FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Designated as Hedging Instrument | Cash Flow Hedging | Reverse Treasury Lock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount		$ 1,800
Unrealized loss on derivatives		15
Designated as Hedging Instrument | Cash Flow Hedging | Reverse Treasury Lock | Subsequent Event
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Settlement of reverse treasury lock agreements	$ 15
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value		15,657	$ 14,054
Level 3 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value		200	200
Long-term Investments | Investment in private company equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in equity securities without readily determinable FV		452	455
Grab | Long-term Investments | Redeemable Convertible Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost of available-for-sale debt securities		200	200
Grab | Long-term Investments | Redeemable Convertible Preferred Stock | Level 3 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value		200	200
Didi Chuxing | Long-term Investments | Investment in private company equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in equity securities without readily determinable FV		400	400	$ 400
Trip.com Group | Convertible Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost of available-for-sale debt securities		525
Trip.com Group | Long-term Investments | Convertible Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized cost of available-for-sale debt securities		25	25
Trip.com Group | Long-term Investments | Convertible Debt Securities | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value		24	24
Trip.com Group | Long-term Investments | Convertible Debt Securities | Level 3 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value		$ 0	$ 0