FAIR VALUE MEASUREMENTS (Level 3 Reconciliation) (Details) - Level 3 - Price Risk Management Instruments - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning asset (liability) balance	$ (18)	$ (66)	$ (72)	$ 5
Net realized and unrealized gains (losses):
Included in regulatory assets and liabilities or balancing accounts	(62)	(31)	(8)	(102)
Ending asset (liability) balance	$ (80)	$ (97)	$ (80)	$ (97)