Revenue - Operating Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Operating revenue	$ 7,750	$ 2,489	$ 16,442	$ 11,943
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue	5,412	1,672	11,290	7,675
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,116	365	2,111	1,799
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	373	282	1,073	1,346
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	$ 849	$ 170	$ 1,968	$ 1,123