Regulatory Matters - Narrative (Details)																			1 Months Ended		2 Months Ended	12 Months Ended
	Feb. 22, 2018 USD ($)	Feb. 15, 2018 USD ($)	Feb. 09, 2018	Feb. 01, 2018 $ / kWh	Jan. 08, 2018 USD ($)	Nov. 20, 2017 USD ($)	Aug. 19, 2017 $ / kWh	Jun. 01, 2017 USD ($)	Feb. 01, 2017 $ / kWh	Jan. 13, 2017 USD ($)	Dec. 20, 2016 $ / kWh	Jun. 01, 2016 USD ($)	Feb. 01, 2016 $ / kWh	Jan. 15, 2016 USD ($)	Jan. 01, 2016 USD ($)	Feb. 01, 2015 $ / kWh	Nov. 04, 2014	Jun. 01, 2011 USD ($)	Sep. 30, 2016	Dec. 31, 2014 penetration_feeder storage_system MW	Apr. 30, 2014 workshop	Dec. 31, 2017 USD ($) $ / kWh	Dec. 31, 2012 $ / kWh	Nov. 14, 2017 USD ($)	Sep. 01, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jan. 27, 2017 USD ($)	Jul. 01, 2016 USD ($)	Nov. 25, 2015 USD ($)	Mar. 20, 2015 project
APS
Regulatory Matters [Line Items]
Requested rate decrease for tax act																						$ (377,000,000)
APS | Lost Fixed Cost Recovery Mechanism
Regulatory Matters [Line Items]
Fixed costs recoverable per residential power lost (in dollars per kWh) | $ / kWh																							0.031
Fixed costs recoverable per non-residential power lost (in dollars per kWh) | $ / kWh																							0.023
Fixed costs recoverable per power lost (in dollars per kWh) | $ / kWh																						0.025
Rate matter cap percentage of retail revenue																						1.00%
Amount of adjustment approved representing prorated sales losses										$ 63,700,000				$ 46,400,000
Increase in amount of adjustment representing prorated sales losses										$ 17,300,000				$ 7,900,000
APS | ACC | Retail Rate Case Filing with Arizona Corporation Commission
Regulatory Matters [Line Items]
Net retail rate increase												$ 165,900,000						$ 95,500,000
Reduced system benefits charge, amount															$ 14,600,000
APS | ACC | Arizona Renewable Energy Standard and Tariff
Regulatory Matters [Line Items]
Plan term																						5 years
APS | ACC | Arizona Renewable Energy Standard and Tariff 2017
Regulatory Matters [Line Items]
Amount of approved budget																												$ 150,000,000
APS | ACC | Arizona Renewable Energy Standard and Tariff 2018
Regulatory Matters [Line Items]
Amount of proposed budget																										$ 90,000,000
APS | ACC | Modernization and Expansion of the Renewal Energy Standard
Regulatory Matters [Line Items]
Proposed renewal energy standard, percent of retail sales																			30.00%
Current renewal energy standard, percent of retail sales																			15.00%
APS | ACC | 2015 DSMAC
Regulatory Matters [Line Items]
Amount of approved budget																													$ 68,900,000
Rate matter number of resource savings projects | project																														3
APS | ACC | 2017 DSMAC
Regulatory Matters [Line Items]
Amount of approved budget																											$ 66,600,000
Amount of proposed budget												62,600,000
APS | ACC | Demand Side Management Adjustor Charge 2018
Regulatory Matters [Line Items]
Amount of proposed budget																								$ 52,600,000	$ 52,600,000
APS | ACC | Electric Energy Efficiency Standard
Regulatory Matters [Line Items]
Public utilities, cost effective energy efficiency programs, number of workshops | workshop																					3
Public utilities, cost effective efficiency programs, number of days to convene a workshop																	120 days
APS | ACC | Power Supply Adjustor (PSA)
Regulatory Matters [Line Items]
PSA rate (in dollars per kWh) | $ / kWh							0.000555		(0.001348)
Forward component of PSA rate (in dollars per kWh) | $ / kWh							0.000876		(0.001027)
Historical component of PSA rate (in dollars per kWh) | $ / kWh							(0.000321)		(0.000321)
APS | ACC | Net Metering
Regulatory Matters [Line Items]
Cost of service, resource comparison proxy method, maximum annual percentage decrease											10.00%
Cost of service for interconnected DG system customers, grandfathered period											20 years
Guaranteed export price period											10 years
Settlement agreement, energy price for exported energy (in dollars per kWh) | $ / kWh											0.129
APS | FERC | Transmission rates, transmission cost adjustor and other transmission matters
Regulatory Matters [Line Items]
Increase (decrease) in annual wholesale transmission rates								$ 35,100,000				$ 24,900,000
Cost Recovery Mechanisms | APS | ACC | Power Supply Adjustor (PSA)
Regulatory Matters [Line Items]
Maximum increase (decrease) in PSA rate (in dollars per kWh) | $ / kWh																0.004
PSA Rate in Prior Years | $ / kWh													0.001678
Subsequent Event
Regulatory Matters [Line Items]
Ballot initiative, proposed required energy supply to be obtained from renewable sources (as a percent)			50.00%
Subsequent Event | APS | Lost Fixed Cost Recovery Mechanism
Regulatory Matters [Line Items]
Increase in amount of adjustment representing prorated sales losses		$ 3,000,000
Amount of adjustment approved representing prorated sales losses pending approval		$ 60,700,000
Subsequent Event | APS | ACC
Regulatory Matters [Line Items]
Requested rate decrease for tax act					$ 119,100,000
Approved rate decrease for tax act	$ 119,100,000
Subsequent Event | APS | ACC | Power Supply Adjustor (PSA)
Regulatory Matters [Line Items]
PSA rate (in dollars per kWh) | $ / kWh				0.004555
Forward component of PSA rate (in dollars per kWh) | $ / kWh				0.002009
Historical component of PSA rate (in dollars per kWh) | $ / kWh				0.002546
Alternative to AZ Sun Program, Phase 1 | APS | Arizona Renewable Energy Standard and Tariff 2014
Regulatory Matters [Line Items]
Rate matter additional capacity from AZ Sun projects | MW																				8
Solar Partner Program Phase 2 | APS | Arizona Renewable Energy Standard and Tariff 2014
Regulatory Matters [Line Items]
Rate matter additional capacity from AZ Sun projects | MW																				2
Solar storage system, capacity (in MW) | MW																				2
Number of energy storage systems | storage_system																				2
Number of high solar penetration feeders | penetration_feeder																				2
Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018
Regulatory Matters [Line Items]
Program term						3 years
Minimum | Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018
Regulatory Matters [Line Items]
Required annual capital investment						$ 10,000,000
Maximum | Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018
Regulatory Matters [Line Items]
Required annual capital investment						$ 15,000,000