Segment Information - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Segment refinery	Sep. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			3
Number of refineries | refinery			6
Income from operations	$ 1,403	$ 1,577	$ 3,554	$ 2,850
Refining Logistics & Fuels Distribution [Member] | Midstream
Segment Reporting Information [Line Items]
Income from operations	230		643
Refining Logistics & Fuels Distribution [Member] | Refining & Marketing
Segment Reporting Information [Line Items]
Income from operations	$ (230)		$ (643)