Acquisitions and Investments Acquisition and Investments (Schedule of Acquisition Related Pro Forma Financial Information) (Details) (Galveston Bay Refinery and Related Assets, USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Galveston Bay Refinery and Related Assets
Business Acquisition [Line Items]
Sales and other operating revenues (including consumer excise taxes)	$ 50,975
Net income attributable to MPC	$ 1,373
Net income attributable to MPC per share - basic	$ 4.21
Net income attributable to MPC per share - diluted	$ 4.19