Revenue - Narrative (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Apr. 01, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue From Contract With Customer [Line Items]
Percent of ETCs and FFCs with expiration dates extending beyond 12 months			90.00%		90.00%
Operating revenue			$ 2,489	$ 11,380	$ 11,943	$ 32,371
Advance Ticket Sales
Revenue From Contract With Customer [Line Items]
Expiration period for ETCs	24 months	12 months
Expiration period for FFCs	24 months
ETC and FFC liabilities			3,000		3,000
Revenue recognized			500	4,100	2,900	3,400
Ancillary Fees
Revenue From Contract With Customer [Line Items]
Operating revenue			157	645	699	1,900
Other Operating Revenue
Revenue From Contract With Customer [Line Items]
Operating revenue			418	617	1,460	1,816
Other Operating Revenue | Chase and Other Partner Agreements
Revenue From Contract With Customer [Line Items]
Operating revenue			$ 378	$ 489	$ 1,200	$ 1,500