Acquisition - Pro Forma Information - Andeavor (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Sales and other operating revenues	$ 33,547	$ 22,317	$ 61,814	$ 41,183
Net income attributable to MPC	$ 1,106	1,055	$ 1,099	1,092
Andeavor
Business Acquisition [Line Items]
Sales and other operating revenues		34,959		64,338
Net income attributable to MPC		$ 1,452		$ 1,478