ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 31, 2019	Jan. 01, 2018	Jan. 01, 2017	Dec. 31, 2016
Total, net of tax
Balance		$ 8,785	$ 11,261	$ 9,820
OCI before reclassifications		114		374
Amounts reclassified to net income	[1]	11		(1)
Total other comprehensive income (loss), net of tax		125	(313)	373
Amounts reclassified to retained earnings						$ 189	$ 280
Balance		5,933	8,785	11,261
International Investments
Total, net of tax
Deferred tax expense related to net cumulative unrealized gains associated with international investments				63
Debt Securities | Trip.com Group 1% Notes due 2019 | Short-term Investments
Total, net of tax
Tax expense related to the maturity of investments		21
Investment in convertible notes					$ 500
Foreign Exchange Forward | Net Investment Hedging | Designated as Hedging Instrument
Total, net of tax
Accumulated net losses from fair value adjustments, net of tax		(35)	(35)	(35)				$ (35)
Accumulated net losses from fair value adjustments, before tax		(53)	(53)	(53)				$ (53)
ASU 2016-01
Total, net of tax
Amounts reclassified to retained earnings	[2]					(241)
Foreign Currency Translation Adjustments
Total, net of tax
Balance		(129)	(15)	(312)
OCI before reclassifications		(10)	(114)	297
Amounts reclassified to net income	[1]	0		0
Total other comprehensive income (loss), net of tax		(10)	(114)	297
Balance		(139)	(129)	(15)
Foreign Currency Translation Adjustments - Net Investment Hedges
Before tax
Balance	[2]	(73)	(290)	258
OCI before reclassifications	[2]	71	217	(548)
Amounts reclassified to net income	[1],[2]	0		0
OCI for the period	[2]	71	217	(548)
Balance	[2]	(2)	(73)	(290)
Tax (expense) benefit
Balance	[2]	12	65	(110)
OCI before reclassifications	[2]	(17)	(53)	175
Amounts reclassified to net income	[1],[2]	0		0
OCI for the period	[2]	(17)	(53)	175
Balance	[2]	(5)	12	65
Foreign Currency Translation Adjustments - Foreign Currency Translation
Before tax
Balance		(109)	210	(460)
OCI before reclassifications		(77)	(319)	670
Amounts reclassified to net income	[1]	0		0
OCI for the period		(77)	(319)	670
Balance		(186)	(109)	210
Tax (expense) benefit
Balance	[3]	41	0	0
OCI before reclassifications	[3]	13	41	0
Amounts reclassified to net income	[1],[3]	0		0
OCI for the period	[3]	13	41	0
Balance	[3]	54	41	0
Net Unrealized Gains (Losses) on Available-For-Sale Securities
Before tax
Balance	[4]	(157)	343	186
OCI before reclassifications	[4]	161	(201)	158
Amounts reclassified to net income	[1],[4]	(11)		(1)
OCI for the period	[4]	150	(201)	157
Balance	[4]	(7)	(157)	343
Tax (expense) benefit
Balance	[4],[5]	(30)	(90)	(9)
OCI before reclassifications	[4],[5]	(37)	2	(81)
Amounts reclassified to net income	[1],[4],[5]	22		0
OCI for the period	[4],[5]	(15)	2	(81)
Balance	[4],[5]	(45)	(30)	(90)
Total, net of tax
Balance	[4]	(187)	253	177
OCI before reclassifications	[4]	124	(199)	77
Amounts reclassified to net income	[1],[4]	11		(1)
Total other comprehensive income (loss), net of tax	[4]	135	(199)	76
Balance	[4]	(52)	(187)	253
Net Unrealized Gains (Losses) on Available-For-Sale Securities | ASU 2016-01
Before tax
Amounts reclassified to retained earnings	[2],[4]					(299)
Tax (expense) benefit
Amounts reclassified to retained earnings	[2],[4],[5]					58
Total, net of tax
Amounts reclassified to retained earnings	[2],[4]					(241)
AOCI
Total, net of tax
Balance		(316)	238	(135)
OCI before reclassifications			(313)
Amounts reclassified to retained earnings						$ (241)
Balance		$ (191)	$ (316)	$ 238

[1] (5)         The reclassified net gains on available-for-sale securities, before tax, are included in "Foreign currency transactions and other" and the reclassified tax expenses are included in "Income tax expense" in the Consolidated Statements of Operations. For the year ended December 31, 2019, the reclassified tax expenses includes a tax expense of $21 million related to the maturity in August 2019 of the Company's investment of $500 million in Trip.com Group convertible notes (see Note 5).

[2] (2)         Net investment hedges balance, net of tax, at December 31, 2016, 2017, 2018 and 2019 include accumulated net losses from fair value adjustments of $35 million ($53 million before tax) associated with previously settled derivatives that were designated as net investment hedges. The remaining balances relate to foreign currency transaction gains (losses) and related tax benefits (expenses) associated with the Company's Euro-denominated debt that is designated as a hedge against the impact of currency fluctuations on the net assets of a Euro functional currency subsidiary (see Notes 2 and 12).

[3] (3)         The tax benefits relate to foreign currency translation adjustments to the Company's one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the enactment of the U.S. Tax Cuts and Jobs Act (the "Tax Act"). Prior to January 1, 2018, foreign currency translation adjustments were not subject to U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States.

[4] (1)         Upon the adoption of the accounting update on financial instruments on January 1, 2018, the Company reclassified net unrealized gains, net of tax, of $241 million ($299 million before tax) related to marketable equity securities from AOCI to retained earnings. Changes in fair value of marketable equity securities subsequent to January 1, 2018 are recognized in net income rather than "Accumulated other comprehensive loss" in the Consolidated Balance Sheets (see Note 2).

[5] (4)         The tax expense for the year ended December 31, 2017 includes a U.S. deferred tax expense of $63 million related to net cumulative unrealized gains associated with certain international investments.