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Retirement Plans and Other Postretirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2020
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
 202020192018202020192018
Service cost-benefits earned during the period
$56,233 $49,902 $56,669 $22,236 $18,369 $21,100 
Interest cost on benefit obligation118,567 136,843 124,689 25,857 29,894 28,147 
Expected return on plan assets(187,443)(171,884)(182,853)(40,077)(38,412)(42,082)
Amortization of:      
Prior service credit— — — (37,575)(37,821)(37,842)
Net actuarial loss34,612 42,584 32,082 — — — 
Net periodic benefit cost/(benefit)$21,969 $57,445 $30,587 $(29,559)$(27,970)$(30,677)
Portion of cost/(benefit) charged to expense$3,386 $30,312 $10,120 $(20,966)$(19,859)$(21,426)
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
 2020201920202019
Change in Benefit Obligation    
Benefit obligation at January 1$3,613,114 $3,190,626 $746,924 $676,771 
Service cost56,233 49,902 22,236 18,369 
Interest cost118,567 136,843 25,857 29,894 
Benefit payments(191,704)(177,882)(31,511)(32,486)
Actuarial (gain) loss306,657 413,625 (139,472)54,376 
Benefit obligation at December 313,902,867 3,613,114 624,034 746,924 
Change in Plan Assets    
Fair value of plan assets at January 13,318,351 2,733,476 837,494 723,677 
Actual return on plan assets642,373 602,030 150,076 144,095 
Employer contributions100,000 150,000 — — 
Benefit payments(174,180)(167,155)(26,405)(30,278)
Fair value of plan assets at December 313,886,544 3,318,351 961,165 837,494 
Funded Status at December 31$(16,323)$(294,763)$337,131 $90,570 
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,
 20202019
Accumulated benefit obligation171,672 169,091 
Fair value of plan assets— — 
 
The Pinnacle West Capital Corporation Retirement Plan is more than 100% funded on an accumulated benefit obligation basis at December 31, 2020 and December 31, 2019, therefore the only pension plan with an accumulated benefit obligation in excess of plan assets in 2020 and 2019 is a non-qualified supplemental excess benefit retirement plan.

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,
 20202019
Projected benefit obligation182,184 3,613,114 
Fair value of plan assets— 3,318,351 
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
 2020201920202019
Noncurrent asset$165,861 $— $337,131 $90,570 
Current liability(15,700)(14,578)— — 
Noncurrent liability(166,484)(280,185)— — 
Net amount recognized$(16,323)$(294,763)$337,131 $90,570 
Schedule of accumulated other comprehensive loss
The following table shows the details related to accumulated other comprehensive loss as of December 31, 2020 and 2019 (dollars in thousands): 
 Pension PlansOther Benefits Plans
 2020201920202019
Net actuarial loss (gain)$552,301 $735,186 $(237,233)$12,238 
Prior service credit— — (152,337)(189,912)
APS’s portion recorded as a regulatory (asset) liability(469,953)(660,223)387,293 177,209 
Income tax expense (benefit)(20,364)(18,546)1,018 570 
Accumulated other comprehensive loss (gain)$61,984 $56,417 $(1,259)$105 
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
For the Years Ended December 31,
 20202019202020192018
Discount rate – pension plans2.53 %3.30 %3.30 %4.34 %3.65 %
Discount rate – other benefits plans2.63 %3.42 %3.42 %4.39 %3.71 %
Rate of compensation increase4.00 %4.00 %4.00 %4.00 %4.00 %
Expected long-term return on plan assets - pension plansN/AN/A5.75 %6.25 %6.05 %
Expected long-term return on plan assets - other benefit plansN/AN/A4.85 %5.40 %5.40 %
Initial healthcare cost trend rate (pre-65 participants)6.50 %7.00 %7.00 %7.00 %7.00 %
Ultimate healthcare cost trend rate (pre-65 participants)4.75 %4.75 %4.75 %4.75 %4.75 %
Number of years to ultimate trend rate (pre-65 participants)56578
Initial and ultimate healthcare cost trend rate (post-65 participants) (a)2.00 %4.75 %4.75 %4.75 %4.75 %
Interest crediting rate – cash balance pension plans4.50 %4.50 %4.50 %4.50 %4.50 %
 
