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Pension and Postretirement Benefit Costs (Tables) | 9 Months Ended
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Sep. 30, 2024
Retirement Benefits [Abstract] |
Schedule of Net Benefit Costs | Net periodic pension cost included the following components:
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2024 |  | 2023 |  | 2024 |  | 2023
| (Dollars in millions)
Service cost for benefits earned | $ | 0.1 |  |  | $ | 0.1 |  |  | $ | 0.1 |  |  | $ | 0.1 |
Interest cost on projected benefit obligation | 1.7 |  |  | 3.6 |  |  | 4.9 |  |  | 18.4 |
Expected return on plan assets | (1.3) |  |  | (3.1) |  |  | (3.7) |  |  | (16.3) |
Net periodic pension cost | $ | 0.5 |  |  | $ | 0.6 |  |  | $ | 1.3 |  |  | $ | 2.2 |
Net periodic postretirement benefit credit included the following components:
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2024 |  | 2023 |  | 2024 |  | 2023
| (Dollars in millions)
Service cost for benefits earned | $ | 0.1 |  |  | $ | 0.1 |  |  | $ | 0.3 |  |  | $ | 0.4 |
Interest cost on accumulated postretirement benefit obligation | 2.3 |  |  | 2.6 |  |  | 6.9 |  |  | 7.6 |
Expected return on plan assets | (0.1) |  |  | (0.1) |  |  | (0.3) |  |  | (0.4) |
Amortization of prior service credit | (13.3) |  |  | (13.5) |  |  | (39.8) |  |  | (40.3) |
Net periodic postretirement benefit credit | $ | (11.0) |  |  | $ | (10.9) |  |  | $ | (32.9) |  |  | $ | (32.7) |

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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