Income Per Common Share - Summary of Earnings Per Common Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic earnings per share:
Net income attributable to MPC	$ 672	$ 168	$ 1,726	$ 1,486
Income allocated to participating securities, basic	1	0	3	2
Income available to common stockholders - basic	671	168	1,723	1,484
Weighted average common shares outstanding (in shares)	282	309	288	321
Basic (in USD per share)	$ 2.38	$ 0.54	$ 5.99	$ 4.63
Diluted earnings per share:
Net income attributable to MPC	672	168	1,726	1,486
Income allocated to participating securities, diluted	1	0	3	2
Income available to common stockholders - diluted	$ 671	$ 168	$ 1,723	$ 1,484
Weighted average common shares outstanding (in shares)	282	309	288	321
Effect of dilutive securities (in shares)	2	2	2	2
Weighted average common shares, including dilutive effect (in shares)	284	311	290	323
Diluted (in USD per share)	$ 2.36	$ 0.54	$ 5.95	$ 4.60