Regulatory Matters (Details) - APS															1 Months Ended		2 Months Ended	12 Months Ended
	Feb. 01, 2017 $ / kWh	Jan. 13, 2017 USD ($)	Dec. 20, 2016	Jul. 12, 2016 USD ($)	Jun. 01, 2016 USD ($) kWh $ / kWh	Feb. 01, 2016 $ / kWh	Jan. 15, 2016 USD ($)	Jan. 01, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 01, 2015 USD ($)	Mar. 02, 2015 USD ($)	Feb. 01, 2015 $ / kWh	Jan. 06, 2012 USD ($) $ / kWh	Jun. 01, 2011 USD ($)	Sep. 30, 2016	Dec. 31, 2014 storage_system penetration_feeder MW	Apr. 30, 2014 workshop	Dec. 31, 2016 $ / kWh	Jan. 27, 2017 USD ($)	Dec. 05, 2016 USD ($)	Jul. 01, 2016 USD ($)	Apr. 01, 2016 USD ($)	Jul. 01, 2015 USD ($)	Mar. 20, 2015 USD ($) project
Lost Fixed Cost Recovery Mechanism
Settlement Agreement
Rate matter cap percentage of retail revenue																		1.00%
ACC | 2016 DSMAC
Settlement Agreement
Amount of approved budget										$ 68,900,000												$ 68,900,000
Additional approved budget				$ 4,000,000
ACC | 2017 DSMAC
Settlement Agreement
Amount of proposed budget					$ 62,600,000
ACC | Residential demand response, energy storage and load management program
Settlement Agreement
Additional approved budget																				$ 4,000,000
ACC | Electric Energy Efficiency Standard
Settlement Agreement
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
ACC | Modernization and Expansion of the Renewal Energy Standard
Settlement Agreement
Proposed renewal energy standard, percent of retail sales															30.00%
Current renewal energy standard, percent of retail sales															15.00%
ACC | Net Metering
Settlement Agreement
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
Rate matters, cost of service for new customers, guaranteed export price period			10 years
ACC | Retail Rate Case Filing with Arizona Corporation Commission
Regulatory Matters [Line Items]
Net retail rate increase					$ 165,900,000
Adjuster account balance transferred into base rates									$ 267,600,000
Approximate percentage of increase in average customer bill					5.74%
Approximate percentage of increase in average residential customer bill					7.96%
original cost rate base					$ 6,800,000,000
Required return on incremental fair value rate base above original cost rate base					1.00%
Base rate for fuel and purchased power costs | $ / kWh					0.029882
Decrease in base rate for fuel and purchased power costs | $ / kWh					0.03207
Plan option, non-partial requirements customers, maximum average monthly energy usage | kWh					600
Case completion term					12 months
Settlement Agreement
Reduced system benefits charge, amount								$ 14,600,000
FERC | Transmission rates, transmission cost adjustor and other transmission matters
Settlement Agreement
Increase (decrease) in annual wholesale transmission rates					$ 24,900,000
Filing with the Arizona Corporation Commission | ACC | Retail rate case filing
Regulatory Matters [Line Items]
Net retail rate increase														$ 95,500,000
Approximate percentage of increase in the average retail customer bill														6.60%
Settlement Agreement
Net change in base rates													$ 0
Non-fuel base rate increase													116,300,000
Fuel-related base rate decrease													$ 153,100,000
Current base fuel rate (in dollars per kWh) | $ / kWh													0.03757
Approved base fuel rate (in dollars per kWh) | $ / kWh													0.03207
Estimated amount of transfer of cost recovery for certain renewable energy projects from the RES surcharge to base rates													$ 36,800,000
Authorized return on common equity (as a percent)													10.00%
Percentage of debt in capital structure													46.10%
Percentage of common equity in capital structure													53.90%
Deferral of property taxes in 2012, if Arizona property tax rates increase (as a percent)													25.00%
Deferral of property taxes in 2013, if Arizona property tax rates increase (as a percent)													50.00%
