Acquisitions and Other Investments - Summary of Fair Value of Assets Acquired and Liabilities Assumed in Conjunction with Acquisition (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Goodwill	$ 8,120	$ 8,229	$ 7,942
Travel Related Companies
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Goodwill	31	124
Intangible assets with definite lives	24	76
Net assets and non-controlling interests acquired		15
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Deferred tax liabilities	(1)	(21)
Total	$ 54	$ 194

Amount of assets acquired at the acquisition date.

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Amount of deferred tax liability attributable to taxable temporary differences assumed 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 recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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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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