 | 0.7 | 2.6 | 2.7
Interest cost | 0.4 | 0.4 | 1.2 | 1.2
Expected return on plan assets | (0.4) | (0.3) | (1.1) | (1.0)
Amortization of prior service cost | 0.3 | 0.2 | 0.7 | 0.5
Amortization of net actuarial gain | (0.1) |  | (0.1) |
Total net periodic postretirement and postemployment benefit cost (credit) | 1.1 | 1.0 | 3.3 | 3.4
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.2 | 0.3 | 0.7 | 0.8
Interest cost | 0.9 | 0.8 | 2.6 | 2.5
Amortization of net actuarial gain | (0.5) | (0.3) | (1.4) | (0.8)
Total net periodic postretirement and postemployment benefit cost (credit) | 0.6 | 0.8 | 1.9 | 2.5
Postretirement Health Coverage | Salaried VEBA |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Interest cost | 0.6 | 0.5 | 1.7 | 1.6
Expected return on plan assets | (0.6) | (0.6) | (1.7) | (1.7)
Amortization of prior service cost | 0.7 | 0.8 | 2.2 | 1.0
Amortization of net actuarial gain | (0.1) |  | (0.3) |
Total net periodic postretirement and postemployment benefit cost (credit) | $ 0.6 | $ 0.7 | $ 1.9 | $ 0.9

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