INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized tax benefits	$ 5,449	$ 4,692	$ 6,778
Portion that, if recognized, would reduce tax expense and effective tax rate	3,626	2,886
Accrued interest on unrecognized tax benefits	810	615
Accrued penalties on unrecognized tax benefits	158	118
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	0	0
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months	0	0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	900	500
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months	$ 1,100	$ 600