Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009
Significant Accounting Policies [Line Items]
Definite lived intangible assets, estimated useful life, minimum		1
Definite lived intangible assets, estimated useful life, maximum		12
Advertising expense		$ 796	$ 694	$ 622
Prepaid marketing expenses		$ 11	$ 14
EXPE's percentage of third party service provider total revenue	39.00%		44.00%
Computer Equipment [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum		3
Property and equipment, estimated useful lives, maximum		5
Software Development [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum		3
Property and equipment, estimated useful lives, maximum		5
Furniture and Fixtures [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum		3
Property and equipment, estimated useful lives, maximum		5
Stock Options [Member]
Significant Accounting Policies [Line Items]
Vesting period		four
Restricted Stock Units (RSUs) [Member]
Significant Accounting Policies [Line Items]
Vesting period		five
AirAsia Joint Venture [Member]
Significant Accounting Policies [Line Items]
Owned equity investments		50.00%