Segment Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended			3 Months Ended				9 Months Ended				3 Months Ended				9 Months Ended				3 Months Ended				6 Months Ended	9 Months Ended				3 Months Ended				9 Months Ended
	Jul. 31, 2012 Store	May 31, 2012 Store	May 31, 2011 Store	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012 Segment		Sep. 30, 2011		Sep. 30, 2012 Refining & Marketing [Member]		Sep. 30, 2011 Refining & Marketing [Member]		Sep. 30, 2012 Refining & Marketing [Member]		Sep. 30, 2011 Refining & Marketing [Member]		Sep. 30, 2012 Speedway [Member]		Sep. 30, 2011 Speedway [Member]		Jun. 30, 2012 Speedway [Member] Store	Sep. 30, 2012 Speedway [Member] Store		Sep. 30, 2011 Speedway [Member]		Sep. 30, 2012 Pipeline Transportation [Member]		Sep. 30, 2011 Pipeline Transportation [Member]		Sep. 30, 2012 Pipeline Transportation [Member]		Sep. 30, 2011 Pipeline Transportation [Member]
Segment Reporting Information [Line Items]
Number of reportable segments								3
Customer				$ 21,048		$ 20,614		$ 61,554		$ 59,165		$ 17,242		$ 16,929		$ 50,794		$ 48,883		$ 3,787		$ 3,668			$ 10,703		$ 10,236		$ 19		$ 17		$ 57		$ 46
Intersegment				2,485	[1]	2,403	[2]	6,829	[2]	6,581	[2]	2,387	[1]	2,313	[2]	6,560	[2]	6,327	[2]	1	[1]				3	[2]			97	[1]	90	[2]	266	[2]	254	[2]
Related parties				2		2		6		53		2		2		5		51															1		2
Segment revenues				23,535		23,019		68,389		65,799		19,631		19,244		57,359		55,261		3,788		3,668			10,706		10,236		116		107		324		302
Elimination of intersegment revenues				(2,485)		(2,403)		(6,829)		(6,581)		(2,387)		(2,313)		(6,560)		(6,327)		(1)					(3)				(97)		(90)		(266)		(254)
Total revenues				21,050		20,616		61,560		59,218		17,244		16,931		50,799		48,934		3,787		3,668			10,703		10,236		19		17		58		48
Segment income from operations				1,819		1,852		4,336		4,132		1,691		1,711		3,959		3,773		76		85			233		198		52		56		144		161
Income (loss) from equity method investments				7		15		18		41		(1)		5		(2)		9											8		10		20		32
Depreciation and amortization				240	[3]	219	[3]	695	[3]	650	[3]	198	[3]	179	[3]	574	[3]	534	[3]	29	[3]	28	[3]		84	[3]	82	[3]	13	[3]	12	[3]	37	[3]	34	[3]
Capital expenditures and investments				$ 312	[4],[5]	$ 274	[4],[5],[6]	$ 939	[4],[5],[6]	$ 790	[4],[7]	$ 182	[4],[5]	$ 224	[4],[5],[6]	$ 513	[4],[5],[6]	$ 600	[4],[7]	$ 59	[4],[5],[8]	$ 19	[4],[5],[6],[8]		$ 257	[4],[5],[6],[8]	$ 121	[4],[7],[8]	$ 71	[4],[5]	$ 31	[4],[5],[6]	$ 169	[4],[5],[6]	$ 69	[4],[7]
Number of convenience stores acquired	10	87	23																					87	10

[1] Corporate and other unallocated items consists primarily of MPC's corporate administrative expenses, including allocations from the Marathon Oil Companies for periods prior to the Spinoff and costs related to certain non-operating assets.

[2] Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties.

[3] Differences between segment totals and MPC totals represent amounts related to unallocated items and are included in "Items not allocated to segments" in the reconciliation below.

[4] Capital expenditures include changes in capital accruals.

[5] Includes Speedway's acquisition of 10 convenience stores in July 2012.

[6] Includes Speedway's acquisition of 87 convenience stores in May 2012.

[7] Includes Speedway's acquisition of 23 convenience stores in May 2011.

[8] Includes acquisitions of 10 convenience stores in July 2012, 87 convenience stores in May 2012 and 23 convenience stores in May 2011.