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Pension and Other Postemployment Benefits | 9 Months Ended
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Sep. 30, 2024
Pension and Other Postemployment Benefits [Abstract] |
Pension and Other Postemployment Benefits | Pension and Other Postemployment Benefits Net periodic benefit expense:
| Defined Benefit Pension Plans |  | Postemployment Arrangements
| Nine Months Ended September 30, |  | Nine Months Ended September 30,
| 2024 |  | 2023 |  | 2024 |  | 2023
Service cost | $ | 2.1 |  |  | $ | 2.5 |  |  | $ | 2.3 |  |  | $ | 2.6 |
Interest cost | 4.9 |  |  | 7.8 |  |  | 4.4 |  |  | 4.3 |
Expected return on plan assets | (0.6) |  |  | (0.7) |  |  | — |  |  | — |
Amortization of prior service cost | 0.3 |  |  | 0.2 |  |  | 3.3 |  |  | 2.9 |
Amortization of actuarial losses | 0.6 |  |  | 0.6 |  |  | 0.2 |  |  | — |
Total net periodic benefit expense | $ | 7.3 |  |  | $ | 10.4 |  |  | $ | 10.2 |  |  | $ | 9.8 |
In the nine months ended September 30, 2024 and 2023, we contributed $1.2 million and $0.3 million to our defined benefit pension plans, respectively.

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