Income Per Common Share - Summary of Earnings Per Common Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic earnings per share:
Net income attributable to MPC	$ 855	$ 593	$ 1,054	$ 1,318
Income allocated to participating securities, basic	1	1	2	2
Income available to common stockholders - basic	854	592	1,052	1,316
Weighted average common shares outstanding (in shares)	287	322	290	326
Basic (in USD per share)	$ 2.97	$ 1.84	$ 3.63	$ 4.03
Diluted earnings per share:
Net income attributable to MPC	855	593	1,054	1,318
Income allocated to participating securities, diluted	1	1	2	2
Income available to common stockholders - diluted	$ 854	$ 592	$ 1,052	$ 1,316
Weighted average common shares outstanding (in shares)	287	322	290	326
Effect of dilutive securities (in shares)	2	2	2	2
Weighted average common shares, including dilutive effect (in shares)	289	324	292	328
Diluted (in USD per share)	$ 2.95	$ 1.83	$ 3.60	$ 4.01