INVESTMENTS - Carrying Value of Non-marketable Equity Securities Measured Using the Measurement Alternative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Equity Securities without Readily Determinable Fair Value, Annual Amount [Abstract]
Measurement alternative—carrying value	$ 1,079		$ 962
Measurement alternative—impairment losses	0	$ 3
Measurement alternative—downward changes for observable prices	0	0
Measurement alternative—upward changes for observable prices	81	25
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount [Abstract]
Measurement alternative—impairment losses	68
Measurement alternative—downward changes for observable prices	53
Measurement alternative—upward changes for observable prices	567
Non-marketable equity securities, impairment loss recognized in earnings	$ 0	$ 0