VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]
ASSETS (LIABILITIES)
Cash and cash equivalents	$ 68	$ 33	$ 77		$ 64
Accounts receivable and other	36	42
Contract assets	7
Inventories	7	8
Other current assets	11	7
Equity investments	1,217	1,213
Plant, property and equipment, net	2,105	2,123
Other assets	9	3
Accounts payable and accrued liabilities	(35)	(31)
Accounts payable to affiliates, net	(6)	(5)
Distributions payable	(2)	(1)
Accrued interest	(21)	(12)
Current portion of long-term debt	(45)	(51)
Long-term debt	(2,332)	(2,352)
Other liabilities	(29)	(29)
Consolidated VIEs | Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents	31	19
Accounts receivable and other	23	30
Contract assets	7
Inventories	6	6
Other current assets	6	5
Equity investments	1,217	1,213
Plant, property and equipment, net	1,126	1,133
Other assets	1	1
Accounts payable and accrued liabilities	(26)	(24)
Accounts payable to affiliates, net	(29)	(42)
Distributions payable	(2)	(1)
State taxes payable	(1)
Accrued interest	(5)	(2)
Current portion of long-term debt	(45)	(51)
Long-term debt	(308)	(308)
Other liabilities	(27)	(26)
Deferred state income tax	$ (10)	$ (10)

[1] Recast to consolidate PNGTS (Refer to Note 2).