REGULATORY MATTERS (2017 Rate Order) (Details) - Arizona Corporation Commission $ in Millions	Sep. 20, 2018 $ / kWh	Feb. 27, 2017 USD ($)
Public Utilities, General Disclosures [Line Items]
Export rate (in usd per kWh) | $ / kWh	0.0964
Non-fuel Component of Base Rate
Public Utilities, General Disclosures [Line Items]
Non-fuel base rate increase over adjusted test year revenues | $		$ 81.5
Previous net metering rules, applicable, term (in years)	20 years
Term for export rate (in years)	10 years