Segment Information - Revenue by Services and Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 2,319,208	$ 2,965,848	$ 2,586,052	$ 2,188,736	$ 2,092,829	$ 2,580,905	$ 2,195,869	$ 1,903,961	$ 10,059,844	$ 8,773,564	$ 6,672,317
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									5,534,466	5,036,539	3,703,302
All other countries
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									4,525,378	3,737,025	2,969,015
Lodging
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									6,851,171	6,020,668	4,638,481
Advertising and media
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									1,072,656	807,383	565,704
Air
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									783,573	777,696	566,123
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									$ 1,352,444	$ 1,167,817	$ 902,009