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Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
ASSETS    
Cash equivalents $ 23 $ 10
Nuclear decommissioning trust 1,282,845 1,201,246
Nuclear decommissioning trust, other 426,404 408,849
Other special use fund 408,357 362,781
Other special use funds, other 2,851 2,196
Total assets 1,707,783 1,570,845
Total assets, other 425,485 409,356
Commodity contracts    
ASSETS    
Commodity contracts, assets 16,558 6,808
Commodity contracts assets, other (3,770) (1,689)
LIABILITIES    
Derivative instruments, other 817 4,823
Derivative instruments, total (61,786) (123,888)
Equity securities    
ASSETS    
Nuclear decommissioning trust 15,736 10,297
Nuclear decommissioning trust, other 3,335 (767)
Other special use fund 27,813 43,187
Other special use funds, other 2,851 2,196
U.S. commingled equity funds    
ASSETS    
Nuclear decommissioning trust 423,069 409,616
U.S. Treasury debt    
ASSETS    
Nuclear decommissioning trust 367,396 319,734
Other special use fund 355,544 319,594
Corporate debt    
ASSETS    
Nuclear decommissioning trust 203,180 188,317
Mortgage-backed securities    
ASSETS    
Nuclear decommissioning trust 208,533 208,306
Municipal bonds    
ASSETS    
Nuclear decommissioning trust 37,429 59,323
Other fixed income    
ASSETS    
Nuclear decommissioning trust 27,502 5,653
Cash equivalents    
ASSETS    
Other special use fund 25,000  
Other special use funds, other 0  
Level 1    
ASSETS    
Cash equivalents 23 10
Nuclear decommissioning trust 379,255 330,798
Other special use fund 405,506 360,585
Total assets 784,784 691,393
Level 1 | Pinnacle West Captive Insurance Cell    
ASSETS    
Other special use fund 34,200  
Level 1 | Commodity contracts    
ASSETS    
Commodity contracts, assets 0 0
LIABILITIES    
Derivative instruments 0 0
Level 1 | Equity securities    
ASSETS    
Nuclear decommissioning trust 11,859 11,064
Other special use fund 24,962 40,991
Level 1 | Equity securities | Pinnacle West Captive Insurance Cell    
ASSETS    
Other special use fund 9,200  
Level 1 | U.S. commingled equity funds    
ASSETS    
Nuclear decommissioning trust 0 0
Level 1 | U.S. Treasury debt    
ASSETS    
Nuclear decommissioning trust 367,396 319,734
Other special use fund 355,544 319,594
Level 1 | Corporate debt    
ASSETS    
Nuclear decommissioning trust 0 0
Level 1 | Mortgage-backed securities    
ASSETS    
Nuclear decommissioning trust 0 0
Level 1 | Municipal bonds    
ASSETS    
Nuclear decommissioning trust 0 0
Level 1 | Other fixed income    
ASSETS    
Nuclear decommissioning trust 0 0
Level 1 | Cash equivalents    
ASSETS    
Other special use fund 25,000  
Level 1 | Cash equivalents | Pinnacle West Captive Insurance Cell    
ASSETS    
Other special use fund 25,000  
Level 2    
ASSETS    
Cash equivalents 0 0
Nuclear decommissioning trust 477,186 461,599
Other special use fund 0 0
Total assets 490,338 463,480
Level 2 | Commodity contracts    
ASSETS    
Commodity contracts, assets 13,152 1,881
LIABILITIES    
Derivative instruments (40,388) (127,016)
Level 2 | Equity securities    
ASSETS    
Nuclear decommissioning trust 542 0
Other special use fund 0 0
Level 2 | U.S. commingled equity funds    
ASSETS    
Nuclear decommissioning trust 0 0
Level 2 | U.S. Treasury debt    
ASSETS    
Nuclear decommissioning trust 0 0
Other special use fund 0 0
Level 2 | Corporate debt    
ASSETS    
Nuclear decommissioning trust 203,180 188,317
Level 2 | Mortgage-backed securities    
ASSETS    
Nuclear decommissioning trust 208,533 208,306
Level 2 | Municipal bonds    
ASSETS    
Nuclear decommissioning trust 37,429 59,323
Level 2 | Other fixed income    
ASSETS    
Nuclear decommissioning trust 27,502 5,653
Level 2 | Cash equivalents    
ASSETS    
Other special use fund 0  
Level 3    
ASSETS    
Cash equivalents 0 0
Nuclear decommissioning trust 0 0
Other special use fund 0 0
Total assets 7,176 6,616
Level 3 | Commodity contracts    
ASSETS    
Commodity contracts, assets 7,176 6,616
LIABILITIES    
Derivative instruments (22,215) (1,695)
Level 3 | Equity securities    
ASSETS    
Nuclear decommissioning trust 0 0
Other special use fund 0 0
Level 3 | U.S. commingled equity funds    
ASSETS    
Nuclear decommissioning trust 0 0
Level 3 | U.S. Treasury debt    
ASSETS    
Nuclear decommissioning trust 0 0
Other special use fund 0 0
Level 3 | Corporate debt    
ASSETS    
Nuclear decommissioning trust 0 0
Level 3 | Mortgage-backed securities    
ASSETS    
Nuclear decommissioning trust 0 0
Level 3 | Municipal bonds    
ASSETS    
Nuclear decommissioning trust 0 0
Level 3 | Other fixed income    
ASSETS    
Nuclear decommissioning trust 0 0
Level 3 | Cash equivalents    
ASSETS    
Other special use fund 0  
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds    
ASSETS    
Nuclear decommissioning trust $ 423,069 $ 409,616