Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 7,750	$ 2,489	$ 16,442	$ 11,943
Revenue, performance obligation, description of timing			two years
Advance Ticket Sales
Revenue From Contract With Customer [Line Items]
Revenue recognized	2,800	500	$ 1,600	2,900
ETCs and FFCs
Revenue From Contract With Customer [Line Items]
Advance ticket sales liability	3,000		3,000
Ancillary Fees
Revenue From Contract With Customer [Line Items]
Operating revenue	707	205	1,500	981
Other Operating Revenue
Revenue From Contract With Customer [Line Items]
Operating revenue	594	418	1,501	1,460
Other Operating Revenue | Chase and Other Partner Agreements
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 484	$ 378	$ 1,300	$ 1,200