Income Taxes - Components of Deferred Income Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
DEFERRED TAX ASSETS
Risk management activities	$ 4,287	$ 17,552
Regulatory liabilities:
Excess deferred income taxes — Tax Cuts and Jobs Act	319,091	335,877
Asset retirement obligation and removal costs	157,470	143,011
Unamortized investment tax credits	50,879	52,236
Other postretirement liabilities	95,778	43,841
Other	43,551	52,382
Operating lease liabilities	107,853	15,497
Pension liabilities	45,853	73,210
Coal reclamation liabilities	42,065	40,837
Renewable energy incentives	25,355	28,066
Credit and loss carryforwards	26,460	54,795
Other	78,113	47,605
Total deferred tax assets	996,755	904,909
DEFERRED TAX LIABILITIES
Plant-related	(2,489,899)	(2,448,458)
Risk management activities	(1,174)	(27)
Pension and other postretirement assets	(123,462)	(21,892)
Other special use funds	(42,927)	(44,507)
Operating lease right-of-use assets	(107,853)	(15,497)
Regulatory assets:
Allowance for equity funds used during construction	(41,038)	(40,023)
Deferred fuel and purchased power	(47,673)	(35,162)
Pension benefits	(116,219)	(163,339)
Retired power plant costs	(35,214)	(42,228)
Other	(106,227)	(82,722)
Other	(20,472)	(3,393)
Total deferred tax liabilities	(3,132,158)	(2,897,248)
Deferred income taxes — net	(2,135,403)	(1,992,339)
ARIZONA PUBLIC SERVICE COMPANY
DEFERRED TAX ASSETS
Risk management activities	4,287	17,552
Regulatory liabilities:
Excess deferred income taxes — Tax Cuts and Jobs Act	319,091	335,877
Asset retirement obligation and removal costs	157,470	143,011
Unamortized investment tax credits	50,879	52,236
Other postretirement liabilities	95,778	43,841
Other	43,551	52,382
Operating lease liabilities	107,414	15,497
Pension liabilities	40,168	67,976
Coal reclamation liabilities	42,065	40,837
Renewable energy incentives	25,355	28,066
Credit and loss carryforwards	8,034	10,992
Other	78,113	55,451
Total deferred tax assets	972,205	863,718
DEFERRED TAX LIABILITIES
Plant-related	(2,489,899)	(2,448,458)
Risk management activities	(1,174)	(27)
Pension and other postretirement assets	(122,580)	(21,458)
Other special use funds	(42,927)	(44,507)
Operating lease right-of-use assets	(107,414)	(15,497)
Regulatory assets:
Allowance for equity funds used during construction	(41,038)	(40,023)
Deferred fuel and purchased power	(47,673)	(35,162)
Pension benefits	(116,219)	(163,339)
Retired power plant costs	(35,214)	(42,228)
Other	(106,227)	(82,722)
Other	(5,513)	(3,393)
Total deferred tax liabilities	(3,115,878)	(2,896,814)
Deferred income taxes — net	$ (2,143,673)	$ (2,033,096)