Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 5,471	$ 1,475	$ 8,692	$ 9,454
Advance Ticket Sales
Revenue From Contract With Customer [Line Items]
Revenue recognized	1,500	500	1,400	2,800
ETCs and FFCs
Revenue From Contract With Customer [Line Items]
Advance ticket sales liability	2,600		2,600
Ancillary Fees
Revenue From Contract With Customer [Line Items]
Operating revenue	499	71	807	776
Other Operating Revenue
Revenue From Contract With Customer [Line Items]
Operating revenue	499	392	907	1,042
Other Operating Revenue | Chase and Other Partner Agreements
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 449	$ 339	$ 811	$ 869