REGULATORY MATTERS (Purchased Power Fuel Adjustment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Regulatory Asset (Liability) [Roll Forward]
Beginning of Period	$ (605)
End of Period	(607)	$ (605)
Purchased Power and Fuel Adjustment Clause
Regulatory Asset (Liability) [Roll Forward]
Beginning of Period	(9)	(38)
Deferred Fuel and Purchased Power Costs	2	14
PPFAC Refunds (Recoveries)	(10)	15
End of Period	$ (17)	$ (9)