INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Total unrecognized tax benefits at January 1	$ 1,013	$ 1,092	$ 1,235
Net amount of increases for current year’s tax positions	40	43	34
Gross amount of increases for prior years’ tax positions	46	324	273
Gross amount of decreases for prior years’ tax positions	(174)	(246)	(225)
Amounts of decreases relating to settlements	(283)	(199)	(174)
Reductions due to lapse of statutes of limitation	(23)	(11)	(21)
Foreign exchange, acquisitions and dispositions	(12)	10	(30)
Total unrecognized tax benefits at December 31	607	1,013	1,092
Amount of unrecognized tax benefit which would impact effective tax rate if recognized	$ 400	$ 800	$ 800