Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of foreign currency derivatives not designated as hedging instruments.

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FAIR VALUE MEASUREMENTS - Effect of Foreign Currency Exchange Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Losses on foreign currency exchange derivatives	$ 0	$ 21	$ 31	$ 26
Trip.com Group 1.25% Notes due 2022 \| Trip.com Group convertible debt securities \| Long-term Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortized cost of available-for-sale debt securities					$ 25