FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 09, 2018	Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Restricted cash	$ 2	$ 77	$ 77	$ 0
Letter of credit		$ 77
Recurring basis
Assets:
Cash equivalents	197		265
Restricted cash	2		77
Liabilities:
Acquisition-related contingent consideration	339		387
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	166		230
Restricted cash	2		77
Liabilities:
Acquisition-related contingent consideration	0		0
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	31		35
Restricted cash	0		0
Liabilities:
Acquisition-related contingent consideration	0		0
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0		0
Restricted cash	0		0
Liabilities:
Acquisition-related contingent consideration	$ 339		$ 387