Income Taxes - Components of Deferred Income Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
DEFERRED TAX ASSETS
Risk management activities	$ 25,103	$ 26,614
Regulatory liabilities:
Excess Deferred Income Taxes - Tax Cuts and Jobs Act	376,906	0
Asset retirement obligation and removal costs	135,847	200,140
Unamortized investment tax credits	54,661	113,195
Other postretirement liabilities	47,021	60,375
Other	37,489	63,311
Pension liabilities	83,126	204,436
Renewable energy incentives	33,546	56,379
Credit and loss carryforwards	53,946	75,944
Other	102,432	158,421
Total deferred tax assets	950,077	958,815
DEFERRED TAX LIABILITIES
Plant-related	(2,220,886)	(3,297,989)
Risk management activities	(491)	(7,594)
Other postretirement assets	(66,134)	(63,477)
Regulatory assets:
Allowance for equity funds used during construction	(36,365)	(61,088)
Deferred fuel and purchased power — mark-to-market	(40,778)	(21,396)
Pension benefits	(142,848)	(274,184)
Retired power plant costs (see Note 3)	(53,611)	(49,166)
Other	(74,423)	(123,987)
Other	(5,346)	(5,166)
Total deferred tax liabilities	(2,640,882)	(3,904,047)
Deferred income taxes — net	(1,690,805)	(2,945,232)
ARIZONA PUBLIC SERVICE COMPANY
DEFERRED TAX ASSETS
Risk management activities	25,103	26,614
Regulatory liabilities:
Excess Deferred Income Taxes - Tax Cuts and Jobs Act	376,906	0
Asset retirement obligation and removal costs	135,847	200,140
Unamortized investment tax credits	54,661	113,195
Other postretirement liabilities	47,021	60,375
Other	37,489	63,311
Pension liabilities	77,280	194,981
Renewable energy incentives	33,546	56,379
Credit and loss carryforwards	1,920	1,645
Other	108,223	187,453
Total deferred tax assets	897,996	904,093
DEFERRED TAX LIABILITIES
Plant-related	(2,220,886)	(3,297,989)
Risk management activities	(491)	(7,594)
Other postretirement assets	(65,733)	(62,819)
Regulatory assets:
Allowance for equity funds used during construction	(36,365)	(61,088)
Deferred fuel and purchased power — mark-to-market	(40,778)	(21,396)
Pension benefits	(142,848)	(274,184)
Retired power plant costs (see Note 3)	(53,611)	(49,166)
Other	(74,423)	(123,987)
Other	(5,346)	(5,165)
Total deferred tax liabilities	(2,640,481)	(3,903,388)
Deferred income taxes — net	$ (1,742,485)	$ (2,999,295)