Regulatory Matters - Retail Rate Case Filing (Details) - ACC - APS										12 Months Ended
	Oct. 31, 2019 USD ($) GW	Jun. 30, 2019 USD ($)	Apr. 10, 2019 USD ($)	Aug. 13, 2018 USD ($)	Feb. 13, 2018	Jan. 08, 2018 USD ($)	Jan. 03, 2018 Customer	Nov. 13, 2017 USD ($) appeal	Mar. 27, 2017 USD ($) $ / kWh	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount, Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)			$ 184,000,000	$ (86,500,000)		$ (119,100,000)
Retail Rate Case Filing with Arizona Corporation Commission
Public Utilities, General Disclosures [Line Items]
Approximate percentage of increase in average customer bill									3.28%
Rate matter, cost base rate		$ 8,870,000,000
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									$ 61,000,000.0
Approximate percentage of increase in average residential customer bill					4.54%				4.54%
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, 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 | Retail Rate Case Filing with Arizona Corporation Commission
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
Minimum | Retail Rate Case Filing with Arizona Corporation Commission
Public Utilities, General Disclosures [Line Items]
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh									0.00016
Maximum | Retail Rate Case Filing with Arizona Corporation Commission
Public Utilities, General Disclosures [Line Items]
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh									0.00050
Subsequent Event | Retail Rate Case Filing with Arizona Corporation Commission
Public Utilities, General Disclosures [Line Items]
Retail base rate, increase	$ 0.054
Base rate decrease, elimination of tax expense adjustment mechanism	$ 115,000,000
Approximate percentage of increase in average customer bill	5.60%
Funding limited income crisis bill program	$ 1,250,000
Commercial customers, market pricing, threshold | GW	0.2
Forecast
Public Utilities, General Disclosures [Line Items]
Operating Results										$ (10,000,000)
Forecast | Minimum
Public Utilities, General Disclosures [Line Items]
Operating Results	$ 69,000,000