FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of investment	$ 0		$ 0	$ 100	$ 0
Goodwill	2,412			2,412		$ 2,913
Goodwill, Impairment Loss	0		$ 0	(489)	$ 0
OpenTable And KAYAK [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		$ 1,500
Goodwill, Impairment Loss		(489)		(489)
Investment in private company equity securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of investment		100
Recurring Basis
ASSETS:
Assets at fair value	12,663			12,663		10,751
Recurring Basis | Long-term Investments
ASSETS:
Assets at fair value	250			250		250
Recurring Basis | Money market fund investments | Cash Equivalents
ASSETS:
Assets at fair value	10,089			10,089		5,734
Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Assets at fair value	25			25		29
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 | 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
ASSETS:
Assets at fair value						2
Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	1,795			1,795		1,793
Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value	500			500		767
Recurring Basis | Not Designated as Hedging Instrument | Foreign Currency Contracts
ASSETS:
Assets at fair value	4			4		12
LIABILITIES:
Liabilities at fair value	3			3		5
Nonrecurring Basis
ASSETS:
Assets at fair value	1,945			1,945
Nonrecurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	400	$ 400		400
Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	1,545			1,545
Level 1 | Recurring Basis
ASSETS:
Assets at fair value	11,909			11,909		7,556
Level 1 | Recurring Basis | Long-term Investments
ASSETS:
Assets at fair value	0			0		0
Level 1 | Recurring Basis | Money market fund investments | Cash Equivalents
ASSETS:
Assets at fair value	10,089			10,089		5,734
Level 1 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents
ASSETS:
Assets at fair value	25			25		29
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 | 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
ASSETS:
Assets at fair value						0
Level 1 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	1,795			1,795		1,793
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 Contracts
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 | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	0			0
Level 1 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	0			0
Level 2 | Recurring Basis
ASSETS:
Assets at fair value	504			504		2,945
Level 2 | Recurring Basis | Long-term Investments
ASSETS:
Assets at fair value	0			0		0
Level 2 | Recurring Basis | Money market fund investments | Cash Equivalents
ASSETS:
Assets at fair value	0			0		0
Level 2 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents
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 | 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
ASSETS:
Assets at fair value						2
Level 2 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	0			0		0
Level 2 | Recurring Basis | Trip.com Group | Trip.com Group convertible debt securities | Long-term Investments
ASSETS:
Assets at fair value	500			500		767
Level 2 | Recurring Basis | Not Designated as Hedging Instrument | Foreign Currency Contracts
ASSETS:
Assets at fair value	4			4		12
LIABILITIES:
Liabilities at fair value	3			3		5
Level 2 | Nonrecurring Basis
ASSETS:
Assets at fair value	0			0
Level 2 | Nonrecurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	0			0
Level 2 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	0			0
Level 3 | Recurring Basis
ASSETS:
Assets at fair value	250			250		250
Level 3 | Recurring Basis | Long-term Investments
ASSETS:
Assets at fair value	250			250		250
Level 3 | Recurring Basis | Money market fund investments | Cash Equivalents
ASSETS:
Assets at fair value	0			0		0
Level 3 | Recurring Basis | Time deposits and certificates of deposit | Cash Equivalents
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 | 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
ASSETS:
Assets at fair value						0
Level 3 | Recurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	0			0		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 Contracts
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	1,945			1,945
Level 3 | Nonrecurring Basis | Equity securities | Long-term Investments
ASSETS:
Assets at fair value	400			400
Level 3 | Nonrecurring Basis | Goodwill
ASSETS:
Assets at fair value	$ 1,545			$ 1,545