INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized tax benefits	$ 4,191	$ 4,169	$ 5,563	$ 5,449
Portion that, if recognized, would reduce tax expense and effective tax rate	2,986	2,701	4,265
Accrued interest on unrecognized tax benefits	628	722	934
Accrued penalties on unrecognized tax benefits	179	195	182
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	0
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months	0	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	250	650	1,200
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months	$ 350	$ 700	$ 1,300