Commitments and Contingencies - Litigation (Details) $ in Millions				1 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) lawsuit jurisdiction item	May 15, 2017 USD ($)	Aug. 01, 2015	Sep. 30, 2015 USD ($)	May 31, 2014 USD ($)	Mar. 31, 2018 USD ($) lawsuit jurisdiction item	Dec. 31, 2017 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2009 USD ($)
Expedia | Occupancy Tax Litigation
Loss Contingencies [Line Items]
Number of lawsuits filed by cities, counties and states involving hotel occupancy taxes | lawsuit	96					96
Number of lawsuits currently active | lawsuit	15					15
Number of lawsuits dismissed to date | lawsuit	42
Number of dismissals based on finding that defendant was not subject to local hotel occupancy tax or the local government lacked standing to pursue claims | item	28
Loss contingency reserve	$ 45.0					$ 45.0
Loss contingency estimated loss	23.0					23.0
Loss contingency estimated maximum interest payable	$ 57.0					$ 57.0
Number of jurisdictions in which interest may be payable | jurisdiction	1					1
Expedia | Hawaii General Excise Tax Litigation
Loss Contingencies [Line Items]
Proceeds from tax refund				$ 132.0
Tax paid, net of refunds								$ 171.0
Expected Occupancy And Other Tax Assessment Payments		$ 16.7
Expedia | San Francisco Occupancy Tax Litigation [member]
Loss Contingencies [Line Items]
Occupancy And Other Tax Assessment Payments					$ 25.5				$ 48.0
Expedia | Competition Reviews And Legislation Relating To Parity Clauses
Loss Contingencies [Line Items]
Period when certain parity clauses were waived			5 years
Number of Italian hotel trade associations appealing the case closure | item	2					2
Number of NCA's in working group to monitor online hotel bookings | item	10					10
Orbitz Worldwide Inc | Hawaii General Excise Tax Litigation
Loss Contingencies [Line Items]
Proceeds from tax refund				$ 22.0
Orbitz Worldwide Inc | San Francisco Occupancy Tax Litigation [member]
Loss Contingencies [Line Items]
Occupancy And Other Tax Assessment Payments						$ 4.6
Expedia and Orbitz [member] | Hawaii General Excise Tax Litigation
Loss Contingencies [Line Items]
Tax paid, net of refunds							$ 44.0