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INVESTMENTS - Narrative (Details) $ in Millions		3 Months Ended				9 Months Ended		12 Months Ended
		Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Schedule of Investments [Line Items]
Proceeds from sale and maturity of investments						$ 8	$ 2,997
Impairment of investment	[1]		$ 0	$ 0		0	100
Government and corporate debt securities
Schedule of Investments [Line Items]
Proceeds from sales and maturities of investments							2,200
Trip.com Group
Schedule of Investments [Line Items]
Cost of investment in equity securities with readily determinable fair values				655			655
Proceeds from sale and maturity of investments							525
Net realized loss on securities							201
Trip.com Group | Convertible Debt Securities
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities			525			525
Meituan
Schedule of Investments [Line Items]
Payments to acquire other investments									$ 450
Unrealized (losses) gains on equity securities held			$ (772)	$ 727		$ (509)	$ 1,400
DiDi Global Inc.
Schedule of Investments [Line Items]
Payments to acquire other investments								$ 500
ADSs representing Class A ordinary share, ratio			0.25			0.25
Unrealized loss on securities held			$ 249			$ 94
Yanolja | Subsequent Event | Forecast
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Annual Amount		$ 250
Long-term Investments | Investment in private company equity securities
Schedule of Investments [Line Items]
Cost of investment without readily determinable fair values			66			66					$ 552
Investment in equity securities without readily determinable FV			69			69					455
Long-term Investments | Trip.com Group | Convertible Debt Securities
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities											25
Estimated fair value											24
Long-term Investments | Meituan
Schedule of Investments [Line Items]
Carrying Value			2,600			2,600					3,100
Long-term Investments | DiDi Global Inc.
Schedule of Investments [Line Items]
Carrying Value			306			306
Long-term Investments | DiDi Global Inc. | Investment in private company equity securities
Schedule of Investments [Line Items]
Impairment of investment					$ 100
Investment in equity securities without readily determinable FV					$ 400					$ 400	400
Long-term Investments | Yanolja | Investment in private company equity securities
Schedule of Investments [Line Items]
Cost of investment without readily determinable fair values			51			51					51
Long-term Investments | Grab | Redeemable Convertible Preferred Stock
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities			200			200					200
Estimated fair value			330			330					200
Short-term Investments | Trip.com Group | Convertible Debt Securities
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities			525			525					500
Estimated fair value			522			522					501
Short-term Investments | Trip.com Group, Convertible Senior Notes, Issued September 2016 | Convertible Debt Securities
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities			$ 25			$ 25
Term of available-for-sale debt securities			6 years			6 years
Short-term Investments | Trip.com Group, Convertible Senior Notes, Issued December 2015 | Convertible Debt Securities
Schedule of Investments [Line Items]
Amortized cost of available-for-sale debt securities			$ 500			$ 500					$ 500
Term of available-for-sale debt securities			10 years			10 years
[1] See Note 5 for additional information related to the net (losses) gains on equity securities and impairment of investment.

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