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Amount of cash outflow to settle contingent consideration liability.

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Shares restricted for trading purposes until the required post-acquisition services are completed by certain employees

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Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount of liability recognized arising from contingent consideration in a business combination.

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Amount of assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount of liabilities assumed at the acquisition date.

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Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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The cash inflow associated with the acquisition of business during the period (for example, cash that was held by the acquired business).

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The cash outflow associated with the acquisition of a controlling interest in another entity or an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, joint venture or equity method investment).

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Value of stock issued pursuant to acquisitions during the period.

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ACQUISITIONS (Details) - USD ($) $ in Millions				12 Months Ended
ACQUISITIONS (Details) - USD ($) $ in Millions	Nov. 30, 2018	Apr. 26, 2018	Jul. 24, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired				$ 9	$ 273	$ 553
Stock Issued During Period, Value, Acquisitions					110
Non-cash investing and financing activity for an acquisition				0	59	0
Goodwill				2,913	2,910	2,738
Deferred tax liability established as a result of identifiable intangible assets acquired				133	482
Acquisition related costs						$ 5
Payment for Contingent Consideration Liability, Total				$ 37
FareHarbor [Member]
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired		$ 139
Restricted Stock, Issued		51
HotelsCombined [Member]
Business Acquisition [Line Items]
Acquisitions and other investments, net of cash acquired	$ 134
Momondo Group
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 556
Current assets			50
Identifiable intangible assets			333
Goodwill			288
Property and equipment			1
Total liabilities			(116)
Purchase price, total consideration			556
Cash Acquired from Acquisition			15
Deferred tax liability established as a result of identifiable intangible assets acquired			70
Debt assumed in acquisition(s)			15
Supply and distribution agreements \| Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 214
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			15 years
Trade names \| Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 104
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			13 years
Technology \| Momondo Group
Business Acquisition [Line Items]
Identifiable intangible assets			$ 15
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			4 years
Additional Paid-in Capital
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions					110
Additional Paid-in Capital \| FareHarbor [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions		$ 110
Level 3 \| Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability					$ 28