ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of year		$ 963
Change in fair value of interest rate derivative instruments recognized in other comprehensive income		(2)	$ 5	$ 3	[1]
PNGTS' amortization of realized loss on derivative instrument (Note 20)		1	1	1	[1]
Net other comprehensive income	[1]	3	7	3
Partners' Equity at end of year		591	963
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of year		5	(2)	(4)
Change in fair value of interest rate derivative instruments recognized in other comprehensive income		(2)	5	3
Amounts reclassified from AOCI		5		(2)
PNGTS' amortization of realized loss on derivative instrument (Note 20)		1	1	1
Other comprehensive income (loss) - effects of Iroquois' retirement benefit plans		(1)	1
Net other comprehensive income		3	7	2
Partners' Equity at end of year		8	5	(2)
Cash flow hedges
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of year		4	(2)	(4)
Change in fair value of interest rate derivative instruments recognized in other comprehensive income		(2)	5	3
Amounts reclassified from AOCI		5		(2)
PNGTS' amortization of realized loss on derivative instrument (Note 20)		1	1	1
Net other comprehensive income		4	6	2
Partners' Equity at end of year		8	4	$ (2)
Equity Investments
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of year		1
Other comprehensive income (loss) - effects of Iroquois' retirement benefit plans		(1)	1
Net other comprehensive income		$ (1)	1
Partners' Equity at end of year			$ 1

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