INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized tax benefits	$ 5,130	$ 5,449
Portion that, if recognized, would reduce tax expense and effective tax rate	3,745	3,626
Accrued interest on unrecognized tax benefits	860	810
Accrued penalties on unrecognized tax benefits	188	158
Lower limit
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
Upper limit
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	1,200	900
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months	$ 1,300	$ 1,100