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Regulatory Matters - Retail Rate Case Filing (Details) - Retail Rate Case Filing with Arizona Corporation Commission - ACC - APS $ in Millions | Jun. 01, 2016 USD ($) kWh $ / kWh | Dec. 31, 2015 USD ($) | Jun. 01, 2011 USD ($)
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Public Utilities, General Disclosures [Line Items] |  |  |
Net retail rate increase | $ 165.9 |  | $ 95.5
Adjustor account balance transferred into base rates, amount |  | $ 267.6 |
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 | $ 6,800.0 |  |
Required return on incremental fair value rate base above original cost rate base | 1.00% |  |
Base rate for fuel and purchased power costs (in dollars per kWh) | $ / kWh | 0.029882 |  |
Decrease in base rate for fuel and purchased power costs (in dollars per kWh) | $ / kWh | 0.03207 |  |
Plan option, non-partial requirements customers, maximum average monthly energy usage (in kWh) | kWh | 600 |  |
Public utilities, case completion term | 12 months |  |
Approximate percentage of increase in the average retail customer bill |  |  | 6.60%
Proposed Capital Structure and Costs of Capital |  |  |
Requested debt capital structure (as a percent) | 44.20% |  |
Requested debt cost of capital (as a percent) | 5.13% |  |
Requested equity capital structure (as a percent) | 55.80% |  |
Requested equity cost of capital (as a percent) | 10.50% |  |
Requested weighted-average cost of capital (as a percent) | 8.13% |  |
Four Corners Power Plant |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Authorization to defer for potential future recovery of construction costs | $ 400.0 |  |
Ocotillo Plant |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Authorization to defer for potential future recovery of construction costs | $ 500.0 |  |

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