CHANGES IN ACCUMULATED OTHER COMPREHENSIVE LOSS BY COMPONENT (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021		Jun. 30, 2020	May 31, 2020
Total AOCI, net of tax
Balance		$ 4,764	$ 3,831	$ 4,893		$ 5,933
OCI, before reclassifications, net of tax		106	94	64		(60)
Amounts reclassified to net income, net of tax	[1]	11	15	11		18
Total other comprehensive income (loss), net of tax		117	109	75		(42)
Balance		4,799	3,999	4,799		3,999
Trip.com Group Note Due 2020 | Convertible Debt Securities
Total AOCI, net of tax
Amortized cost of available-for-sale debt securities							$ 250
Total AOCI
Total AOCI, net of tax
Balance		(160)	(342)	(118)		(191)
Balance		(43)	(233)	(43)		(233)
Foreign currency translation adjustments
Total AOCI, net of tax
Balance		(119)	(216)	(89)		(139)
OCI, before reclassifications, net of tax		8	32	(22)		(45)
Amounts reclassified to net income, net of tax	[1]	0	0	0	[2]	0
Total other comprehensive income (loss), net of tax		8	32	(22)		(45)
Balance		(111)	(184)	(111)		(184)
Foreign currency translation adjustments | Net Investment Hedging | Foreign Currency Forward
Before tax
Balance		(53)	(53)	(53)		(53)
Balance		(53)	(53)	(53)		(53)
Total AOCI, net of tax
Balance		(35)	(35)	(35)		(35)
Balance		(35)	(35)	(35)		(35)
Foreign currency translation
Before tax
Balance		(106)	(314)	11		(186)
OCI before reclassifications, before tax		24	65	(93)		(63)
Amounts reclassified to net income, before tax	[1]	0	0	0		0
OCI after reclassifications, before tax		24	65	(93)		(63)
Balance		(82)	(249)	(82)		(249)
Tax (expense) benefit
Balance	[3]	51	58	47		54
OCI before reclassifications, tax	[3]	(1)	0	3		4
Amounts reclassified to net income, tax	[1],[3]	0	0	0		0
OCI after reclassifications, tax	[3]	(1)	0	3		4
Balance	[3]	50	58	50		58
Net Investment Hedges
Before tax
Balance	[2]	(75)	60	(184)		(2)
OCI before reclassifications, before tax	[2]	(20)	(43)	89		19
Amounts reclassified to net income, before tax	[1],[2]	0	0	0		0
OCI after reclassifications, before tax	[2]	(20)	(43)	89		19
Balance	[2]	(95)	17	(95)		17
Tax (expense) benefit
Balance	[2]	11	(20)	37		(5)
OCI before reclassifications, tax	[2]	5	10	(21)		(5)
Amounts reclassified to net income, tax	[1],[2]	0	0	0		0
OCI after reclassifications, tax	[2]	5	10	(21)		(5)
Balance	[2]	16	(10)	16		(10)
Unrealized losses on cash flow hedges
Before tax
Balance	[4]	(15)	0	0		0
OCI before reclassifications, before tax	[4]	0	0	(15)		0
Amounts reclassified to net income, before tax	[1],[4]	15	0	15		0
OCI after reclassifications, before tax	[4]	15	0	0		0
Balance	[4]	0	0	0		0
Tax (expense) benefit
Balance	[4]	4	0	0		0
OCI before reclassifications, tax	[4]	0	0	4		0
Amounts reclassified to net income, tax	[1],[4]	(4)	0	(4)		0
OCI after reclassifications, tax	[4]	(4)	0	0		0
Balance	[4]	0	0	0		0
Total AOCI, net of tax
Balance	[4]	(11)	0	0		0
OCI, before reclassifications, net of tax	[4]	0	0	(11)		0
Amounts reclassified to net income, net of tax	[1],[4]	11	0	11		0
Total other comprehensive income (loss), net of tax	[4]	11	0	0		0
Balance	[4]	0	0	0		0
Net unrealized gains (losses) on available-for-sale securities
Before tax
Balance		2	(97)	3		(7)
OCI before reclassifications, before tax		128	73	127		(21)
Amounts reclassified to net income, before tax	[1]	0	0	0		4
OCI after reclassifications, before tax		128	73	127		(17)
Balance		130	(24)	130		(24)
Tax (expense) benefit
Balance		(32)	(29)	(32)		(45)
OCI before reclassifications, tax		(30)	(11)	(30)		6
Amounts reclassified to net income, tax	[1]	0	15	0		14
OCI after reclassifications, tax		(30)	4	(30)		20
Balance		(62)	(25)	(62)		(25)
Total AOCI, net of tax
Balance		(30)	(126)	(29)		(52)
OCI, before reclassifications, net of tax		98	62	97		(15)
Amounts reclassified to net income, net of tax	[1]	0	15	0		18
Total other comprehensive income (loss), net of tax		98	77	97		3
Balance		$ 68	(49)	$ 68		(49)
Net unrealized gains (losses) on available-for-sale securities | Trip.com Group Note Due 2020 | Convertible Debt Securities
Tax (expense) benefit
Amounts reclassified to net income, tax			$ 15			$ 15

[1]    The reclassified losses before tax are included in "Other income (expense), net" and the related reclassified tax benefits are included in "Income tax expense (benefit)" in the Unaudited Consolidated Statements of Operations. The cost of marketable debt securities sold is determined using a first-in and first-out method. For the three and six months ended June 30, 2020, the amounts reclassified to net income include a tax expense of $15 million related to the maturity in May 2020 of the Company's investment of $250 million in Trip.com Group convertible notes. The tax expense is included in "Income tax expense (benefit)" in the Unaudited Consolidated Statements of Operations.

[2] Net investment hedges balance at June 30, 2021 and earlier dates presented above, includes 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 of the foreign currency exposure of the net investment in certain Euro functional currency subsidiaries (see Note 9).

[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").

[4] Relates to the reverse treasury lock agreements entered in March 2021 that were designated as cash flow hedges and settled in April 2021 (see Note 6).