FAIR VALUE MEASUREMENTS (Level 3 Reconciliation) (Details) - Level 3 - Price Risk Management Instruments - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning asset balance	$ 5	$ 95
Net Realized and Unrealized Gains [Abstract]
Included in regulatory assets and liabilities or balancing accounts	(10)	34
Ending asset balance	$ (5)	$ 129