Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss on minority equity investments, net			$ 61	$ 6
Net gains (losses) from foreign currency forward contracts	$ 33	$ 14	48	9
Impairment of goodwill	61	$ 0	61	$ 0
Goodwill	8,139		8,139		$ 8,229
Carrying value of cost method investments	374		374		371
Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount of foreign currency derivatives	3,300		3,300
Recurring Basis | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net forward asset	38		38		6
Despegar.com
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss on minority equity investments, net			62
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross unrealized loss					9
Available-for-sale Securities | Despegar.com
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities					273
Gross unrealized loss					$ 9
Reporting Unit Within Core Online Travel Companies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of goodwill	61
Core OTA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	$ 25		$ 25