Revenue Recognition - Passenger Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Operating revenue	$ 11,953	$ 11,061	$ 33,696	$ 30,910
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	10,796	9,979	30,107	27,925
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	7,395	6,775	21,093	19,521
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,996	1,802	4,837	4,297
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	675	693	2,228	2,226
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 730	$ 709	$ 1,949	$ 1,881