Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Realized and Unrealized Before-Tax Gain / (Loss) on Derivative Instruments Recognized in the Consolidated Statement of Income
Sales and other operating revenue	$ 67,491	$ 71,456	$ 129,137	$ 136,892
Crude oil and product purchases	38,942	41,327	73,743	77,615
Not Designated as Hedging Instrument [Member]
Realized and Unrealized Before-Tax Gain / (Loss) on Derivative Instruments Recognized in the Consolidated Statement of Income
Sales and other operating revenue	33	(11)	(242)	(3)
Crude oil and product purchases	33	(193)	15	(274)
Total	$ 66	$ (204)	$ (227)	$ (277)