INCOME TAXES (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Dec. 31, 2016
State income taxes
Total state income taxes	$ 1	$ 1	[1]
Portland Natural Gas Transmission System
Income Taxes
Effective income tax rate (as a percent)	3.80%			3.80%
State income taxes
Current	$ 1	8
Deferred		(7)
Total state income taxes	$ 1	$ 1

[1] Recast to consolidate PNGTS for all periods presented (Refer to Notes 2 and 6).