Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 11,380	$ 11,003	[1]	$ 32,371	$ 30,812	[1]
Advance Ticket Sales
Revenue From Contract With Customer [Line Items]
Revenue recognized	4,100	4,100		3,400	3,000
Ancillary Fees
Revenue From Contract With Customer [Line Items]
Operating revenue	645	572		1,900	1,600
Frequent Flyer
Revenue From Contract With Customer [Line Items]
Operating revenue	$ 489	$ 480		$ 1,500	$ 1,500

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.