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Pension and Postretirement Benefit Costs - Schedule of Net Periodic Benefit (Benefit) Cost (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Net periodic postretirement benefit credit | $ (7.4) | $ (10.2) | $ (14.8) | $ (20.3)
Postretirement benefit plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost for benefits earned | 0.1 | 0.1 | 0.2 | 0.2
Interest cost on accumulated postretirement benefit obligation | 1.9 | 2.3 | 3.9 | 4.6
Expected return on plan assets | (0.1) | (0.1) | (0.2) | (0.2)
Amortization of prior service credit | (10.2) | (13.3) | (20.4) | (26.5)
Net periodic postretirement benefit credit | $ (8.3) | $ (11.0) | $ (16.5) | $ (21.9)

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