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FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 14,859		$ 14,054
Level 3 | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	330		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	$ 69		455
Grab | Redeemable Convertible Preferred Stock | Relative Weighting | Market Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.70
Grab | Redeemable Convertible Preferred Stock | Relative Weighting | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.30
Grab | Redeemable Convertible Preferred Stock | Volatility | Market Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.65
Grab | Redeemable Convertible Preferred Stock | Expected Term | Market Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time to liquidity	3 months
Grab | Redeemable Convertible Preferred Stock | Expected Term | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time to liquidity	5 months
Grab | Redeemable Convertible Preferred Stock | Minimum | Volatility | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.60
Grab | Redeemable Convertible Preferred Stock | Minimum | Weighted average cost of capital | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.120
Grab | Redeemable Convertible Preferred Stock | Minimum | EBITDA Multiple | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	12
Grab | Redeemable Convertible Preferred Stock | Maximum | Volatility | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.70
Grab | Redeemable Convertible Preferred Stock | Maximum | Weighted average cost of capital | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	0.145
Grab | Redeemable Convertible Preferred Stock | Maximum | EBITDA Multiple | Income Approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement inputs	14
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	330		200
DiDi Global Inc. | 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 Senior Notes, Issued September 2016 | Short-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

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