Supplementary Statistics (Operating Statistics) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012 MBPD		Sep. 30, 2011 MBPD		Sep. 30, 2012 MBPD		Sep. 30, 2011 MBPD
Operating Statistics [Line Items ]
MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)	1,622	[1]	1,625	[1]	1,590	[1]	1,589	[1]
Refining & Marketing [Member]
Refinery Throughputs (thousands of barrels per day):
Crude oil refined	1,186		1,201		1,180		1,171
Other charge and blendstocks	159		167		155		183
Total	1,345		1,368		1,335		1,354
Crude Oil Capacity Utilization percent	99.00%	[2]	105.00%	[2]	99.00%	[2]	103.00%	[2]
Refined Product Yields (thousands of barrels per day):
Gasoline	728		724		723		733
Distillates	439		433		420		424
Propane	25		25		25		25
Feedstocks and special products	95		122		109		118
Heavy fuel oil	21		19		18		20
Asphalt	67		63		64		57
Total	1,375		1,386		1,359		1,377
Refining & Marketing Refined Product Sales Volume (thousands of barrels per day)	1,605	[3]	1,610	[3]	1,569	[3]	1,571	[3]
Refining & Marketing Gross Margin (dollars per barrel)	13.12	[4]	13.18	[4]	10.92	[4]	10.30	[4]
Planned turnaround and major maintenance	1.18		0.36		1.04		0.74
Depreciation and amortization	1.44		1.28		1.40		1.29
Other manufacturing	3.16	[5]	3.11	[5]	3.13	[5]	3.19	[5]
Total	5.78		4.75		5.57		5.22
Speedway [Member]
Refined Product Yields (thousands of barrels per day):
Convenience stores at period-end	1,463		1,374		1,463		1,374
Gasoline & distillates sales (millions of gallons)	779		775		2,241		2,193
Gasoline & distillates gross margin (dollars per gallon)	0.1100	[6]	0.1257	[6]	0.1281	[6]	0.1277	[6]
Merchandise sales (in millions)	826		797		2,297		2,203
Merchandise gross margin (in millions)	217		200		599		536
Pipeline Transportation [Member]
Pipeline throughput (thousands of barrels per day):
Crude oil pipelines	1,136		1,205		1,150		1,200
Refined products pipelines	1,044		1,128		972		1,039
Total	2,180		2,333		2,122		2,239

[1] Total average daily volumes of refined product sales to wholesale, branded and retail (Speedway segment) customers.

[2] Based on calendar day capacity, which is an annual average that includes downtime for planned maintenance and other normal operating activities.

[3] Includes intersegment sales.

[4] Sales revenue less cost of refinery inputs, purchased products and manufacturing expenses, including depreciation and amortization, divided by Refining & Marketing segment refined product sales volume.

[5] Includes utilities, labor, routine maintenance and other operating costs.

[6] The price paid by consumers less the cost of refined products, including transportation and consumer excise taxes, and the cost of bankcard processing fees, divided by gasoline and distillates sales volume.