Segments - Schedule of Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information, Profit (Loss)
Operating revenue	$ 11,775	$ 10,747	$ 21,743	$ 19,848
Operating income	1,680	1,982	2,520	2,981
Interest expense (income), net	89	103	191	197
Depreciation and amortization	590	531	1,200	1,068
Total assets, end of period	55,796	52,451	55,796	52,451	$ 53,711
Capital expenditures	1,580	988	2,846	1,790
Operating Segments | Airline
Segment Reporting Information, Profit (Loss)
Operating revenue	11,559	10,680	21,314	19,720
Operating income	1,635	1,976	2,431	2,931
Interest expense (income), net	97	103	203	197
Depreciation and amortization	573	520	1,168	1,047
Total assets, end of period	53,335	50,964	53,335	50,964
Capital expenditures	1,567	928	2,818	1,704
Operating Segments | Refinery
Segment Reporting Information, Profit (Loss)
Operating revenue	1,667	1,139	3,158	2,267
Operating income	45	6	89	50
Interest expense (income), net	(8)	0	(12)	0
Depreciation and amortization	17	11	32	21
Total assets, end of period	2,461	1,487	2,461	1,487
Capital expenditures	13	60	28	86
Intersegment Sales/Other | Sales to airline segment
Segment Reporting Information, Profit (Loss)
Operating revenue	(275)	(193)	(537)	(383)
Intersegment Sales/Other | Exchanged products
Segment Reporting Information, Profit (Loss)
Operating revenue	(1,096)	(756)	(1,972)	(1,489)
Intersegment Sales/Other | Sales of refined products
Segment Reporting Information, Profit (Loss)
Operating revenue	$ (80)	$ (123)	$ (220)	$ (267)