EMPLOYEE BENEFIT PLANS (Components of Regulatory Assets and Accumulated Other Comprehensive Loss Not Recognized as Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Pension And Other Employee Benefit Plans [Line Items]
Net Loss	$ 129	$ 128
Prior Service Cost (Benefit)	1	0
Other Postretirement Benefits
Pension And Other Employee Benefit Plans [Line Items]
Net Loss	5	6
Prior Service Cost (Benefit)	$ (1)	$ (1)