INCOME TAXES (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended			12 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	$ (7)	$ 1	1
Deferred	$ 7
Total state income taxes		$ 1	$ 1

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