INVESTMENTS - Carrying Value of Non-marketable Equity Securities Measured Using the Measurement Alternative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Equity Securities without Readily Determinable Fair Value, Annual Amount [Abstract]
Measurement alternative—carrying value	$ 688,000,000		$ 688,000,000		$ 538,000,000
Measurement alternative—impairment losses	1,000,000	$ 0	9,000,000	$ 4,000,000
Measurement alternative—downward changes for observable prices	4,000,000	14,000,000	16,000,000	18,000,000
Measurement alternative—upward changes for observable prices	23,000,000	21,000,000	108,000,000	133,000,000
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount [Abstract]
Measurement alternative—impairment losses	16,000,000		16,000,000
Measurement alternative—downward changes for observable prices	34,000,000		34,000,000
Measurement alternative—upward changes for observable prices	327,000,000		327,000,000
Non-marketable equity securities, impairment loss recognized in earnings	$ 0	$ 0	$ 0	$ 0