Revenue Recognition - Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Operating revenue	$ 12,536	$ 11,775	$ 23,008	$ 21,743
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	8,787	8,244	16,274	15,355
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	2,136	1,997	3,452	3,250
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	838	791	1,802	1,708
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	775	743	1,480	1,430
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	11,368	10,546	20,622	19,311
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	8,071	7,416	14,784	13,697
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,880	1,771	2,983	2,841
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	760	722	1,615	1,553
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 657	$ 637	$ 1,240	$ 1,220