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Retirement Plans and Other Postretirement Benefits | 6 Months Ended
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Jun. 30, 2026
Retirement Benefits [Abstract] |
Retirement Plans and Other Postretirement Benefits | Retirement Plans and Other Postretirement Benefits Pinnacle West sponsors a qualified defined benefit and account balance pension plan, a non-qualified supplemental excess benefit retirement plan, and other postretirement benefit plans for the employees of Pinnacle West and our subsidiaries. The other postretirement benefit plans include a group life and medical plan and a post-65 retiree health reimbursement arrangement (“HRA”). Pinnacle West uses a December 31 measurement date each year for its pension and other postretirement benefit plans. Our plan assets are measured at fair value as of the measurement date. The following table provides detail of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction or billed to electric plant participants) (dollars in thousands):
|  |  |  |  |  |  |  |  |  |  |  |  | Pension Plans |  | Other Benefits Plans
|  |  |  |  | Three Months Ended June 30, |  | Six Months Ended June 30, |  | Three Months Ended June 30, |  | Six Months Ended June 30,
|  |  |  |  |  |  |  |  |  |  |  |  | 2026 |  | 2025 |  | 2026 |  | 2025 |  | 2026 |  | 2025 |  | 2026 |  | 2025
Service cost-benefits earned during the period |  |  |  |  |  |  |  |  |  |  |  |  | $ | 11,684 |  |  | $ | 11,127 |  |  | $ | 23,783 |  |  | $ | 22,076 |  |  | $ | 2,140 |  |  | $ | 2,059 |  |  | $ | 4,377 |  |  | $ | 4,041 |
Non-service costs (credits): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest cost on benefit obligation |  |  |  |  |  |  |  |  |  |  |  |  | 37,292 |  |  | 38,584 |  |  | 74,904 |  |  | 77,560 |  |  | 4,931 |  |  | 5,070 |  |  | 9,910 |  |  | 10,172 |
Expected return on plan assets |  |  |  |  |  |  |  |  |  |  |  |  | (44,365) |  |  | (44,849) |  |  | (88,461) |  |  | (89,396) |  |  | (12,719) |  |  | (12,142) |  |  | (25,438) |  |  | (24,284) |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Prior service cost (credit) |  |  |  |  |  |  |  |  |  |  |  |  | 151 |  |  | — |  |  | 302 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (1,265) |
Net actuarial loss (gain) |  |  |  |  |  |  |  |  |  |  |  |  | 10,443 |  |  | 11,248 |  |  | 21,596 |  |  | 23,366 |  |  | (2,746) |  |  | (2,965) |  |  | (5,446) |  |  | (5,864) |
Net periodic benefit costs (credits) |  |  |  |  |  |  |  |  |  |  |  |  | $ | 15,205 |  |  | $ | 16,110 |  |  | $ | 32,124 |  |  | $ | 33,606 |  |  | $ | (8,394) |  |  | $ | (7,978) |  |  | $ | (16,597) |  |  | $ | (17,200) |
Portion of costs (credits) charged to expense |  |  |  |  |  |  |  |  |  |  |  |  | $ | 8,262 |  |  | $ | 9,365 |  |  | $ | 17,780 |  |  | $ | 19,826 |  |  | $ | (6,644) |  |  | $ | (6,399) |  |  | $ | (13,153) |  |  | $ | (13,272) |
Contributions Future year contribution amounts are dependent on plan asset performance and plan actuarial assumptions. The expected minimum required cash contributions for the pension plan are zero for the next three years. However, while we do not expect to make a voluntary contribution in 2026, we are evaluating whether to make voluntary contributions in 2027 and 2028. The amount of voluntary contributions will be determined as we continue to evaluate and assess our ongoing contribution strategy. Regarding contributions to our other postretirement benefit plan, we have not made a contribution year-to-date in 2026 and do not expect to make any contributions in 2026, 2027 or 2028. The Company was reimbursed $23 million in April 2026 for prior year’s retiree medical claims from the other postretirement benefit plan trust assets.

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