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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, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Net periodic postretirement benefit cost: |  |  |  |
Total net periodic postretirement benefit cost | $ 1.2 | $ 1.2 | $ 1.8 | $ 2.4
Postretirement Health Coverage | Salaried VEBA |  |  |  |
Net periodic postretirement benefit cost: |  |  |  |
Interest cost | 0.4 | 0.7 | 0.8 | 1.3
Expected return on plan assets | (0.8) | (0.7) | (1.6) | (1.4)
Amortization of prior service cost | 0.8 | 1.1 | 1.7 | 2.3
Amortization of net actuarial loss | 0.1 | 0.1 | 0.2 | 0.2
Total net periodic postretirement benefit cost | 0.5 | $ 1.2 | 1.1 | $ 2.4
Pension Plan | Warrick Rolling Mill |  |  |  |
Net periodic postretirement benefit cost: |  |  |  |
Service cost | 1.2 |  | 1.2 |
Interest cost | 0.1 |  | 0.1 |
Total net periodic postretirement benefit cost | 1.3 |  | 1.3 |
Other Postretirement Benefits Plan | Warrick Rolling Mill |  |  |  |
Net periodic postretirement benefit cost: |  |  |  |
Service cost | 0.4 |  | 0.4 |
Interest cost | 0.6 |  | 0.6 |
Total net periodic postretirement benefit cost | $ 1.0 |  | $ 1.0 |

X
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