Segments - Schedule of Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information, Profit (Loss)
Operating revenue	$ 11,953	$ 11,061	$ 33,696	$ 30,910
Operating income	1,642	1,823	4,161	4,805
Interest expense (income), net	84	100	274	297
Depreciation and amortization	580	571	1,780	1,639
Total assets, end of period	55,003	52,575	55,003	52,575	$ 53,711
Capital expenditures	967	941	3,813	2,731
Operating Segments | Airline
Segment Reporting Information, Profit (Loss)
Operating revenue	11,845	10,932	33,159	30,653
Operating income	1,630	1,786	4,060	4,718
Interest expense (income), net	94	100	297	297
Depreciation and amortization	564	560	1,732	1,607
Total assets, end of period	53,103	50,639	53,103	50,639
Capital expenditures	928	901	3,746	2,605
Operating Segments | Refinery
Segment Reporting Information, Profit (Loss)
Operating revenue	1,609	1,357	4,767	3,624
Operating income	12	37	101	87
Interest expense (income), net	(10)	0	(23)	0
Depreciation and amortization	16	11	48	32
Total assets, end of period	1,900	1,936	1,900	1,936
Capital expenditures	39	40	67	126
Intersegment Sales/Other | Sales to airline segment
Segment Reporting Information, Profit (Loss)
Operating revenue	(328)	(239)	(866)	(622)
Intersegment Sales/Other | Exchanged products
Segment Reporting Information, Profit (Loss)
Operating revenue	(1,110)	(910)	(3,081)	(2,399)
Intersegment Sales/Other | Sales of refined products
Segment Reporting Information, Profit (Loss)
Operating revenue	$ (63)	$ (79)	$ (283)	$ (346)