Revenue Recognition - Disaggregated Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 967	$ 909	$ 1,815	$ 1,514
Total passenger revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	945	890	1,775	1,478
Fare
Disaggregation of Revenue [Line Items]
Total operating revenues	361	420	664	649
Total non-fare passenger revenue
Disaggregation of Revenue [Line Items]
Total operating revenues	584	470	1,111	829
Service fees
Disaggregation of Revenue [Line Items]
Total operating revenues	245	201	462	363
Baggage
Disaggregation of Revenue [Line Items]
Total operating revenues	232	186	453	316
Seat selection
Disaggregation of Revenue [Line Items]
Total operating revenues	74	68	146	122
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	33	15	50	28
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 22	$ 19	$ 40	$ 36