v3.25.1
Retirement Plans and Other Postretirement Benefits
 3 Months Ended
Mar. 31, 2025
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.  The market-related value of our plan assets is their fair value at 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 PlansOther Benefits Plans
Three Months Ended March 31,Three Months Ended March 31,
 2025202420252024
Service cost-benefits earned during the period$10,949 $10,631 $1,982 $2,459 
Non-service costs (credits):
Interest cost on benefit obligation38,976 37,236 5,102 5,613 
Expected return on plan assets(44,547)(46,983)(12,142)(11,709)
Amortization of:
Prior service credit (a)— — (1,265)(9,447)
Net actuarial loss (gain)
12,118 10,944 (2,899)(2,080)
Net periodic benefit costs (credits)
$17,496 $11,828 $(9,222)$(15,164)
Portion of costs (credits) charged to expense
$10,461 $6,337 $(6,873)$(11,306)
(a)    Prior-service costs or credits reflect the impact of modifications to the pension or postretirement plan benefits. The impact of these modifications is amortized over a period which reflects the demographics of the impacted population. In 2014, Pinnacle West made changes to the postretirement benefits offered to Medicare eligible retirees which resulted in prior-service credits. We have been amortizing these prior-serviced credits since 2015 and they became fully amortized as of January 31, 2025.
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 and we do not expect to make any voluntary contributions in 2025, 2026 or 2027. With regard to contributions to our other postretirement benefit plan, we have not made a contribution year-to-date in 2025 and do not expect to make any contributions in 2025, 2026 or 2027.