VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2017	Dec. 31, 2016		Sep. 30, 2016	[1]	Dec. 31, 2015	[1]
ASSETS (LIABILITIES)
Cash and cash equivalents		$ 73	$ 64	[1]	$ 77		$ 55
Accounts receivable and other		35	47	[1]
Inventories		7	7	[1]
Other current assets		6	7	[1]
Equity investments		1,207	918	[1]
Plant, property and equipment		2,133	2,180	[1]
Other assets	[1]		1
Accounts payable and accrued liabilities		(31)	(29)	[1]
Accounts payable to affiliates, net		(5)	(8)	[1]
Distributions payable	[1]		(3)
Accrued interest		(21)	(10)	[1]
Current portion of long-term debt		(51)	(52)	[1]
Long-term debt		(2,427)	(1,859)	[1]
Other liabilities		(28)	(28)	[1]
Consolidated VIEs | Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents		19	14
Accounts receivable and other		23	33
Inventories		6	6
Other current assets		4	6
Equity investments		1,207	918
Plant, property and equipment		1,132	1,146
Other assets		1	2
Accounts payable and accrued liabilities		(21)	(21)
Accounts payable to affiliates, net		(25)	(32)
Distributions payable			(3)
Other taxes payable		(1)
Accrued interest		(5)	(2)
Current portion of long-term debt		(51)	(52)
Long-term debt		(314)	(337)
Other liabilities		(26)	(25)
Deferred state income tax		$ (10)	$ (10)

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