INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of the year	$ 42	$ 62	$ 72
Gross decrease for tax positions related to prior years	(27)	(19)	(6)
Gross increase for tax positions related to prior years	0	1	0
Decreases for tax positions as a result of the lapse of the statutes of limitations	(1)	(2)	(3)
Decreases for tax positions related to settlements with taxing authorities	(9)	0	(1)
Balance at end of year	$ 5	$ 42	$ 62