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INVESTMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
INVESTMENTS (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jul. 17, 2018	Oct. 31, 2017	Sep. 12, 2016	Aug. 07, 2014
Schedule of Investments [Line Items]
Net unrealized (losses) gains on marketable equity securities	$ (49)	$ 31	$ 419	$ 107
Marketable securities:
Short-term investments in marketable securities	973		$ 973		$ 3,660
Investments [Abstract]
Weighted average life of all fixed income investments, excluding the Company's investment in Ctrip convertible debt securities			1 year 2 months 12 days
Investment in equity securities without readily determinable FV	501		$ 501		501
Trip.com Group
Schedule of Investments [Line Items]
Net unrealized (losses) gains on marketable equity securities	(165)	(226)	48	(150)
Meituan-Dianping
Schedule of Investments [Line Items]
Net unrealized (losses) gains on marketable equity securities	116	$ 257	371	$ 257
Investments in Equity securities:
Cost Method Investments							$ 450
Fair Value	822		822		451
Didi Chuxing
Investments [Abstract]
Investment in equity securities without readily determinable FV						$ 500
Trip.com Group convertible debt securities \| Trip.com Group
Debt securities:
Cost	775		775
Short-term Investments
Marketable securities:
Cost	975		975		3,674
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(2)		(2)		(14)
Short-term investments in marketable securities	973		973		3,660
Short-term Investments \| International government securities
Debt securities:
Cost	108		108		314
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	108		108		314
Short-term Investments \| U.S. government securities
Debt securities:
Cost	154		154		658
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(1)		(1)		(2)
Fair Value	153		153		656
Short-term Investments \| Corporate debt securities
Debt securities:
Cost	704		704		2,693
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(1)		(1)		(12)
Fair Value	703		703		2,681
Short-term Investments \| U.S. government agency securities
Debt securities:
Cost					1
Gross Unrealized Gains					0
Gross Unrealized Losses					0
Fair Value					1
Short-term Investments \| Commercial paper
Debt securities:
Cost					7
Gross Unrealized Gains					0
Gross Unrealized Losses					0
Fair Value					7
Short-term Investments \| Time deposits and certificates of deposit
Debt securities:
Cost	9		9		1
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	9		9		1
Short-term Investments \| Trip.com Group convertible debt securities \| Trip.com Group 1% Notes due 2019
Debt securities:
Cost									$ 500
Long-term Investments
Investments in Equity securities:
Cost	1,105		1,105		1,105
Gross Unrealized Gains	389		389		3
Gross Unrealized Losses	(39)		(39)		(72)
Fair Value	1,455		1,455		1,036
Marketable securities:
Cost	3,252		3,252		7,921
Gross Unrealized Gains	392		392		10
Gross Unrealized Losses	(76)		(76)		(224)
Long-term investments	3,568		3,568		7,707
Long-term Investments \| Trip.com Group
Investments in Equity securities:
Cost	655		655		655
Fair Value	633		633		585
Long-term Investments \| International government securities
Debt securities:
Cost	28		28		797
Gross Unrealized Gains	0		0		3
Gross Unrealized Losses	0		0		0
Fair Value	28		28		800
Long-term Investments \| U.S. government securities
Debt securities:
Cost	178		178		299
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		(6)
Fair Value	178		178		293
Long-term Investments \| Corporate debt securities
Debt securities:
Cost	1,166		1,166		4,445
Gross Unrealized Gains	3		3		4
Gross Unrealized Losses	(3)		(3)		(48)
Fair Value	1,166		1,166		4,401
Long-term Investments \| Trip.com Group convertible debt securities \| Trip.com Group
Debt securities:
Cost	775		775		1,275
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(34)		(34)		(98)
Fair Value	741		741		1,177
Long-term Investments \| Trip.com Group convertible debt securities \| Trip.com Group 1% Note due 2020
Debt securities:
Cost	250		250
Long-term Investments \| Trip.com Group convertible debt securities \| Trip.com Group 1.25% Notes due 2022
Debt securities:
Cost								$ 25
Other Long-term Investments \| Redeemable Convertible Preferred Stock [Member]
Debt securities:
Cost	$ 250		$ 250		$ 200