Regulatory Matters (Details) - APS												2 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Feb. 01, 2016 $ / kWh	Jan. 15, 2016 USD ($)	Jun. 01, 2015 USD ($)	Mar. 02, 2015 USD ($)	Feb. 01, 2015 $ / kWh	Jun. 01, 2014 USD ($)	Apr. 15, 2014 Customer MW	Mar. 01, 2014 USD ($)	Jan. 01, 2014 USD ($) $ / kWh	Jan. 06, 2012 USD ($) $ / kWh	Jun. 01, 2011 USD ($)	Apr. 30, 2014 workshop	Jan. 31, 2016 $ / kWh	Sep. 30, 2015 $ / kWh	Dec. 31, 2015 $ / kWh	Jul. 01, 2015 USD ($)	Mar. 20, 2015 USD ($) project	Dec. 31, 2014 USD ($)	Dec. 19, 2014 MW	Jul. 01, 2014 USD ($)	Mar. 11, 2014 USD ($)	Dec. 31, 2012 USD ($)	Jun. 01, 2012
Lost Fixed Cost Recovery Mechanism
Settlement Agreement
Rate matter cap percentage of retail revenue															1.00%
ACC | Electric Energy Efficiency Standard
Settlement Agreement
Public utilities, cost effective energy efficiency programs, number of workshops | workshop												3
ACC | Net Metering
Settlement Agreement
Charge on future customers who install rooftop solar panels (in dollars per kWh) | $ / kWh									0.70					0.70
Estimated monthly collection due to charge on future customers who install rooftop solar panels									$ 4.90
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				$ 25,300,000
Cost Recovery Mechanisms | ACC | 2013 DSMAC
Settlement Agreement
Amount of proposed budget																						$ 87,600,000
Amount of approved budget																					$ 68,900,000
Rate matter, cumulative energy savings for current year percentage																							5.00%
Cost Recovery Mechanisms | ACC | 2014 DSMAC
Settlement Agreement
Amount of approved budget																					$ 68,900,000
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 | 2016 DSMAC
Settlement Agreement
Amount of proposed budget			$ 68,900,000
Rate matter, proposed rate reduction percentage			12.00%
Cost Recovery Mechanisms | ACC | RES
Settlement Agreement
Plan term															5 years
Cost Recovery Mechanisms | ACC | RES implementation plan covering 2014-2018 timeframe
Settlement Agreement
Amount of proposed budget																				$ 154,000,000
Amount of approved budget																		$ 152,000,000
Cost Recovery Mechanisms | ACC | Arizona Renewable Energy Standard and Tariff 2016
Settlement Agreement
Amount of proposed budget																$ 148,000,000
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					0.000887
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)			$ 5,900,000
AZ Sun Program | Filing with the Arizona Corporation Commission | Arizona Renewable Energy Standard and Tariff 2014
Settlement Agreement
Rate matter additional capacity from AZ Sun projects | MW							20
Alternative to AZ Sun Program | Filing with the Arizona Corporation Commission | Arizona Renewable Energy Standard and Tariff 2014
Settlement Agreement
Rate matter additional capacity from AZ Sun projects | MW							10
Request to build additional utility scale solar, number of customers | Customer							1,500
Alternative to AZ Sun Program, Phase 1 | Filing with the Arizona Corporation Commission | 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 | Filing with the Arizona Corporation Commission | Arizona Renewable Energy Standard and Tariff 2014
Settlement Agreement
Rate matter additional capacity from AZ Sun projects | MW																			2
Subsequent Event | Cost Recovery Mechanisms | Lost Fixed Cost Recovery Mechanism
Settlement Agreement
Amount of adjustment representing prorated sales losses pending approval		$ 46,400,000
Increase in Amount of Adjustment Representing Prorated Sales Losses		$ 7,900,000
Subsequent Event | Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA)
Settlement Agreement
PSA rate (in dollars per kWh) | $ / kWh	0.001678
Forward component of PSA rate (in dollars per kWh) | $ / kWh	0.001975
Historical component of PSA rate (in dollars per kWh) | $ / kWh	(0.000297)
Transition component of PSA rate (in dollars per KWh) | $ / kWh													(0.004936)