VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016		Jun. 30, 2016		Dec. 31, 2015	[1]
ASSETS (LIABILITIES)
Cash and cash equivalents		$ 51	$ 64	[1]	$ 52	[1]	$ 55
Accounts receivable and other		37	47	[1]
Inventories		7	7	[1]
Other current assets		5	7	[1]
Equity investments		1,138	918	[1]	$ 918
Plant, property and equipment		2,148	2,180	[1]
Other assets	[1]		1
Accounts payable and accrued liabilities		(27)	(29)	[1]
Accounts payable to affiliates, net		(35)	(8)	[1]
Distributions payable	[1]		(3)
Accrued interest		(11)	(10)	[1]
Current portion of long-term debt		(57)	(52)	[1]
Long-term debt		(2,333)	(1,859)	[1]
Other liabilities		(28)	(28)	[1]
Consolidated VIEs | Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents		13	14
Accounts receivable and other		26	33
Inventories		6	6
Other current assets		3	6
Equity investments		1,138	918
Plant, property and equipment		1,137	1,146
Other assets		1	2
Accounts payable and accrued liabilities		(20)	(21)
Accounts payable to affiliates, net		(39)	(32)
Distributions payable			(3)
Accrued interest		(1)	(2)
Current portion of long-term debt		(57)	(52)
Long-term debt		(304)	(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).