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Regulatory Matters (Details) |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |  |
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Jun. 01, 2016 USD ($) | Feb. 01, 2016 $ / kWh | Jan. 15, 2016 USD ($) | Jan. 01, 2016 USD ($) | Jun. 01, 2015 USD ($) | Mar. 02, 2015 USD ($) | Nov. 04, 2014 | Mar. 01, 2014 USD ($) | Jan. 01, 2014 USD ($) $ / kWh | Jan. 06, 2012 USD ($) $ / kWh | Sep. 30, 2016 USD ($) phase | Dec. 31, 2014 USD ($) penetration_feeder storage_system MW | Apr. 30, 2014 workshop | Jan. 31, 2016 $ / kWh | Sep. 30, 2016 USD ($) $ / kWh | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($) $ / kWh | Jul. 12, 2016 USD ($) | Jul. 01, 2016 USD ($) | Apr. 01, 2016 USD ($) | Jan. 12, 2016 USD ($) | Nov. 25, 2015 USD ($) | Mar. 20, 2015 project
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 46,185,000 | $ 137,000 |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (28,366,000) | (19,284,000) |  |  |  |  |  |  |
APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46,185,000 | 137,000 |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (28,366,000) | (19,284,000) |  |  |  |  |  |  |
RES 2014 | APS | Alternative to AZ Sun Program, Phase 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request to build additional utility scale solar, capacity | MW |  |  |  |  |  |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |  |  |  |
RES 2014 | APS | Alternative to AZ Sun Program Phase 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request to build additional utility scale solar, capacity | MW |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |
Number of energy storage systems | storage_system |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |
Number of high solar penetration feeders | penetration_feeder |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |
Lost Fixed Cost Recovery Mechanisms | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |
Percentage of retail revenues |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  | 1.00% |  |  |  |  |  |  |  |
Amount of adjustment representing prorated sales losses approval |  |  | $ 46,400,000 |  |  | $ 38,500,000 |  | $ 25,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in amount of adjustment representing prorated sales losses |  |  | $ 7,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Retail Rate Case Filing with Arizona Corporation Commission | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduced system benefits charge, amount |  |  |  | $ 14,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Retail Rate Case Filing with Arizona Corporation Commission | APS | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual cost recovery due to modifications to the Environmental Improvement Surcharge |  |  |  |  |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | RES | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plan term |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
ACC | RES 2016 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 148,000,000 |  |
ACC | RES 2017 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |  |
ACC | Modernization and Expansion of the Renewal Energy Standard [Member] | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed renewal energy standard, percent of retail sales |  |  |  |  |  |  |  |  |  |  | 30.00% |  |  |  |  |  |  |  |  |  |  |  |
Current renewal energy standard, percent of retail sales |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  |  |  |  |  |  |  |  |  |
ACC | DSMAC 2015 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 68,900,000 |  | $ 68,900,000 |
Additional budget approved |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,000,000 |  |  |  |  |
Number of resource savings projects | project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3
ACC | DSMC 2016 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  | $ 68,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Electric energy efficiency standard | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of workshops | workshop |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |
Number of days to convene a workshop |  |  |  |  |  |  | 120 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Power Supply Adjustor (PSA) | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | $ (9,688,000) |  |  |  |  |  |  |  |  |  |  | $ (9,688,000) | 6,925,000 | $ 6,925,000 |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46,185,000 | 137,000 |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (28,365,000) | (19,284,000) |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | $ 8,132,000 | $ 6,925,000 |  |  | $ 8,132,000 | $ (12,222,000) | $ (9,688,000) |  |  |  |  |  |
PSA rate (in dollars per kWh) | $ / kWh |  | 0.001678 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA rate for prior year (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.000887 |  |  |  |  |  |
Forward component of increase in PSA (in dollars per kWh) | $ / kWh |  | 0.001975 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Historical component of increase in PSA (in dollars per kWh) | $ / kWh |  | (0.000297) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Transition component increase in PSA (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  | (0.004936) |  |  |  |  |  |  |  |  |
ACC | Net Metering | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Charge on future customers who install rooftop solar panels (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  | 0.70 |  |  |  |  |  | 0.70 |  |  |  |  |  |  |  |
Rate matter case, umber of filing phases | phase |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |
Estimated monthly collection due to charge on future customers who install rooftop solar panels |  |  |  |  |  |  |  |  | $ 4.90 |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States Federal Energy Regulatory Commission | Open Access Transmission Tariff [Member] | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in annual wholesale transmission rates |  |  |  |  | $ 17,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in annual wholesale transmission rates | $ 24,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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