REGULATORY MATTERS (2020 Rate Order) (Details) - Arizona Corporation Commission - Non-fuel Component of Base Rate $ in Millions	1 Months Ended
	Dec. 31, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Non-fuel base rate increase (decrease)	$ 58
Original cost rate base (percentage)	7.04%
Original cost rate base	$ 2,700
Original cost of equity (percentage)	9.15%
Average original cost of debt (percentage)	4.65%
Capital structure for rate making purposes, common equity (percentage)	53.00%
Capital structure for rate making purposes, long-term debt (percentage)	47.00%