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Retirement Plans and Other Postretirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2025
Retirement Benefits [Abstract]  
Schedule of Net Periodic Benefit Costs and the Portion of these Costs Charged to Expense
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
 202520242023202520242023
Service cost-benefits earned during the period$44,153 $43,641 $39,461 $8,081 $9,955 $8,567 
Non-service costs (credits):
Interest cost on benefit obligation155,121 148,643 153,561 20,345 22,169 22,509 
Expected return on plan assets(178,793)(188,651)(182,938)(48,569)(46,834)(43,486)
Amortization of:
Prior service credit (a)— — — (1,265)(37,789)(37,789)
Net actuarial loss (gain)
46,731 41,915 38,420 (11,727)(8,676)(9,614)
Net periodic benefit costs (credits)
$67,212 $45,548 $48,504 $(33,135)$(61,175)$(59,813)
Portion of costs (credits) charged to expense
$38,977 $23,652 $27,029 $(25,736)$(45,557)$(43,408)
(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.
Schedule of Changes in the Benefit Obligations and Funded Status
The following table shows the plans’ changes in the benefit obligations and funded status (dollars in thousands):
 Pension PlansOther Benefits Plans
 2025202420252024
Change in Benefit Obligation    
Benefit obligation at January 1$2,792,309 $2,908,063 $360,090 $430,434 
Service cost44,153 43,641 8,081 9,955 
Interest cost155,121 148,643 20,345 22,169 
Benefit payments(226,888)(216,238)(28,293)(30,516)
Actuarial (gain) loss79,363 (91,800)7,759 (71,952)
Other plan changes6,752 — — — 
Benefit obligation at December 312,850,810 2,792,309 367,982 360,090 
Change in Plan Assets    
Fair value of plan assets at January 12,639,862 2,835,549 702,192 696,494 
Actual return on plan assets244,343 4,518 65,124 32,816 
Benefit payments(213,684)(200,205)— (27,118)
Fair value of plan assets at December 312,670,521 2,639,862 767,316 702,192 
Funded (Underfunded) Status at December 31$(180,289)$(152,447)$399,334 $342,102 
Schedule of Projected Benefit Obligation and the Accumulated Benefit Obligation for Pension Plans with an Accumulated Obligation in Excess of Plan Assets
The following table shows information for pension plans with an accumulated obligation in excess of plan assets (dollars in thousands):
As of December 31,
 20252024
Accumulated benefit obligation$113,245 $113,541 
Fair value of plan assets— — 
The following table shows information for pension plans with a projected benefit obligation in excess of plan assets (dollars in thousands):
As of December 31,
 20252024
Projected benefit obligation$2,850,810 $2,792,309 
Fair value of plan assets2,670,521 2,639,862 
Schedule of Amounts Recognized on the Consolidated Balance Sheets
The following table shows the amounts recognized on the Consolidated Balance Sheets (dollars in thousands):
 Pension PlansOther Benefits Plans
 2025202420252024
Noncurrent asset$— $— $399,334 $342,102 
Current liability(12,653)(13,130)— — 
Noncurrent liability(167,636)(139,317)— — 
Net amount recognized (funded status)$(180,289)$(152,447)$399,334 $342,102 
Schedule of Accumulated Other Comprehensive Loss
The following table shows the details related to accumulated other comprehensive loss (gain) as of December 31, 2025, and 2024 (dollars in thousands): 
 Pension PlansOther Benefits Plans
 2025202420252024
Net actuarial loss (gain)$760,502 $793,421 $(234,958)$(237,889)
Prior service cost (credit)6,752 — — (1,265)
APS’s portion recorded as a regulatory (asset) liability(723,042)(750,976)233,952 238,113 
Income tax expense (benefit)(10,929)(10,354)703 611 
Accumulated other comprehensive loss (gain)$33,283 $32,091 $(303)$(430)
Schedule of Weighted-Average Assumptions Used for Both the Pension and Other Benefits to Determine Benefit Obligations and Net Periodic Benefit Costs
The following table shows the weighted-average assumptions used for both the pension and other benefits to determine benefit obligations and net periodic benefit costs:
 Benefit Obligations
As of December 31,		Benefit Costs
Year Ended December 31,
 20252024202520242023
Discount rate – pension plans5.36 %5.68 %5.68 %5.21 %5.56 %
Discount rate – other benefits plans5.43 %5.71 %5.71 %5.23 %5.58 %
Rate of compensation increase4.50 %4.50 %4.50 %4.52 %4.57 %
Expected long-term return on plan assets - pension plansN/AN/A7.05 %6.90 %6.70 %
Expected long-term return on plan assets - other benefit plansN/AN/A7.05 %6.85 %6.80 %
Initial healthcare cost trend rate (pre-65 participants)6.50 %6.50 %6.50 %6.25 %6.50 %
Ultimate healthcare cost trend rate (pre-65 participants)4.50 %4.50 %4.50 %4.75 %4.75 %
Number of years to ultimate trend rate (pre-65 participants)76645
Initial healthcare cost trend rate (post-65 participants) (a)N/A1.00 %1.00 %2.00 %2.00 %
Ultimate healthcare cost trend rate (post-65 participants) (a)N/A— %N/A2.00 %2.00 %
Interest crediting rate – cash balance pension plans4.51 %4.66 %4.66 %4.54 %4.50 %
(a) The Company has decided and has communicated to retirees that the increase in 2026 will be 1% with no further indexation in future years. Therefore, no assumption is being made for the Post-65 HRA subsidy trend rate.