(a)See discussion above relating to this assumptions impact on benefit obligations and the January 2021 asset transfer to the Active Union Employee Medical Account.
Schedule of fair value of pension plan and other postretirement benefit plan assets, by asset category
Based on the IPS, and given the pension plan’s funded status at year-end 2020, the target and actual allocation for the pension plan at December 31, 2020 are as follows:
Pension Plans
 Target AllocationActual Allocation
Long-term fixed income assets72 %68 %
Return-generating assets28 %32 %
Total100 %100 %

The permissible range is within +/-3% of the target allocation shown in the above table, and also considers the plan’s funded status. At December 31, 2020, the return-seeking assets were slightly outside the target allocation permissible range and were rebalanced to within the target range during January 2021.

The following table presents the additional target allocations, as a percent of total pension plan assets, for the return-generating assets:
Asset ClassTarget Allocation
Equities in US and other developed markets17 %
Equities in emerging markets6 %
Alternative investments5 %
Total28 %
The following table presents the actual allocations of the investment for the other postretirement benefit plan at December 31, 2020:
Other Benefits Plans
Actual Allocation
Long-term fixed income assets55 %
Return-generating assets45 %
Total100 %
The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2020, by asset category, are as follows (dollars in thousands):
 
 Level 1Level 2Other (a)Total
Pension Plan:   
Cash and cash equivalents$9,911 $— $— $9,911 
Fixed income securities:   
Corporate— 1,684,782 — 1,684,782 
U.S. Treasury794,571 — — 794,571 
Other (b)— 112,224 — 112,224 
Common stock equities (c)331,058 — — 331,058 
Mutual funds (d)262,765 — — 262,765 
Common and collective trusts:
   Equities— — 407,522 407,522 
   Real estate— — 191,595 191,595 
Partnerships— — 22,420 22,420 
Short-term investments and other (e)— — 69,696 69,696 
Total $1,398,305 $1,797,006 $691,233 $3,886,544 
Other Benefits:    
Cash and cash equivalents$1,909 $— $— $1,909 
Fixed income securities:   
Corporate— 221,488 — 221,488 
U.S. Treasury258,102 — — 258,102 
Other (b)— 8,316 — 8,316 
Common stock equities (c)175,605 — — 175,605 
Mutual funds (d)34,310 — — 34,310 
Common and collective trusts:   
   Equities— — 94,674 94,674 
   Real estate— — 19,778 19,778 
Short-term investments and other (e)142,995 — 3,988 146,983 
Total $612,921 $229,804 $118,440 $961,165 
(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.
(c)This category primarily consists of U.S. common stock equities.
(d)These funds invest in international common stock equities.
(e)This category includes plan receivables and payables.
The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2019, by asset category, are as follows (dollars in thousands):
 Level 1Level 2Other (a)Total
Pension Plan:   
Cash and cash equivalents$9,370 $— $— $9,370 
Fixed income securities:   
Corporate— 1,541,729 — 1,541,729 
U.S. Treasury406,112 — — 406,112 
Other (b)— 92,240 — 92,240 
Common stock equities (c)250,829 — — 250,829 
Mutual funds (d)185,928 — — 185,928 
Common and collective trusts:
   Equities— — 392,403 392,403 
   Real estate— — 171,645 171,645 
   Fixed Income— — 98,065 98,065 
Partnerships— — 103,796 103,796 
Short-term investments and other (e)— — 66,234 66,234 
Total $852,239 $1,633,969 $832,143 $3,318,351 
Other Benefits:    
Cash and cash equivalents$2,184 $— $— $2,184 
Fixed income securities:   
Corporate— 202,640 — 202,640 
U.S. Treasury353,650 — — 353,650 
Other (b)— 7,999 — 7,999 
Common stock equities (c)146,316 — — 146,316 
Mutual funds (d)14,351 — — 14,351 
Common and collective trusts:
   Equities— — 83,648 83,648 
   Real estate— — 19,806 19,806 
Short-term investments and other (e)2,881 — 4,019 6,900 
Total $519,382 $210,639 $107,473 $837,494 
(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.
(c)This category primarily consists of U.S. common stock equities.
(d)These funds invest in U.S. and international common stock equities.
(e)This category 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
2021$210,119 $31,204 
2022209,593 31,731 
2023215,527 32,196 
2024220,241 31,914 
2025220,787 31,484 
Years 2026-20301,116,848 153,536