Revenue Recognition - Disaggregated Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 909	$ 550	$ 1,514	$ 821
Total passenger revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	890	536	1,478	798
Fare
Disaggregation of Revenue [Line Items]
Total operating revenues	420	214	649	314
Total non-fare passenger revenue
Disaggregation of Revenue [Line Items]
Total operating revenues	470	322	829	484
Service fees
Disaggregation of Revenue [Line Items]
Total operating revenues	201	142	363	204
Baggage
Disaggregation of Revenue [Line Items]
Total operating revenues	186	123	316	190
Seat selection
Disaggregation of Revenue [Line Items]
Total operating revenues	68	47	122	71
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	15	10	28	19
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 19	$ 14	$ 36	$ 23