Schedule of Fair Value of Pension Plan and Other Postretirement Benefit Plan Assets, by Asset Category
Based on the IPS, the target and actual allocation for the pension plan at December 31, 2025, are as follows:
 Target AllocationActual Allocation
Long-term fixed income assets80 %78 %
Return-seeking assets20 %22 %
Total100 %100 %
The following table presents the additional target allocations, as a percent of total pension plan assets, for the return-seeking assets:
Target Allocation
Equities in US and other developed markets12 %
Equities in emerging markets4 %
Alternative investments4 %
Total20 %
The following table presents the actual allocations of the investment for the other postretirement benefit plan at December 31, 2025:
Actual Allocation
Long-term fixed income assets59 %
Return-seeking assets41 %
Total100 %
The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2025, by asset category, are as follows (dollars in thousands):
 
 Level 1Level 2Other (a)Total
Pension Plan:   
Cash and cash equivalents$1,756 $— $— $1,756 
Fixed income securities:   
Corporate— 1,300,163 — 1,300,163 
U.S. Treasury607,621 — — 607,621 
Other (b)— 120,483 — 120,483 
Common stock equities (c)73,548 — — 73,548 
Mutual funds (d)115,478 — — 115,478 
Common and collective trusts:
Equities— — 266,624 266,624 
Real estate— — 114,782 114,782 
Other (e)— — 70,066 70,066 
Total$798,403 $1,420,646 $451,472 $2,670,521 
Other Benefits:    
Cash and cash equivalents$475 $— $— $475 
Fixed income securities:   
Corporate— 200,469 — 200,469 
U.S. Treasury165,294 — — 165,294 
Other (b)— 10,997 — 10,997 
Common stock equities (c)98,296 — — 98,296 
Mutual funds (d)27,986 — — 27,986 
Common and collective trusts:   
Equities— — 167,103 167,103 
Real estate— — 20,228 20,228 
Other (e)69,954 — 6,514 76,468 
Total$362,005 $211,466 $193,845 $767,316 
(a)These investments primarily represent assets valued using NAV as a practical expedient and have not been classified in the fair value hierarchy.
(b)This category consists primarily of debt securities issued by municipalities and asset backed securities.
(c)This category primarily consists of U.S. common stock equities.
(d)These funds invest in international common stock equities.
(e)Primarily relates to short-term investment funds and includes plan receivables and payables.
The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2024, by asset category, are as follows (dollars in thousands):
 Level 1Level 2Other (a)Total
Pension Plan:   
Cash and cash equivalents$9,055 $— $— $9,055 
Fixed income securities:   
Corporate— 1,325,833 — 1,325,833 
U.S. Treasury561,317 — — 561,317 
Other (b)— 133,254 — 133,254 
Common stock equities (c)74,939 — — 74,939 
Mutual funds (d)102,722 — — 102,722 
Common and collective trusts:
   Equities— — 244,734 244,734 
   Real estate— — 127,397 127,397 
Other (e)— — 60,611 60,611 
Total $748,033 $1,459,087 $432,742 $2,639,862 
Other Benefits:    
Cash and cash equivalents$840 $— $— $840 
Fixed income securities:   
Corporate— 186,435 — 186,435 
U.S. Treasury204,274 — — 204,274 
Other (b)— 12,585 — 12,585 
Common stock equities (c)89,685 — — 89,685 
Mutual funds (d)23,415 — — 23,415 
Common and collective trusts:
   Equities— — 140,178 140,178 
   Real estate— — 19,474 19,474 
Other (e)19,145 — 6,161 25,306 
Total $337,359 $199,020 $165,813 $702,192 
(a)These investments primarily represent assets valued using NAV as a practical expedient and have not been classified in the fair value hierarchy.
(b)This category consists primarily of debt securities issued by municipalities and asset backed securities.
(c)This category primarily consists of U.S. common stock equities.
(d)These funds invest in U.S. and international common stock equities.
(e)Primarily relates to short-term investment funds and includes plan receivables and payables.
Schedule of Estimated Future Benefit Payments, which Reflect Estimated Future Employee Service, for the Next Five Years and the Succeeding Five Years Thereafter
Benefit payments, which reflect estimated future employee service, for the next five years and the succeeding five years thereafter, are estimated to be as follows (dollars in thousands):
YearPension PlansOther Benefits Plans
2026$244,947 $28,075 
2027232,977 27,751 
2028235,256 27,443 
2029235,980 27,357 
2030235,953 27,206 
Years 2031-20351,149,488 137,689