FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) Years	Dec. 31, 2019 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 12,663		$ 10,751
Level 3 | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	250		250
Long-term Investments | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	250		250
Long-term Investments | Level 3 | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	250		250
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	401		$ 501
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
Grab | Long-term Investments | Level 3 | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 200
Trip.com Group 1.25% Notes due 2022 | Long-term Investments | 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				$ 25
Weighted Average Cost of Capital | Didi Chuxing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		12.00%
Weighted Average Cost of Capital | Didi Chuxing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		14.00%
EBITDA Multiple | Didi Chuxing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number)		13
EBITDA Multiple | Didi Chuxing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number)		15
Volatility | Didi Chuxing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		60.00%
Volatility | Didi Chuxing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (percentages)		70.00%
Expected Term | Didi Chuxing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, inputs (number) | Years		4