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Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total net periodic postretirement benefit cost | $ 1.9 | $ 1.5 | $ 3.9 | $ 2.9
Pension Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.8 | 1.4 | 1.8 | 2.8
Interest cost | 0.3 | 0.1 | 0.6 | 0.3
Expected return on plan assets | (0.2) | (0.2) | (0.5) | (0.4)
Amortization of prior service cost | 0.1 |  | 0.1 |
Total net periodic postretirement benefit cost | 1.0 | 1.3 | 2.0 | 2.7
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Service cost | 0.2 | 0.4 | 0.5 | 0.8
Interest cost | 0.9 | 0.6 | 1.7 | 1.1
Amortization of net actuarial loss (gain) | (0.3) |  | (0.6) |
Total net periodic postretirement benefit cost | 0.8 | 1.0 | 1.6 | 1.9
Postretirement Health Coverage | Salaried VEBA |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Interest cost | 0.7 | 0.4 | 1.4 | 0.9
Expected return on plan assets | (0.5) | (0.7) | (1.1) | (1.5)
Amortization of prior service cost | 1.3 | 1.3 | 2.5 | 2.5
Total net periodic postretirement benefit cost | $ 1.5 | $ 1.0 | $ 2.8 | $ 1.9

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