CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common stock	Common stock Class B Common Stock	Additional paid-in capital	Treasury stock	Retained earnings (deficit)	Accumulated other comprehensive income (loss)	Non-redeemable non-controlling interest
Beginning Balance (in shares) at Dec. 31, 2015		220,383,124	12,799,999		82,923,771
Beginning Balance at Dec. 31, 2015	$ 4,930	$ 0	$ 0	$ 8,697	$ (4,055)	$ 508	$ (285)	$ 65
Net income (excludes net income (loss) attributable to redeemable non-controlling interest)	284					282		2
Other comprehensive income (loss), net of taxes	(1)						(1)	0
Proceeds from exercise of equity instruments and employee stock purchase plans (in shares)		3,413,505
Proceeds from exercise of equity instruments and employee stock purchase plans	141	$ 0		141
Withholding taxes for stock options	(1)			(1)
Issuance of common stock in connection with acquisitions (in shares)		513,140
Issuance of common stock in connection with acquisitions	0	$ 0		0
Treasury stock activity related to vesting of equity instruments (in shares)					174,378
Treasury stock activity related to vesting of equity instruments	$ (20)				$ (20)
Common stock repurchases (in shares)	3,979,170				3,979,170
Common stock repurchases	$ (436)				$ (436)
Payment of dividends to stockholders (declared at $1.00 per share)	(150)			0		(150)
Adjustment to the fair value of redeemable non-controlling interests	848			344		504
Change in ownership of non-controlling interest related to trivago initial public offering (IPO)	0			32			6	26
Transfer from redeemable non-controlling interests	1,381			0				1,381
Proceeds related to trivago IPO, net of fees and expenses	210			125				85
Stock-based compensation expense	196			196
Other	4			2				2
Ending Balance (in shares) at Dec. 31, 2016		224,309,769	12,799,999		87,077,319
Ending Balance at Dec. 31, 2016	5,693	$ 0	$ 0	8,794	$ (4,511)	129	(280)	1,561
Impact of adoption of new accounting guidance related to stock-based compensation	3			10		(7)
Net income (excludes net income (loss) attributable to redeemable non-controlling interest)	369					378		(9)
Other comprehensive income (loss), net of taxes	182						131	51
Proceeds from exercise of equity instruments and employee stock purchase plans (in shares)		3,982,546
Proceeds from exercise of equity instruments and employee stock purchase plans	228	$ 0		228
Withholding taxes for stock options	(9)			(9)
Issuance of common stock in connection with acquisitions (in shares)		175,040
Issuance of common stock in connection with acquisitions	0	$ 0		0
Treasury stock activity related to vesting of equity instruments (in shares)					133,319
Treasury stock activity related to vesting of equity instruments	$ (17)				$ (17)
Common stock repurchases (in shares)	2,317,617				2,317,617
Common stock repurchases	$ (294)				$ (294)
Payment of dividends to stockholders (declared at $1.00 per share)	(176)			0		(176)
Other changes in non-controlling interests	6			3				3
Stock-based compensation expense	148			148
Other	(1)			(1)
Ending Balance (in shares) at Dec. 31, 2017		228,467,355	12,799,999		89,528,255
Ending Balance at Dec. 31, 2017	6,129	$ 0	$ 0	9,163	$ (4,822)	331	(149)	1,606
Net income (excludes net income (loss) attributable to redeemable non-controlling interest)	397					406		(9)
Other comprehensive income (loss), net of taxes	(86)						(68)	(18)
Proceeds from exercise of equity instruments and employee stock purchase plans (in shares)		2,850,591
Proceeds from exercise of equity instruments and employee stock purchase plans	166	$ 0		166
Withholding taxes for stock options	(2)			(2)
Issuance of common stock in connection with acquisitions (in shares)		175,040
Issuance of common stock in connection with acquisitions	0	$ 0		0
Treasury stock activity related to vesting of equity instruments (in shares)					179,783
Treasury stock activity related to vesting of equity instruments	$ (20)				$ (20)
Common stock repurchases (in shares)	7,720,194				7,720,194
Common stock repurchases	$ (904)				$ (904)
Proceeds from issuance of treasury stock (in shares)					269,646
Proceeds from issuance of treasury stock	31			27	$ 4
Payment of dividends to stockholders (declared at $1.00 per share)	(186)					(186)
Adjustment to the fair value of redeemable non-controlling interests	(3)			0		(3)
Other changes in non-controlling interests	18			(7)				25
Purchase of remaining interest in Air Asia	(62)			(5)				(57)
Stock-based compensation expense	208			208
Other	(1)			(1)
Ending Balance (in shares) at Dec. 31, 2018		231,492,986	12,799,999		97,158,586
Ending Balance at Dec. 31, 2018	$ 5,651	$ 0	$ 0	$ 9,549	$ (5,742)	$ 517	$ (220)	$ 1,547