Revenue Recognition - Disaggregated Operating Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 3,589	$ 3,326	$ 2,060
Total passenger revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	3,509	3,248	2,000
Fare
Disaggregation of Revenue [Line Items]
Total operating revenues	1,277	1,382	806
Total non-fare passenger revenue
Disaggregation of Revenue [Line Items]
Total operating revenues	2,232	1,866	1,194
Service fees
Disaggregation of Revenue [Line Items]
Total operating revenues	943	817	521
Baggage
Disaggregation of Revenue [Line Items]
Total operating revenues	880	741	457
Seat selection
Disaggregation of Revenue [Line Items]
Total operating revenues	281	251	170
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	128	57	46
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 80	$ 78	$ 60