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Pension and Other Postemployment Benefits | 9 Months Ended
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Sep. 30, 2020
Pension and Other Postemployment Benefits [Abstract] |
Pension and Other Postemployment Benefits | Pension and Other Postemployment Benefits Defined Benefit Pension Plans The components of net periodic benefit expense were (in millions):
| Nine Months Ended September 30, |  |
| 2020 |  | 2019
Service cost | $ | 5.6 |  |  | $ | 6.4 |
Interest cost | 5.0 |  |  | 4.9 |
Expected return on plan assets | (0.7) |  |  | (1.1) |
Amortization of prior service cost | 0.5 |  |  | 0.6 |
Amortization of actuarial losses | 4.0 |  |  | 0.9 |
| $ | 14.4 |  |  | $ | 11.7 |
We contributed $0.9 million and $1.0 million to our defined benefit pension plans in the nine months ended September 30, 2020 and 2019, respectively. Postemployment Arrangements The components of net periodic benefit expense were (in millions):
| Nine Months Ended September 30, |  |
| 2020 |  | 2019
Service cost | $ | 3.5 |  |  | $ | 3.3 |
Interest cost | 2.6 |  |  | 3.3 |
Amortization of prior service cost | 3.2 |  |  | 3.3 |
Amortization of actuarial losses | 1.6 |  |  | 0.7 |
| $ | 10.9 |  |  | $ | 10.6 |

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