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Regulatory Matters - Retail Rate Case Filing (Details) - Retail Rate Case Filing with Arizona Corporation Commission - ACC - APS | Jan. 03, 2018 Customer | Nov. 13, 2017 USD ($) | Mar. 27, 2017 USD ($) $ / kWh | Mar. 26, 2017 $ / kWh | Jun. 01, 2016 USD ($) | Dec. 31, 2015 USD ($) | Jun. 01, 2011 USD ($) | Jun. 30, 2018 appeal
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Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Net retail rate increase |  |  |  |  | $ 165,900,000 |  | $ 95,500,000 |
Adjustor account balance transferred into base rates, amount |  |  |  |  |  | $ 267,600,000 |  |
Approximate percentage of increase in average customer bill |  |  | 3.28% |  | 5.74% |  |  |
Approximate percentage of increase in average residential customer bill | 4.54% |  | 4.54% |  | 7.96% |  |  |
Net retail base rate, increase |  |  | $ 94,600,000 |  |  |  |  |
Non-fuel and non-depreciation base rate, increase |  |  | 87,200,000 |  |  |  |  |
Fuel-related base rate decrease |  |  | 53,600,000 |  |  |  |  |
Base rate increase, changes in depreciation schedules |  |  | $ 61,000,000 |  |  |  |  |
Authorized return on common equity (as a percent) |  |  | 10.00% |  |  |  |  |
Percentage of debt in capital structure |  |  | 44.20% |  |  |  |  |
Percentage of common equity in capital structure |  |  | 55.80% |  |  |  |  |
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh |  |  | 0.00050 | 0.00016 |  |  |  |
Rate matter, resource comparison proxy for exported energy (in dollars per kWh) | $ / kWh |  |  | 0.129 |  |  |  |  |
Periodic metering infrastructure opt-out fee |  | $ 5 |  |  |  |  |  |
Number of appeals | appeal |  |  |  |  |  |  |  | 2
Number of customers named in complaint | Customer | 25 |  |  |  |  |  |  |
AZ Sun Program Phase 2 |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Public utilities, minimum annual renewable energy standard and tariff |  |  | $ 10,000,000 |  |  |  |  |
Public utilities, maximum annual renewable energy standard and tariff |  |  | $ 15,000,000 |  |  |  |  |

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