INCOME TAXES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
State income taxes
Total state income taxes	$ 1	$ 1	$ 1	[1]
PNGTS
Income Taxes
Effective income tax rate (as a percent)	3.50%	3.80%	3.80%
State income taxes
Current	$ 2	$ 1	$ 1
Deferred	(1)
Total state income taxes	$ 1	$ 1	$ 1

[1] Recast to consolidate PNGTS (Refer to Notes 2 and 8).