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 ($)	Jun. 01, 2011 USD ($)
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