FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
LIABILITIES:
Impairment of investment		$ 0		$ 0	$ 100	$ 0
Goodwill	[1]	1,865			1,865		$ 2,913
Goodwill impairment charge		(573)		$ 0	(1,062)	$ 0
OpenTable And KAYAK
LIABILITIES:
Goodwill		1,000	$ 1,500		1,000
Goodwill impairment charge		(573)	(489)		(1,062)
Didi Chuxing | Investment in private company equity securities | Long-term Investments
LIABILITIES:
Impairment of investment			100
Recurring Basis
ASSETS:
Assets at fair value		14,171			14,171		10,751
Recurring Basis | Money market fund investments | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		10,874			10,874		5,734
Recurring Basis | Corporate debt securities | Short-term Investments
ASSETS:
Assets at fair value							751
Recurring Basis | Corporate debt securities | Long-term Investments
ASSETS:
Assets at fair value							963
Recurring Basis | Corporate debt securities | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value							2
Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		19			19		29
Recurring Basis | Investments in private company debt securities | Long-term Investments
ASSETS:
Assets at fair value		250			250		250
Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value		2,525			2,525		1,793
Recurring Basis | International government securities | Short-term Investments
ASSETS:
Assets at fair value							109
Recurring Basis | International government securities | Long-term Investments
ASSETS:
Assets at fair value							68
Recurring Basis | U.S. government securities | Short-term Investments
ASSETS:
Assets at fair value							138
Recurring Basis | U.S. government securities | Long-term Investments
ASSETS:
Assets at fair value							135
Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value		493			493		767
Recurring Basis | Not Designated as Hedging Instrument | Foreign currency exchange derivatives
ASSETS:
Assets at fair value		10			10		12
LIABILITIES:
Liabilities at fair value		13			13		5
Nonrecurring Basis
ASSETS:
Assets at fair value		1,404			1,404
Nonrecurring Basis | Investment in private company equity securities | Long-term Investments
ASSETS:
Assets at fair value	[2]	404			404
Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	[3]	1,000			1,000
Nonrecurring Basis | Didi Chuxing | Investment in private company equity securities | Long-term Investments
ASSETS:
Assets at fair value			$ 400
Level 1 | Recurring Basis
ASSETS:
Assets at fair value		13,418			13,418		7,556
Level 1 | Recurring Basis | Money market fund investments | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		10,874			10,874		5,734
Level 1 | Recurring Basis | Corporate debt securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | Corporate debt securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | Corporate debt securities | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		19			19		29
Level 1 | Recurring Basis | Investments in private company debt securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 1 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value		2,525			2,525		1,793
Level 1 | Recurring Basis | International government securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | International government securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | U.S. government securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | U.S. government securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 1 | Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 1 | Recurring Basis | Not Designated as Hedging Instrument | Foreign currency exchange derivatives
ASSETS:
Assets at fair value		0			0		0
LIABILITIES:
Liabilities at fair value		0			0		0
Level 1 | Nonrecurring Basis
ASSETS:
Assets at fair value		0			0
Level 1 | Nonrecurring Basis | Investment in private company equity securities | Long-term Investments
ASSETS:
Assets at fair value	[2]	0			0
Level 1 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	[3]	0			0
Level 2 | Recurring Basis
ASSETS:
Assets at fair value		503			503		2,945
Level 2 | Recurring Basis | Money market fund investments | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		0			0		0
Level 2 | Recurring Basis | Corporate debt securities | Short-term Investments
ASSETS:
Assets at fair value							751
Level 2 | Recurring Basis | Corporate debt securities | Long-term Investments
ASSETS:
Assets at fair value							963
Level 2 | Recurring Basis | Corporate debt securities | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value							2
Level 2 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		0			0		0
Level 2 | Recurring Basis | Investments in private company debt securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 2 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 2 | Recurring Basis | International government securities | Short-term Investments
ASSETS:
Assets at fair value							109
Level 2 | Recurring Basis | International government securities | Long-term Investments
ASSETS:
Assets at fair value							68
Level 2 | Recurring Basis | U.S. government securities | Short-term Investments
ASSETS:
Assets at fair value							138
Level 2 | Recurring Basis | U.S. government securities | Long-term Investments
ASSETS:
Assets at fair value							135
Level 2 | Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value		493			493		767
Level 2 | Recurring Basis | Not Designated as Hedging Instrument | Foreign currency exchange derivatives
ASSETS:
Assets at fair value		10			10		12
LIABILITIES:
Liabilities at fair value		13			13		5
Level 2 | Nonrecurring Basis
ASSETS:
Assets at fair value		0			0
Level 2 | Nonrecurring Basis | Investment in private company equity securities | Long-term Investments
ASSETS:
Assets at fair value	[2]	0			0
Level 2 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	[3]	0			0
Level 3 | Recurring Basis
ASSETS:
Assets at fair value		250			250		250
Level 3 | Recurring Basis | Money market fund investments | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		0			0		0
Level 3 | Recurring Basis | Corporate debt securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | Corporate debt securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | Corporate debt securities | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents and Restricted Cash Equivalents
ASSETS:
Assets at fair value		0			0		0
Level 3 | Recurring Basis | Investments in private company debt securities | Long-term Investments
ASSETS:
Assets at fair value		250			250		250
Level 3 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 3 | Recurring Basis | International government securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | International government securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | U.S. government securities | Short-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | U.S. government securities | Long-term Investments
ASSETS:
Assets at fair value							0
Level 3 | Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value		0			0		0
Level 3 | Recurring Basis | Not Designated as Hedging Instrument | Foreign currency exchange derivatives
ASSETS:
Assets at fair value		0			0		0
LIABILITIES:
Liabilities at fair value		0			0		$ 0
Level 3 | Nonrecurring Basis
ASSETS:
Assets at fair value		1,404			1,404
Level 3 | Nonrecurring Basis | Investment in private company equity securities | Long-term Investments
ASSETS:
Assets at fair value	[2]	404			404
Level 3 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	[3]	$ 1,000			$ 1,000

[1] (1) The balance of goodwill as of September 30, 2020 and December 31, 2019 is stated net of cumulative impairment charges of $2.0 billion and $941 million, respectively.

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

[3] (2) 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 8).