REGULATORY MATTERS (2019 ACC Rate Case) (Details) - Arizona Corporation Commission $ in Millions	1 Months Ended
	Apr. 30, 2019 USD ($)
Non-fuel Component of Base Rate
Public Utilities, General Disclosures [Line Items]
Non-fuel base rate increase (decrease)	$ 99
Original cost rate base (percentage)	7.49%
Original cost rate base	$ 2,700
Original cost of equity (percentage)	10.00%
Average original cost of debt (percentage)	4.65%
Fuel Component of Base Rate
Public Utilities, General Disclosures [Line Items]
Non-fuel base rate increase (decrease)	$ (39)
Revenue Component of Base Rate
Public Utilities, General Disclosures [Line Items]
Non-fuel base rate increase (decrease)	$ 60