Deferral of property taxes for 2014 and subsequent years, if Arizona property tax rates increase (as a percent)													75.00%
Deferral of property taxes in all years, if Arizona property tax rates decrease (as a percent)													100.00%
Elimination of the sharing provision of fuel and purchased power costs													9
Period to process the subsequent rate cases													12 months
ACC staff sufficiency findings, general period of time													30 days
Filing with the Arizona Corporation Commission | ACC | Retail rate case filing | Maximum
Settlement Agreement
Annual cost recovery due to modifications to the Environmental Improvement Surcharge													$ 5,000,000
Cost Recovery Mechanisms | Lost Fixed Cost Recovery Mechanism
Settlement Agreement
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
Amount of adjustment approved representing prorated sales losses											$ 38,500,000
Amount of adjustment representing prorated sales losses pending approval							$ 46,400,000
Increase in amount of adjustment representing prorated sales losses							$ 7,900,000
Cost Recovery Mechanisms | ACC | 2015 DSMAC
Settlement Agreement
Amount of proposed budget																								$ 68,900,000
Rate matter number of resource savings projects | project																								3
Cost Recovery Mechanisms | ACC | RES
Settlement Agreement
Plan term																		5 years
Cost Recovery Mechanisms | ACC | Arizona Renewable Energy Standard and Tariff 2016
Settlement Agreement
Amount of proposed budget																							$ 148,000,000
Cost Recovery Mechanisms | ACC | Arizona Renewable Energy Standard and Tariff 2017
Settlement Agreement
Amount of proposed budget																					$ 150,000,000
Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA)
Settlement Agreement
Maximum increase (decrease) in PSA rate (in dollars per kWh) | $ / kWh												0.004
PSA rate (in dollars per kWh) | $ / kWh						0.001678
Cost Recovery Mechanisms | FERC | Transmission rates, transmission cost adjustor and other transmission matters
Settlement Agreement
Increase (decrease) in annual wholesale transmission rates										$ (17,600,000)
Subsequent Event | ACC | 2017 DSMAC
Settlement Agreement
Amount of proposed budget																			$ 66,600,000
Subsequent Event | ACC | Power Supply Adjustor (PSA)
Settlement Agreement
PSA rate (in dollars per kWh) | $ / kWh	(0.001348)
Forward component of PSA rate (in dollars per kWh) | $ / kWh	(0.001027)
Historical component of PSA rate (in dollars per kWh) | $ / kWh	(0.000321)
Subsequent Event | ACC | Retail Rate Case Filing with Arizona Corporation Commission
Regulatory Matters [Line Items]
Case completion extension term		33 days
Subsequent Event | Cost Recovery Mechanisms | Lost Fixed Cost Recovery Mechanism
Settlement Agreement
Amount of adjustment representing prorated sales losses pending approval		$ 63,700,000
Increase in amount of adjustment representing prorated sales losses		$ 17,300,000
Four Corners Power Plant | ACC | Retail Rate Case Filing with Arizona Corporation Commission
Regulatory Matters [Line Items]
Authorization to defer for potential future recovery of construction costs					400,000,000
Ocotillo Plant | ACC | Retail Rate Case Filing with Arizona Corporation Commission
Regulatory Matters [Line Items]
Authorization to defer for potential future recovery of construction costs					$ 500,000,000
Alternative to AZ Sun Program, Phase 1 | Arizona Renewable Energy Standard and Tariff 2014
Settlement Agreement
Rate matter additional capacity from AZ Sun projects | MW																8
Alternative to AZ Sun Program Phase 2 | Arizona Renewable Energy Standard and Tariff 2014
Settlement Agreement
Rate matter additional capacity from AZ Sun projects | MW																2
Number of energy storage systems | storage_system																2
Number of high solar penetration feeders | penetration_feeder																2