FAIR VALUE MEASUREMENTS (Level 3 Reconciliation) (Details) - Level 3 - Price Risk Management Instruments - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning asset (liability) balance	$ (94)	$ (5)	$ (72)	$ 5
Net Realized and Unrealized Gains (Losses) [Abstract]
Included in regulatory assets and liabilities or balancing accounts	76	(61)	54	(71)
Ending asset (liability) balance	$ (18)	$ (66)	$ (18)	$ (66)