Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
City of San Francisco
Loss Contingencies [Line Items]
Tax assessments including interest and penalties	$ 22
Litigation relating to occupancy tax
Loss Contingencies [Line Items]
Number of lawsuits filed by cities, counties and states involving hotel occupancy taxes	80
Number of lawsuits currently active	44
Number of lawsuits dismissed to date	30
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	18
Reserve for potential settlement of issues related to hotel occupancy taxes	36	32
Accrual related to court decisions and final settlements related to hotel occupancy taxes		10
Occupancy tax assessments tax payment (refund)		$ (3)	$ 3	$ 48
Matters relating to hotel booking practices
Loss Contingencies [Line Items]
Number of Putative class action law suits	21