Revenue - Operating Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Operating revenue	$ 1,475	$ 11,402	$ 9,454	$ 20,991
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue	925	7,087	6,003	12,962
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	219	2,066	1,434	3,524
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	258	1,306	1,064	2,587
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	$ 73	$ 943	$ 953	$ 1,918