FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
LIABILITIES:
Impairment of investment	[1]			$ 0		$ 100		$ 0
Goodwill				2,887	[2]	1,895	[2]	2,913
Impairment of goodwill				0		1,062		$ 0
OpenTable and KAYAK
LIABILITIES:
Goodwill		$ 1,000	$ 1,500
Impairment of goodwill		$ 573	489	0		1,062
Investments in private companies, equity securities | Long-term investments
LIABILITIES:
Carrying Value				325		455
Investments in private companies, equity securities | Long-term investments | Didi Chuxing
LIABILITIES:
Carrying Value			400			400
Impairment of investment			100
Recurring fair value measurements
ASSETS:
Total assets at fair value				13,315		14,054
Recurring fair value measurements | Foreign currency exchange derivatives | Not designated as hedging instrument
ASSETS:
Total assets at fair value				5		9
LIABILITIES:
Total liabilities at fair value				11		7
Recurring fair value measurements | Money market fund investments | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				10,410		10,208
Recurring fair value measurements | Time deposits and certificates of deposit | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				25		32
Recurring fair value measurements | Convertible debt securities | Short-term Investments | Trip.com Group
ASSETS:
Total assets at fair value				25		501
Recurring fair value measurements | Convertible debt securities | Long-term investments | Trip.com Group
ASSETS:
Total assets at fair value						24
Recurring fair value measurements | Investments in private companies, debt securities | Long-term investments
ASSETS:
Total assets at fair value						200
Recurring fair value measurements | Equity securities | Long-term investments
ASSETS:
Total assets at fair value				2,850		3,080
Recurring fair value measurements | Level 1
ASSETS:
Total assets at fair value				13,285		13,320
Recurring fair value measurements | Level 1 | Foreign currency exchange derivatives | Not designated as hedging instrument
ASSETS:
Total assets at fair value				0		0
LIABILITIES:
Total liabilities at fair value				0		0
Recurring fair value measurements | Level 1 | Money market fund investments | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				10,410		10,208
Recurring fair value measurements | Level 1 | Time deposits and certificates of deposit | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				25		32
Recurring fair value measurements | Level 1 | Convertible debt securities | Short-term Investments | Trip.com Group
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 1 | Convertible debt securities | Long-term investments | Trip.com Group
ASSETS:
Total assets at fair value						0
Recurring fair value measurements | Level 1 | Investments in private companies, debt securities | Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements | Level 1 | Equity securities | Long-term investments
ASSETS:
Total assets at fair value				2,850		3,080
Recurring fair value measurements | Level 2
ASSETS:
Total assets at fair value				30		534
Recurring fair value measurements | Level 2 | Foreign currency exchange derivatives | Not designated as hedging instrument
ASSETS:
Total assets at fair value				5		9
LIABILITIES:
Total liabilities at fair value				11		7
Recurring fair value measurements | Level 2 | Money market fund investments | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 2 | Time deposits and certificates of deposit | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 2 | Convertible debt securities | Short-term Investments | Trip.com Group
ASSETS:
Total assets at fair value				25		501
Recurring fair value measurements | Level 2 | Convertible debt securities | Long-term investments | Trip.com Group
ASSETS:
Total assets at fair value						24
Recurring fair value measurements | Level 2 | Investments in private companies, debt securities | Long-term investments
ASSETS:
Total assets at fair value						0
Recurring fair value measurements | Level 2 | Equity securities | Long-term investments
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 3
ASSETS:
Total assets at fair value				0		200
Recurring fair value measurements | Level 3 | Foreign currency exchange derivatives | Not designated as hedging instrument
ASSETS:
Total assets at fair value				0		0
LIABILITIES:
Total liabilities at fair value				0		0
Recurring fair value measurements | Level 3 | Money market fund investments | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 3 | Time deposits and certificates of deposit | Cash equivalents and restricted cash equivalents
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 3 | Convertible debt securities | Short-term Investments | Trip.com Group
ASSETS:
Total assets at fair value				0		0
Recurring fair value measurements | Level 3 | Convertible debt securities | Long-term investments | Trip.com Group
ASSETS:
Total assets at fair value						0
Recurring fair value measurements | Level 3 | Investments in private companies, debt securities | Long-term investments
ASSETS:
Total assets at fair value						200
Recurring fair value measurements | Level 3 | Equity securities | Long-term investments
ASSETS:
Total assets at fair value				0		0
Nonrecurring fair value measurements
ASSETS:
Total assets at fair value						1,404
Nonrecurring fair value measurements | Investments in private companies, equity securities | Long-term investments
ASSETS:
Total assets at fair value				325	[3]	404	[4]
Nonrecurring fair value measurements | Investments in private companies, equity securities | Long-term investments | Didi Chuxing
LIABILITIES:
Carrying Value			$ 400
Nonrecurring fair value measurements | Goodwill | OpenTable and KAYAK
ASSETS:
Total assets at fair value	[5]					1,000
Nonrecurring fair value measurements | Level 1
ASSETS:
Total assets at fair value						0
Nonrecurring fair value measurements | Level 1 | Investments in private companies, equity securities | Long-term investments
ASSETS:
Total assets at fair value				0	[3]	0	[4]
Nonrecurring fair value measurements | Level 1 | Goodwill | OpenTable and KAYAK
ASSETS:
Total assets at fair value	[5]					0
Nonrecurring fair value measurements | Level 2
ASSETS:
Total assets at fair value						0
Nonrecurring fair value measurements | Level 2 | Investments in private companies, equity securities | Long-term investments
ASSETS:
Total assets at fair value				325	[3]	0	[4]
Nonrecurring fair value measurements | Level 2 | Goodwill | OpenTable and KAYAK
ASSETS:
Total assets at fair value	[5]					0
Nonrecurring fair value measurements | Level 3
ASSETS:
Total assets at fair value						1,404
Nonrecurring fair value measurements | Level 3 | Investments in private companies, equity securities | Long-term investments
ASSETS:
Total assets at fair value				$ 0	[3]	404	[4]
Nonrecurring fair value measurements | Level 3 | Goodwill | OpenTable and KAYAK
ASSETS:
Total assets at fair value	[5]					$ 1,000

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

[2] The balance of goodwill as of December 31, 2021 and 2020 is stated net of cumulative impairment charges of $2.0 billion.

[3] During the year ended December 31, 2021, the Company recorded upward adjustments to its investments in equity securities of private companies based on observable price changes in orderly transactions for identical or similar investments of the same issuer (see Note 5).

[4] At March 31, 2020, the investment in DiDi was written down to its estimated fair value of $400 million, resulting in an impairment charge of $100 million (see Note 5).

[5] At March 31, 2020, the goodwill of the OpenTable and KAYAK reporting unit was written down to its estimated fair value of $1.5 billion, resulting in an impairment charge of $489 million. At September 30, 2020, the goodwill was further written down to its estimated fair value of $1.0 billion, resulting in an additional impairment charge of $573 million (see Note 11).