INVESTMENTS - Carrying Value of Non-marketable Equity Securities Measured Using the Measurement Alternative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Measurement alternative, balance at June 30, 2018	$ 415,000,000	$ 415,000,000
Measurement alternative—impairment losses	3,000,000	4,000,000
Measurement alternative—downward changes for observable prices	2,000,000	4,000,000
Measurement alternative—upward changes for observable prices	4,000,000	112,000,000
Non-marketable equity securities, impairment loss recognized in earnings	$ 0	$ 0