CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Cash Generated from Operations
Net income (loss)	[1]	$ (165)	$ 263		$ 263
Depreciation		97	97		96	[1]
Impairment of long lived assets (Note 7)		537
Impairment of goodwill (Note 4)		59
Amortization of debt issue costs reported as interest expense (Note 13)		2	2		2	[1]
Amortization of realized loss on derivative instrument (Note 20)		1	1		1	[1]
Equity earnings from equity investments (Note 5)		(173)	(124)		(97)	[1]
Distributions received from operating activities of equity investments (Note 5)		188	140		153	[1]
Change in other long term liabilities		(2)
Equity allowance for funds used during construction		(1)	(1)
Change in operating working capital (Note 16)		(3)	(2)		(1)	[1]
Cash generated from operations		540	376		417	[1]
Investing Activities
Distribution received from Iroquois as return of investment (Note 5)		10	5		0
Capital expenditures		(40)	(29)		(29)	[1]
Other		4	1		1	[1]
Investing activities		(35)	(761)		(230)	[1]
Financing Activities
Distributions paid (Note 15)		(218)	(284)		(250)	[1]
Distributions paid to non-controlling interests		(14)	(5)		(12)	[1]
Distributions paid to former parent of PNGTS			(1)		(9)	[1]
Common unit issuance, net (Note 11)		40	176		84	[1]
Common unit issuance subject to rescission, net (Note 11)	[1]				83
Long-term debt issued, net of discount (Note 9)		219	802		209	[1]
Long-term debt repaid (Note 9)		(516)	(310)		(270)	[1]
Debt issuance costs		(1)	(2)		(1)	[1]
Financing activities		(505)	354		(178)	[1]
Increase/(decrease) in cash and cash equivalents			(31)		9	[1]
Cash and cash equivalents, beginning of year		33	64	[1]	55	[1]
Cash and cash equivalents, end of year		33	33		64	[1]
Interest payments paid		94	79		66	[1]
State income taxes paid		1	2		2	[1]
Supplemental information about non-cash investing and financing activities
Accrued capital expenditures		7	9
Class B Units
Financing Activities
Distributions paid to Class B units (Notes 11 and 15)		(15)	(22)		(12)	[1]
Northern Border
Cash Generated from Operations
Equity earnings from equity investments (Note 5)		(68)	(67)		(69)
Investing Activities
Investment/Acquisition of interests			(83)
Great Lakes
Cash Generated from Operations
Equity earnings from equity investments (Note 5)		(59)	(31)		(28)
Investing Activities
Investment/Acquisition of interests		$ (9)	(9)		(9)	[1]
PNGTS
Investing Activities
Investment/Acquisition of interests	[1]				$ (193)
Portland Natural Gas Transmission System And Iroquois Acquisition
Investing Activities
Investment/Acquisition of interests			$ (646)

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