Significant Accounting Policies - Operating Revenue by Principal Geographic Region (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 24,634	$ 15,355	$ 43,259
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Total operating revenue	16,845	9,911	26,960
Atlantic
Disaggregation of Revenue [Line Items]
Total operating revenue	3,414	2,226	7,387
Pacific
Disaggregation of Revenue [Line Items]
Total operating revenue	1,507	1,706	5,132
Latin America
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 2,868	$ 1,512	$ 3,780