Income Taxes - Schedule of Components of the Net Deferred Income Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
DEFERRED TAX ASSETS
Risk management activities	$ 8,422	$ 14,539
Regulatory liabilities:
Excess deferred income taxes — Tax Cuts and Jobs Act	259,000	271,004
Asset retirement obligation and removal costs	66,031	81,308
Unamortized investment tax credits	81,949	66,327
Other postretirement benefits	57,833	58,862
Other	50,611	47,671
Operating lease liabilities	923,774	400,771
Pension liabilities	46,613	39,070
Coal reclamation liabilities	39,450	42,391
Renewable energy incentives	11,908	14,571
Credit and loss carryforwards	0	7,682
Employee benefit liabilities	56,447	57,853
Other	49,098	44,412
Total deferred tax assets	1,651,136	1,146,461
DEFERRED TAX LIABILITIES
Plant-related	(2,595,668)	(2,562,990)
Risk management activities	(2,072)	(4,089)
Pension and other postretirement assets	(97,557)	(83,401)
Other special use funds	(58,175)	(55,146)
Operating lease right-of-use assets	(923,774)	(400,771)
Regulatory assets:
Allowance for equity funds used during construction	(50,402)	(47,694)
Deferred fuel and purchased power	(45,504)	(84,393)
Pension benefits	(178,736)	(185,641)
Retired power plant costs	(13,157)	(16,904)
Other	(58,822)	(57,602)
Other	(54,418)	(43,383)
Total deferred tax liabilities	(4,122,068)	(3,590,934)
Deferred income taxes — net	(2,470,932)	(2,444,473)
Ocotillo deferral
Regulatory assets:
Deferral	(24,703)	(28,372)
SCR deferral
Regulatory assets:
Deferral	(19,080)	(20,548)
APS
DEFERRED TAX ASSETS
Risk management activities	8,422	14,539
Regulatory liabilities:
Excess deferred income taxes — Tax Cuts and Jobs Act	259,000	271,004
Asset retirement obligation and removal costs	66,031	81,308
Unamortized investment tax credits	81,949	66,327
Other postretirement benefits	57,833	58,862
Other	50,611	47,671
Operating lease liabilities	923,479	400,442
Pension liabilities	43,422	36,100
Coal reclamation liabilities	39,450	42,391
Renewable energy incentives	11,908	14,571
Credit and loss carryforwards	0	0
Employee benefit liabilities	55,243	56,561
Other	49,098	44,412
Total deferred tax assets	1,646,446	1,134,188
DEFERRED TAX LIABILITIES
Plant-related	(2,595,668)	(2,562,990)
Risk management activities	(2,072)	(4,089)
Pension and other postretirement assets	(96,988)	(82,925)
Other special use funds	(58,175)	(55,146)
Operating lease right-of-use assets	(923,479)	(400,443)
Regulatory assets:
Allowance for equity funds used during construction	(50,402)	(47,694)
Deferred fuel and purchased power	(45,504)	(84,393)
Pension benefits	(178,736)	(185,641)
Retired power plant costs	(13,157)	(16,904)
Other	(58,822)	(57,602)
Other	(7,425)	(7,378)
Total deferred tax liabilities	(4,074,211)	(3,554,125)
Deferred income taxes — net	$ (2,427,765)	$ (2,419,937)