INVESTMENTS - Carrying Value of Non-marketable Equity Securities Measured Using the Measurement Alternative (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Measurement alternative—balance as of September 30, 2018	$ 452,000,000	$ 452,000,000
Measurement alternative—impairment losses	0	4,000,000
Measurement alternative—downward changes for observable prices	14,000,000	18,000,000
Measurement alternative—upward changes for observable prices	21,000,000	133,000,000
Non-marketable equity securities, impairment loss recognized in earnings	$ 0	$ 0