TRANSACTIONS WITH MAJOR CUSTOMERS (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Transactions with major customers
Revenues	$ 109	$ 100	$ 101	$ 112	$ 111	$ 103	$ 101	$ 111	$ 422	$ 426	[1],[2]	$ 417	[1]
Trade accounts receivable	40				44				40	44
Total revenues | Customer concentration risk | Anadarko Energy Services Company
Transactions with major customers
Revenues									48	48		48
Total revenues | Customer concentration risk | Pacific Gas and Electric Company
Transactions with major customers
Revenues									33	36		$ 42
Accounts receivable and other | Amounts owed by major customers | Anadarko Energy Services Company
Transactions with major customers
Trade accounts receivable	$ 4				$ 4				$ 4	$ 4

[1] Recast to consolidate PNGTS (Refer to Notes 2 and 7).

[2] Recast to consolidate PNGTS (Refer to Notes 2 and 7).