Revenue Recognition - Passenger Revenue by Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Passenger revenue	$ 8,765	$ 8,178
Domestic
Disaggregation of Revenue [Line Items]
Passenger revenue	6,301	5,894
Atlantic
Disaggregation of Revenue [Line Items]
Passenger revenue	1,059	923
Latin America
Disaggregation of Revenue [Line Items]
Passenger revenue	827	793
Pacific
Disaggregation of Revenue [Line Items]
Passenger revenue	$ 578	$ 568