CHANGE IN OPERATING WORKING CAPITAL - Components (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CHANGE IN OPERATING WORKING CAPITAL
Change in accounts receivable and other		$ 7
Change in other current assets	$ (3)	1
Change in accounts payable and accrued liabilities		(3)
Change in accounts payable to affiliates		(1)
Change in accrued interest	9	3
Change in operating working capital	$ 6	$ 7	[1]

[1] Recast to consolidate PNGTS (Refer to Note 2).