REGULATORY MATTERS Net Changes in Regulatory Assets and Liabilities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Revenue Accruals and Deferrals
Beginning balance	$ (1)
Net collection of 2015 revenue deferrals and accruals, including accrued interest	(11)
Net revenue accrual	(47)
Net accrued interest payable	(2)
Ending balance	$ (61)