FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jan. 09, 2018	Dec. 31, 2017	Sep. 30, 2017
Liabilities:
Highly liquid investments, maturity period (in months)	3 months
Restricted cash	$ 0	$ 77	$ 77	$ 928
Letters of credit		$ 77
Recurring basis
Assets:
Cash equivalents	251		265
Restricted cash	0		77
Liabilities:
Acquisition-related contingent consideration	(336)		(387)
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	227		230
Restricted cash	0		77
Liabilities:
Acquisition-related contingent consideration	0		0
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	24		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	$ (336)		$ (387)