Segments and Geographic Information - Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Operating revenue	$ 9,458	$ 10,483	$ 10,447	$ 9,251	$ 9,502	$ 11,107	$ 10,707	$ 9,388	$ 39,639	$ 40,704	$ 40,362
Domestic
Revenues
Operating revenue									28,108	27,884	26,898
Atlantic
Revenues
Operating revenue									5,919	6,505	6,757
Pacific
Revenues
Operating revenue									2,939	3,503	3,948
Latin America
Revenues
Operating revenue									$ 2,673	$ 2,812	$ 2,759