EMPLOYEE BENEFIT PLANS (Pension and Other Postretirement Benefit Amounts included in Consolidated Balance Sheet ) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Pension And Other Employee Benefit Plans [Line Items]
Regulatory Assets	$ 388	$ 281
Pension Benefits
Pension And Other Employee Benefit Plans [Line Items]
Regulatory Assets	121	123
Accrued Employee Expenses	(1)	(1)
Pension and Other Postretirement Benefits	(71)	(69)
Accumulated Other Comprehensive Loss, SERP	9	6
Net Amount Recognized	58	59
Other Postretirement Benefits
Pension And Other Employee Benefit Plans [Line Items]
Regulatory Assets	5	5
Accrued Employee Expenses	(2)	(2)
Pension and Other Postretirement Benefits	(63)	(63)
Accumulated Other Comprehensive Loss, SERP	0	0
Net Amount Recognized	$ (60)	$ (60)