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Retirement Plans and Other Postretirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Schedule of Net Periodic Benefit Costs and the Portion of these Costs Charged to Expense (Including Administrative Costs and Excluding Amounts Capitalized as Overhead Construction, Billed to Electric Plant Participants or Charged or Amortized to the Regulatory Asset)
The following table provides details 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
 202420232022202420232022
Service cost-benefits earned during the period$43,641 $39,461 $55,473 $9,955 $8,567 $16,470 
Non-service costs (credits):
Interest cost on benefit obligation148,643 153,561 107,492 22,169 22,509 17,491 
Expected return on plan assets(188,651)(182,938)(185,775)(46,834)(43,486)(46,042)
Amortization of:
Prior service credit (a)— — — (37,789)(37,789)(37,789)
Net actuarial loss (gain)
41,915 38,420 17,515 (8,676)(9,614)(12,835)
Net periodic benefit costs (credits)
$45,548 $48,504 $(5,295)$(61,175)$(59,813)$(62,705)
Portion of costs (credits) charged to expense
$23,652 $27,029 $(16,431)$(45,557)$(43,408)$(45,042)
(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 with the last full-year amortization occurring in 2024.
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
 2024202320242023
Change in Benefit Obligation    
Benefit obligation at January 1$2,908,063 $2,809,529 $430,434 $409,461 
Service cost43,641 39,461 9,955 8,567 
Interest cost148,643 153,561 22,169 22,509 
Benefit payments(216,238)(210,737)(30,516)(30,784)
Actuarial (gain) loss(91,800)116,249 (71,952)20,681 
Benefit obligation at December 312,792,309 2,908,063 360,090 430,434 
Change in Plan Assets    
Fair value of plan assets at January 12,835,549 2,829,485 696,494 652,287 
Actual return on plan assets4,518 199,098 32,816 67,317 
Benefit payments(200,205)(193,034)(27,118)(23,110)
Fair value of plan assets at December 312,639,862 2,835,549 702,192 696,494 
Funded (Underfunded) Status at December 31$(152,447)$(72,514)$342,102 $266,060 
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,
 20242023
Accumulated benefit obligation$113,541 $123,701 
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,
 20242023
Projected benefit obligation$2,792,309 $129,891 
Fair value of plan assets2,639,862 — 
Schedule of Amounts Recognized on the Consolidated Balance Sheets
The following table shows the amounts recognized on the Consolidated Balance Sheets (dollars in thousands):
 Pension PlansOther Benefits Plans
 2024202320242023
Noncurrent asset$— $57,378 $342,102 $266,060 
Current liability(13,130)(17,190)— — 
Noncurrent liability(139,317)(112,702)— — 
Net amount recognized (funded status)$(152,447)$(72,514)$342,102 $266,060 
Schedule of Accumulated Other Comprehensive Loss
The following table shows the details related to accumulated other comprehensive loss (gain) as of December 31, 2024, and 2023 (dollars in thousands): 
 Pension PlansOther Benefits Plans
 2024202320242023
Net actuarial loss (gain)$793,421 $743,003 $(237,889)$(188,630)
Prior service credit— — (1,265)(39,054)
APS’s portion recorded as a regulatory (asset) liability(750,976)(696,476)238,113 226,726 
Income tax expense (benefit)(10,354)(11,506)611 691 
Accumulated other comprehensive loss (gain)$32,091 $35,021 $(430)$(267)
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,
 20242023202420232022
Discount rate – pension plans5.68 %5.21 %5.21 %5.56 %2.92 %
Discount rate – other benefits plans5.71 %5.23 %5.23 %5.58 %2.98 %
Rate of compensation increase4.50 %4.52 %4.52 %4.57 %4.00 %
Expected long-term return on plan assets - pension plansN/AN/A6.90 %6.70 %5.00 %
Expected long-term return on plan assets - other benefit plansN/AN/A6.85 %6.80 %5.35 %
Initial healthcare cost trend rate (pre-65 participants)6.50 %6.25 %6.25 %6.50 %6.00 %
Ultimate healthcare cost trend rate (pre-65 participants)4.50 %4.75 %4.75 %4.75 %4.75 %
Number of years to ultimate trend rate (pre-65 participants)65453
Initial healthcare cost trend rate (post-65 participants)1.00 %2.00 %2.00 %2.00 %2.00 %
Ultimate healthcare cost trend rate (post-65 participants)— %2.00 %2.00 %2.00 %2.00 %
Interest crediting rate – cash balance pension plans4.66 %4.54 %4.54 %4.50 %4.50 %
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, 2024, are as follows:
 Target AllocationActual Allocation
Long-term fixed income assets80 %79 %
Return-seeking assets20 %21 %
Total100 %100 %

The permissible range is within +/-5% of the target allocation shown in the above table, and also considers the plan’s funded status.

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, 2024:
Actual Allocation
Long-term fixed income assets61 %
Return-seeking assets39 %
Total100 %
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 $702,192 
(a)These investments primarily represent assets valued using NAV as a practical expedient and have not been classified in the fair value hierarchy.
(b)This category consists primarily of debt securities issued by municipalities and asset backed securities.
(c)This category primarily consists of U.S. common stock equities.
(d)These funds invest in international common stock equities.
(e)Primarily relates to short-term investment funds and includes plan receivables and payables.
The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2023, by asset category, are as follows (dollars in thousands):
 Level 1Level 2Other (a)Total
Pension Plan:   
Fixed income securities:   
Corporate$— $1,415,346 $— $1,415,346 
U.S. Treasury622,273 — — 622,273 
Other (b)— 135,184 — 135,184 
Common stock equities (c)150,657 — — 150,657 
Mutual funds (d)112,791 — — 112,791 
Common and collective trusts:
   Equities— — 192,945 192,945 
   Real estate— — 140,613 140,613 
Other (e)— — 65,740 65,740 
Total $885,721 $1,550,530 $399,298 $2,835,549 
Other Benefits:    
Fixed income securities:   
Corporate$— $189,902 $— $189,902 
U.S. Treasury207,665 — — 207,665 
Other (b)— 8,372 — 8,372 
Common stock equities (c)139,952 — — 139,952 
Mutual funds (d)22,256 — — 22,256 
Common and collective trusts:
   Equities— — 81,724 81,724 
   Real estate— — 20,001 20,001 
Other (e)21,146 — 5,476 26,622 
Total $391,019 $198,274 $107,201 $696,494 
(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)
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
2025$241,762 $28,753 
2026223,562 28,747 
2027230,335 28,276 
2028233,617 27,880 
2029232,591 27,645 
Years 2030-20341,147,273 137,301