INCOME TAXES - Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Uncertain Tax Positions
Balance at the beginning of the period	$ 46	$ 43
Total balance at beginning of the period	55	53
Current year tax positions: Additions	13	11
Current year tax positions: Reductions	0	(1)
Prior year tax positions: Additions	3	1
Prior year tax positions: Reductions	(1)	(2)
Lapse of applicable statute of limitations	(7)	(6)
Balance at the end of the period	54	46
Total balance at the end of the period	62	55
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense [Abstract]
Interest and penalties at period start	9	10
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(1)	(1)
Interest and penalties at period end	$ 8	$ 9