Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Nuclear decommissioning trust fund assets
Fair Value	$ 871,000	$ 779,586
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	21,813	11,213	$ 5,189
Realized losses	(13,146)	(10,106)	(6,225)
Proceeds from the sale of securities	542,246	633,410	478,813
Fair value of fixed income securities, summarized by contractual maturities
Total	871,000	779,586
Fixed income securities
Nuclear decommissioning trust fund assets
Fair Value	478,294
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	25,123
1 year - 5 years	102,783
5 years - 10 years	137,854
Greater than 10 years	212,534
Total	478,294
Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	446,277
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	24,668
1 year - 5 years	100,289
5 years - 10 years	129,239
Greater than 10 years	192,081
Total	446,277
Escrow Accounts
Nuclear decommissioning trust fund assets
Fair Value	32,017
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	455
1 year - 5 years	2,494
5 years - 10 years	8,615
Greater than 10 years	20,453
Total	32,017
ARIZONA PUBLIC SERVICE COMPANY
Nuclear decommissioning trust fund assets
Fair Value	871,000	779,586
Total Unrealized Gains	260,160	197,911
Total Unrealized Losses	(2,996)	(4,962)
Net receivables for securities purchases	109	795
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Proceeds from the sale of securities	542,246	633,410	$ 478,813
Fair value of fixed income securities, summarized by contractual maturities
Total	871,000	779,586
ARIZONA PUBLIC SERVICE COMPANY | Equity securities
Nuclear decommissioning trust fund assets
Fair Value	417,390	353,261
Total Unrealized Gains	248,623	188,091
Total Unrealized Losses	0	0
Fair value of fixed income securities, summarized by contractual maturities
Total	417,390	353,261
ARIZONA PUBLIC SERVICE COMPANY | Fixed income securities
Nuclear decommissioning trust fund assets
Fair Value	446,277	425,530
Total Unrealized Gains	11,537	9,820
Total Unrealized Losses	(2,996)	(4,962)
Fair value of fixed income securities, summarized by contractual maturities
Total	446,277	425,530
ARIZONA PUBLIC SERVICE COMPANY | Cash and cash equivalents
Nuclear decommissioning trust fund assets
Fair Value	7,224	0
Total Unrealized Gains	0	0
Total Unrealized Losses	0	0
Fair value of fixed income securities, summarized by contractual maturities
Total	$ 7,224	$ 0