INCOME TAXES - Gross Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1	$ 1,001	$ 913	$ 735
Increases and decreases as a result of positions taken during prior years
Transfers from valuation allowances	0	15	2
Other increases, including currency translation	10	22	164
Other decreases, including currency translation	(10)	(10)	(35)
Increases related to acquired businesses	7	0	0
Increases as a result of positions taken during the current year	58	80	69
Decreases relating to settlements with tax authorities	(26)	(16)	(3)
Decreases as a result of a lapse of the applicable statute of limitations	(4)	(3)	(19)
Balance at December 31	$ 1,036	$ 1,001	$ 913