FAIR VALUE MEASUREMENTS (Level 3 Reconciliation) (Details) - Level 3 - Price Risk Management Instruments - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning asset (liability) balance	$ (66)	$ 109	$ 5	$ 95
Net Realized and Unrealized Gains (Losses) [Abstract]
Included in regulatory assets and liabilities or balancing accounts	(31)	(75)	(102)	(61)
Ending asset (liability) balance	$ (97)	$ 34	$ (97)	$ 34