INVESTMENTS - Carrying Value of Non-marketable Equity Securities Measured Using the Measurement Alternative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Equity Securities without Readily Determinable Fair Value, Annual Amount [Abstract]
Measurement alternative—carrying value	$ 630,000,000		$ 538,000,000
Measurement alternative—impairment losses	5,000,000	$ 1,000,000
Measurement alternative—downward changes for observable prices	0	2,000,000
Measurement alternative—upward changes for observable prices	66,000,000	$ 123,000,000
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount [Abstract]
Measurement alternative—impairment losses	12,000,000
Measurement alternative—downward changes for observable prices	18,000,000
Measurement alternative—upward changes for observable prices	285,000,000
Non-marketable equity securities, impairment loss recognized in earnings	$ 0