Revenue Recognition - Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Operating revenue	$ 10,472	$ 9,968
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	7,487	7,111
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,316	1,253
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	964	917
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	705	687
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	9,254	8,765
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	6,713	6,282
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,103	1,070
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	855	830
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 583	$ 583