ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of period		$ 760	$ 699	$ 1,068
Change in fair value of cash flow hedges		(16)	(13)	(2)
Amounts reclassified from AOCI		7	(1)	5
PNGTS’ amortization of realized loss on derivative instrument (Note 19)		0	0	1
Other comprehensive income - effects of Iroquois’ retirement benefit plans		1	1	(1)
Net other comprehensive income		(8)	(13)	3
Partners' Equity at end of period		833	760	699
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of period	[1]	(5)	8	5
Net other comprehensive income	[1]	(8)	(13)	3
Partners' Equity at end of period	[1]	(13)	(5)	8
Cash flow hedges
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of period		(6)	8	4
Change in fair value of cash flow hedges		(16)	(13)	(2)
Amounts reclassified from AOCI		7	(1)	5
PNGTS’ amortization of realized loss on derivative instrument (Note 19)				1
Other comprehensive income - effects of Iroquois’ retirement benefit plans		0	0	0
Net other comprehensive income		(9)	(14)	4
Partners' Equity at end of period		(15)	(6)	8
Equity Investments
Changes in accumulated other comprehensive income (loss) (AOCI) by component
Partners' Equity at beginning of period		1	0	1
Change in fair value of cash flow hedges		0	0	0
Amounts reclassified from AOCI		0	0	0
PNGTS’ amortization of realized loss on derivative instrument (Note 19)				0
Other comprehensive income - effects of Iroquois’ retirement benefit plans		1	1	(1)
Net other comprehensive income		1	1	(1)
Partners' Equity at end of period		$ 2	$ 1	$ 0

[1] Gains / losses related to cash flow hedges reported in accumulated other comprehensive income (loss) (AOCI) and expected to be reclassified to net income in the next 12 months are estimated to be a loss of $9 million. This estimate assumes constant interest rates over time; however, the amounts reclassified will vary based on actual value of interest rates at the date of settlement.