Fair Value Measurements - Schedule of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
ASSETS
Cash equivalents	$ 1	$ 23
Nuclear decommissioning trusts:	1,393,446	1,282,845
Nuclear decommissioning trust, other	489,772	426,404
Other special use funds:	429,932	408,357
Other special use funds, other	2,167	2,851
Total assets	1,845,615	1,707,783
Total assets, other	480,363	425,485
Commodity contracts
ASSETS
Commodity contracts	22,236	16,558
Commodity contracts, other	(11,576)	(3,770)
LIABILITIES
Derivative instruments, other	5,785	817
Amounts Reported on Balance Sheets	(39,078)	(61,786)
Equity securities
ASSETS
Nuclear decommissioning trusts:	21,241	15,736
Nuclear decommissioning trust, other	2,091	3,335
Other special use funds:	105,521	27,813
Other special use funds, other	2,167	2,851
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	487,681	423,069
U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	352,998	367,396
Other special use funds:	324,411	355,544
Corporate debt
ASSETS
Nuclear decommissioning trusts:	237,191	203,180
Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	232,657	208,533
Municipal bonds
ASSETS
Nuclear decommissioning trusts:	37,785	37,429
Other fixed income
ASSETS
Nuclear decommissioning trusts:	23,893	27,502
Cash equivalents
ASSETS
Other special use funds:		25,000
Other special use funds, other		0
Level 1
ASSETS
Cash equivalents	1	23
Nuclear decommissioning trusts:	372,148	379,255
Other special use funds:	427,765	405,506
Total assets	799,914	784,784
Level 1 | Pinnacle West Captive Insurance Cell
ASSETS
Other special use funds:	39,400	34,200
Level 1 | Commodity contracts
ASSETS
Commodity contracts	0	0
LIABILITIES
Derivative instruments	0	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trusts:	19,150	11,859
Other special use funds:	103,354	24,962
Level 1 | Equity securities | Pinnacle West Captive Insurance Cell
ASSETS
Other special use funds:		9,200
Level 1 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	352,998	367,396
Other special use funds:	324,411	355,544
Level 1 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	0	0
Level 1 | Cash equivalents
ASSETS
Other special use funds:		25,000
Level 1 | Cash equivalents | Pinnacle West Captive Insurance Cell
ASSETS
Other special use funds:		25,000
Level 2
ASSETS
Cash equivalents	0	0
Nuclear decommissioning trusts:	531,526	477,186
Other special use funds:	0	0
Total assets	563,969	490,338
Level 2 | Commodity contracts
ASSETS
Commodity contracts	32,443	13,152
LIABILITIES
Derivative instruments	(25,218)	(40,388)
Level 2 | Equity securities
ASSETS
Nuclear decommissioning trusts:	0	542
Other special use funds:	0	0
Level 2 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 2 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds:	0	0
Level 2 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	237,191	203,180
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	232,657	208,533
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	37,785	37,429
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	23,893	27,502
Level 2 | Cash equivalents
ASSETS
Other special use funds:		0
Level 3
ASSETS
Cash equivalents	0	0
Nuclear decommissioning trusts:	0	0
Other special use funds:	0	0
Total assets	1,369	7,176
Level 3 | Commodity contracts
ASSETS
Commodity contracts	1,369	7,176
LIABILITIES
Derivative instruments	(19,645)	(22,215)
Level 3 | Equity securities
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds:	0	0
Level 3 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trusts:	0	0
Other special use funds:	0	0
Level 3 | Corporate debt
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Municipal bonds
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Other fixed income
ASSETS
Nuclear decommissioning trusts:	0	0
Level 3 | Cash equivalents
ASSETS
Other special use funds:		0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trusts:		$ 423,069
Nuclear decommissioning trust, other	$ 487,681