Revenue - Operating Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Operating revenue	$ 2,489	$ 11,380	$ 11,943	$ 32,371
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue	1,672	7,094	7,675	20,056
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	365	2,103	1,799	5,627
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	282	1,280	1,346	3,867
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	$ 170	$ 903	$ 1,123	$ 2,821