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Components of Net Periodic Benefit Cost | 6 Months Ended
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Jun. 30, 2020
Components of net periodic benefit cost [Abstract] |
Components of Net Periodic Benefit Cost | Components of Net Periodic Benefit Cost
| Pension Benefits |  |  |  |  |  |  |  |  |  |
| Three months ended June 30, |  |  |  | Six months ended June 30, |  |  |  |  |  |
| 2020 |  | 2019 |  | 2020 |  | 2019 |  |  |  |
Service cost | $ | 1.1 |  |  | $ | 0.5 |  |  | $ | 2.4 |  |  | $ | 1.5 |  |  |  |  |
Interest cost | 2.8 |  |  | 3.4 |  |  | 5.6 |  |  | 6.7 |  |  |  |  |
Expected return on plan assets | (5.2) |  |  | (4.3) |  |  | (10.3) |  |  | (9.1) |  |  |  |  |
Amortization of prior service costs | 0.0 |  |  | 0.5 |  |  | 0.0 |  |  | 0.5 |  |  |  |  |
Amortization of net loss | 1.8 |  |  | 2.2 |  |  | 3.3 |  |  | 3.3 |  |  |  |  |
Net periodic benefit cost | $ | 0.5 |  |  | $ | 2.3 |  |  | $ | 1.0 |  |  | $ | 2.9 |  |  |  |  |
| Other Postretirement Benefits ("OPEB") |  |  |  |  |  |  |  |  |  |
| Three months ended June 30, |  |  |  | Six months ended June 30, |  |  |  |  |  |
| 2020 |  | 2019 |  | 2020 |  | 2019 |  |  |  |
Service cost | $ | 0.1 |  |  | $ | 0.7 |  |  | $ | 0.2 |  |  | $ | 0.7 |  |  |  |  |
Interest cost | 0.7 |  |  | 1.2 |  |  | 1.5 |  |  | 2.3 |  |  |  |  |
Amortization of prior service cost | (0.8) |  |  | (1.8) |  |  | (1.6) |  |  | (3.1) |  |  |  |  |
Amortization of net loss | 0.1 |  |  | 0.4 |  |  | 1.1 |  |  | 1.1 |  |  |  |  |
Net periodic benefit cost | $ | 0.1 |  |  | $ | 0.5 |  |  | $ | 1.2 |  |  | $ | 1.0 |  |  |  |  |

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- Definition Components of net periodic benefit cost [Abstract] + References No definition available. + Details
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