Significant Accounting Policies - Operating Revenue by Principal Geographic Region (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 53,717	$ 44,955	$ 24,634
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Total operating revenue	32,400	28,474	16,845
Atlantic
Disaggregation of Revenue [Line Items]
Total operating revenue	10,982	9,072	3,414
Pacific
Disaggregation of Revenue [Line Items]
Total operating revenue	5,267	2,927	1,507
Latin America
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 5,068	$ 4,482	$ 2,868