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Postretirement Health Care and Life Insurance Benefits (Tables) | 12 Months Ended
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Dec. 31, 2025
Retirement Benefits [Abstract] |
Components of net periodic postretirement benefit credit | Net periodic postretirement benefit credit included the following components:
| Year Ended December 31,
| 2025 |  | 2024 |  | 2023
| (Dollars in millions)
Service cost for benefits earned | $ | 0.3 |  |  | $ | 0.5 |  |  | $ | 0.5 |
Interest cost on accumulated postretirement benefit obligation | 7.8 |  |  | 9.1 |  |  | 10.2 |
Expected return on plan assets | (0.3) |  |  | (0.4) |  |  | (0.5) |
Amortization of prior service credit | (40.8) |  |  | (53.0) |  |  | (53.8) |
Net actuarial gain | (8.5) |  |  | (17.0) |  |  | (2.6) |
Net periodic postretirement benefit credit | $ | (41.5) |  |  | $ | (60.8) |  |  | $ | (46.2) |
Amounts recognized in accumulated other comprehensive income | The following includes pretax amounts recorded in “Accumulated other comprehensive income”:
| Year Ended December 31,
| 2025 |  | 2024 |  | 2023
| (Dollars in millions)
Prior service credit arising during year | $ | — |  |  | $ | (6.5) |  |  | $ | — |
Amortization: |  |  |  |  |
Prior service credit | 40.8 |  |  | 53.0 |  |  | 53.8 |
Total recorded in “Accumulated other comprehensive income” | $ | 40.8 |  |  | $ | 46.5 |  |  | $ | 53.8 |
Reconciled amount of plan's funded status | The following table sets forth the plans’ funded status reconciled with the amounts shown in the consolidated balance sheets:
| December 31,
| 2025 |  | 2024
| (Dollars in millions)
Change in benefit obligation: |  |  |
Accumulated postretirement benefit obligation at beginning of period | $ | 145.4 |  |  | $ | 178.0 |
Service cost | 0.3 |  |  | 0.5 |
Interest cost | 7.8 |  |  | 9.1 |
Plan amendments | — |  |  | (6.5) |
Benefits paid and administrative fees (net of Medicare Part D reimbursements) | (15.2) |  |  | (18.8) |
Actuarial gain | (8.1) |  |  | (16.9) |
Accumulated postretirement benefit obligation at end of period | 130.2 |  |  | 145.4 |
Change in plan assets: |  |  |
Fair value of plan assets at beginning of period | 11.3 |  |  | 14.3 |
Actual return on plan assets | 0.8 |  |  | 0.5 |
Employer contributions | 12.2 |  |  | 15.3 |
Benefits paid and administrative fees (net of Medicare Part D reimbursements) | (15.2) |  |  | (18.8) |
Fair value of plan assets at end of period | 9.1 |  |  | 11.3 |
Funded status at end of period | (121.1) |  |  | (134.1) |
Less: Current portion (included in “Accounts payable and accrued expenses”) | 11.9 |  |  | 13.7 |
Noncurrent obligation (included in “Accrued postretirement benefit costs”) | $ | 109.2 |  |  | $ | 120.4 |
Weighted-average assumptions used to determine the benefit obligations | The weighted-average assumptions used to determine the benefit obligations for the plans as of the end of each year were as follows:
| December 31,
| 2025 |  | 2024
Discount rate | 5.39 | % |  | 5.70 | %
Measurement date | December 31, 2025 |  | December 31, 2024
The weighted-average assumptions used to determine net periodic postretirement benefit credit for the plans during each period were as follows:
| Year Ended December 31,
| 2025 |  | 2024 |  | 2023
Discount rate | 5.70 | % |  | 5.44 | % |  | 5.70 | %
Expected long-term return on plan assets (pretax) | 5.95 | % |  | 5.75 | % |  | 5.75 | %
Measurement date | December 31, 2024 |  | December 31, 2023 |  | December 31, 2022
Assumed health care cost trend rate | The following presents information about the assumed health care cost trend rate:
| Year Ended December 31,
| 2025 |  | 2024
Pre-Medicare: |  |  |
Health care cost trend rate assumed for next year | 7.00 | % |  | 6.50 | %
Rate to which the cost trend is assumed to decline (the ultimate trend rate) | 4.75 | % |  | 4.75 | %
Year that the rate reaches the ultimate trend rate | 2035 |  | 2032
Post-Medicare: |  |  |
Health care cost trend rate assumed for next year (1) | 6.75 | % |  | 6.15 | %
Rate to which the cost trend is assumed to decline (the ultimate trend rate) | 4.75 | % |  | 4.75 | %
Year that the rate reaches the ultimate trend rate | 2035 |  | 2032
(1) An additional one-time increase of 3% was applied to claims in 2024 to reflect potential reductions in payments from Center for Medicare and Medicaid Services related to the passage of the Inflation Reduction Act in August 2022.

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- Definition Tabular disclosure of the assumed health care cost trend rates for the next year used to measure the expected cost of benefits covered by the plans, including the ultimate trend rate(s) and when that rate is expected to be achieved. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (k) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (l) -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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- 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://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (q) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: 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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