Segments and Geographic Information - Schedule of Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information, Profit (Loss)
Operating revenue	$ 10,245	$ 11,060	$ 10,791	$ 9,148	$ 9,458	$ 10,483	$ 10,447	$ 9,251	$ 41,244	$ 39,639	$ 40,704
Operating income (loss)	1,193	$ 1,839	$ 2,028	$ 1,053	1,020	$ 1,969	$ 2,423	$ 1,540	6,114	6,952	7,802
Interest expense (income), net									396	388	481
Depreciation and amortization									2,235	1,902	1,835
Total assets	53,292				51,261				53,292	51,261	53,134
Capital expenditures									3,891	3,391	2,945
Operating Segments | Airline
Segment Reporting Information, Profit (Loss)
Operating revenue									40,742	39,406	40,398
Operating income (loss)									6,004	7,077	7,512
Interest expense (income), net									403	386	481
Depreciation and amortization									2,188	1,862	1,805
Total assets	51,165				49,930				51,165	49,930	51,785
Capital expenditures									3,743	3,270	2,853
Operating Segments | Refinery
Segment Reporting Information, Profit (Loss)
Operating revenue									5,039	3,843	4,741
Operating income (loss)									110	(125)	290
Interest expense (income), net									(7)	2	0
Depreciation and amortization									47	40	30
Total assets	$ 2,127				$ 1,331				2,127	1,331	1,349
Capital expenditures									148	121	92
Intersegment Sales/Other | Sales to airline segment
Segment Reporting Information, Profit (Loss)
Operating revenue									(886)	(695)	(990)
Intersegment Sales/Other | Exchanged products
Segment Reporting Information, Profit (Loss)
Operating revenue									(3,240)	(2,658)	(3,108)
Intersegment Sales/Other | Sales of refined products
Segment Reporting Information, Profit (Loss)
Operating revenue									$ (411)	$ (257)	$ (337)