INVESTMENTS - Narrative (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
		May 31, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 31, 2019
Schedule of Investments [Line Items]
Net gains (losses) on marketable equity securities	[1]			$ 1,811	$ 745	$ (367)
Impairment of investment	[1]			100	0	0
Short-term Investments
Schedule of Investments [Line Items]
Investment in debt securities					998
Investments in private companies accounted for as debt securities					998
Trip.com Group
Schedule of Investments [Line Items]
Proceeds from sale and maturity of marketable securities				525
Equity securities, net realized loss				201
Equity securities, net unrealized gains					141
Equity securities, net unrealized loss						368
Trip.com Group | Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities					655
Fair value of investment in equity securities					726
Meituan
Schedule of Investments [Line Items]
Equity securities, net unrealized gains				2,000	602	$ 1
Payments to Acquire Other Investments							$ 450
Meituan | Long-term Investments
Schedule of Investments [Line Items]
Fair value of investment in equity securities				3,100	1,100
Government and corporate debt securities
Schedule of Investments [Line Items]
Cash realized from the sales and maturities of investments in debt securities				2,200
Convertible debt securities | Trip.com Group
Schedule of Investments [Line Items]
Investment in debt securities		$ 250		525				$ 500
Proceeds from maturities of debt securities		$ 250
Convertible debt securities | Trip.com Group | Long-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				25	775
Investments in private companies accounted for as debt securities				24	767
Convertible debt securities | Trip.com Group | Short-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				500
Investments in private companies accounted for as debt securities				501
Investments in private companies, equity securities | Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities of private companies				552	501
Fair value of investment in equity securities of private companies				455	501
Investments in private companies, equity securities | Didi Chuxing | Long-term Investments
Schedule of Investments [Line Items]
Investment in equity securities of private companies					500
Fair value of investment in equity securities of private companies			$ 400	400
Impairment of investment			$ 100
Investments in private companies, equity securities | Investment in a private company | Long-term Investments
Schedule of Investments [Line Items]
Fair value of investment in equity securities of private companies				51
Redeemable convertible preferred stock | Long-term Investments
Schedule of Investments [Line Items]
Investment in debt securities				200	250
Investments in private companies accounted for as debt securities				$ 200	$ 250

[1] See Note 5 for additional information related to the net gains (losses) on marketable equity securities and impairment of investment.