Revenue - Operating Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Operating revenue	$ 11,380	$ 11,003	[1]	$ 32,371	$ 30,812	[1]
Domestic (U.S. and Canada)
Disaggregation of Revenue [Line Items]
Operating revenue	7,094	6,762		20,056	18,927
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	2,103	2,073		5,627	5,427
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	1,280	1,339		3,867	3,855
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	$ 903	$ 829		$ 2,821	$ 2,603

[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.