Revenue Recognition - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Passenger revenue	$ 8,765	$ 8,178
Ticket
Disaggregation of Revenue [Line Items]
Passenger revenue	7,653	7,105
Loyalty travel awards
Disaggregation of Revenue [Line Items]
Passenger revenue	618	582
Travel-related services
Disaggregation of Revenue [Line Items]
Passenger revenue	$ 494	$ 491