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Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
Components of net periodic benefit cost |  |
Net periodic pension (benefit) cost | $ 2.8 | $ 4.9
Defined benefit pension plans |  |
Components of net periodic benefit cost |  |
Service cost for benefits earned | 0.0 | 0.5
Interest cost on projected benefit obligation | 7.0 | 8.3
Expected return on plan assets | (7.4) | (7.8)
Net periodic pension (benefit) cost | $ (0.4) | 1.0
Other Defined Benefit Plan Information [Abstract] |  |
Funding threshold | 80.00% |
Postretirement benefit plans |  |
Components of net periodic postretirement benefits cost |  |
Service cost for benefits earned | $ 1.1 | 1.2
Interest cost on accumulated postretirement benefit obligation | 5.5 | 6.3
Expected return on plan assets | (0.4) | (0.1)
Amortization of prior service credit | (2.2) | (2.2)
Net periodic postretirement benefit cost | $ 4.0 | $ 5.2

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