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Investment in Other Companies (Details) (USD $)
In Millions, unless otherwise specified
1 Months Ended 1 Months Ended 12 Months Ended
Sep. 30, 2008
Trip
Dec. 31, 2011
Trip
Sep. 30, 2008
Trip
Preferred stock
Sep. 30, 2008
Trip
Common stock
Sep. 30, 2010
Air Mekong
Dec. 31, 2011
Air Mekong
Investment in Other Companies            
Percentage ownership acquired     6.00% 20.00% 30.00%  
Payments to acquire equity method investment         $ 7 $ 3
Carrying amount of equity method investment   28.5       2.9
Voting ownership interest (as a percent)   20.00%        
The annual rate of return used to calculate the put option price (as a percent) 5.00%          
Income from equity method investment           $ 13.3