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Retirement Plans | 9 Months Ended
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Sep. 30, 2025
Retirement Plans [Abstract] |
Retirement Plans | (17) Retirement Plans: Frontier recognizes actuarial gains (losses) for our pension and postretirement plans in the period they occur. The components of net periodic benefit cost other than the service cost component for our plans as well as any actuarial gains or losses are included in “Investment and other income (loss)” on the consolidated statements of operations. The following tables provide the components of total pension benefit cost:
|  |  |  | Pension Benefits |
|  |  | For the three months ended September 30, |  | For the nine months ended ‎September 30, |
| ($ in millions) |  | 2025 |  | 2024 |  | 2025 |  | 2024 |
| Components of total pension benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |
| Service cost |  | $ | 11 |  | $ | 11 |  | $ | 33 |  | $ | 34 |
| Interest cost on projected benefit obligation |  |  | 31 |  |  | 31 |  |  | 95 |  |  | 94 |
| Expected return on plan assets |  |  | (38) |  |  | (40) |  |  | (114) |  |  | (124) |
| Pension remeasurement gain |  |  | - |  |  | (23) |  |  | (44) |  |  | (25) |
| Pension building sale - loss |  |  | 19 |  |  | - |  |  | 19 |  |  | - |
| Net periodic pension (benefit) costs |  |  | 23 |  |  | (21) |  |  | (11) |  |  | (21) |
| Pension special termination benefit enhancements |  |  | - |  |  | 1 |  |  | - |  |  | 11 |
| Total pension (benefit) cost |  | $ | 23 |  | $ | (20) |  | $ | (11) |  | $ | (10) |
The components of net periodic benefit cost other than the service cost component are included in “Investment and other income” on the consolidated statements of operations. The value of our pension plan assets increased $188 million from $2,328 million at December 31, 2024 to $2,516 million at September 30, 2025. This increase primarily resulted from changes in the market value of investments of $193 million, net of plan expenses, and contributions of $112 million, offset by benefit payments to participants of $117 million. As a result of special termination benefit enhancements related to a voluntary separation plan, Frontier remeasured its pension plan obligations, resulting in a remeasurement gain of $0 million and $44 million for the three and nine months ended September 30, 2025, respectively. The pension plan contains provisions that provide certain employees with the option of receiving a lump sum payment upon retirement. Frontier’s accounting policy is to record these payments as a settlement only if, in the aggregate, they exceed the sum of the annual service and interest costs for the Pension Plan’s net periodic pension benefit cost. In the first nine months of 2025, the Company recognized a minimal charge to reflect the cost of pension special termination benefit enhancements related to a voluntary separation plan, compared to a charge of $11 million as of September 30, 2024. ‎ The following table provides the components of total postretirement benefit cost:
|  |  |  | Postretirement |
|  |  | For the three months ended September 30, |  | For the nine months ended September 30, |
| ($ in millions) |  | 2025 |  | 2024 |  | 2025 |  | 2024 |
| Components of net periodic postretirement benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |
| Service cost |  | $ | 3 |  | $ | 2 |  | $ | 5 |  | $ | 5 |
| Interest cost on projected benefit obligation |  |  | 8 |  |  | 7 |  |  | 22 |  |  | 22 |
| Amortization of prior service credit gain recognized |  |  | (7) |  |  | (6) |  |  | (19) |  |  | (19) |
| OPEB remeasurement (gain) loss |  |  | - |  |  | 21 |  |  | 8 |  |  | (6) |
| Total periodic postretirement (benefit) cost |  | $ | 4 |  | $ | 24 |  | $ | 16 |  | $ | 2 |
As a result of special termination benefit enhancements related to a voluntary separation plan, Frontier remeasured its postretirement benefit plan, resulting in a remeasurement loss of $0 million and $8 million for the three and nine months ended September 30, 2025. As a result of special termination benefit enhancements related to a voluntary separation plan, Frontier remeasured its postretirement benefit plan, resulting in a remeasurement loss of $21 million and a remeasurement gain of $6 million for the three and nine months ended September 30, 2024, respectively. We capitalized $13 million of pension and OPEB expense for both nine months ended September 30, 2025 and 2024, respectively, into the cost of our capital expenditures, as the costs relate to our engineering and plant construction activities.

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