VARIABLE INTEREST ENTITIES - Consolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
ASSETS (LIABILITIES)
Cash and cash equivalents	$ 51	$ 33	$ 51	$ 64
Accounts receivable and other	40	42
Inventories	8	8
Other current assets	9	7
Equity investments	1,211	1,213
Plant, property and equipment, net	2,086	2,123
Other assets	11	3
Accounts payable and accrued liabilities	(27)	(31)
Accounts payable to affiliates, net	(6)	(5)
Distributions payable		(1)
Accrued interest	(12)	(12)
Current portion of long-term debt	(36)	(51)
Long-term debt	(2,272)	(2,352)
Other liabilities	(28)	(29)
Consolidated VIEs | Restricted VIEs
ASSETS (LIABILITIES)
Cash and cash equivalents	7	19
Accounts receivable and other	27	30
Inventories	7	6
Other current assets	6	5
Equity investments	1,211	1,213
Plant, property and equipment, net	1,117	1,133
Other assets	2	1
Accounts payable and accrued liabilities	(18)	(24)
Accounts payable to affiliates, net	(44)	(42)
Distributions payable		(1)
Accrued interest	(3)	(2)
Current portion of long-term debt	(36)	(51)
Long-term debt	(273)	(308)
Other liabilities	(27)	(26)
Deferred state income tax	$ (10)	$ (10)