Segment Information (Income From Operations Attributable To Operating Segments) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Customer									$ 100,152		$ 82,235		$ 78,583
Related parties									8		8		55
Segment income from operations	1,008	301	960	1,156	1,189	1,895	1,307	956	3,425		5,347		3,745
Income (loss) from equity method investments									36		26		50
Depreciation and amortization									1,220		995		891
Capital expenditures and investments									2,789	[1],[2]	1,460	[1],[2]	1,323	[1],[2]
Acquisitions									1,386	[3]	180	[3]	74	[3]
Galveston Bay Refinery And Related Assets [Member]
Segment Reporting Information [Line Items]
Acquisitions									1,360
Operating Segments [Member]
Segment Reporting Information [Line Items]
Customer									100,158		82,237		78,583
Intersegment									9,756	[4]	9,167	[4]	8,636	[4]
Related parties									8		8		55
Segment revenues									109,922		91,412		87,274
Total revenues									100,166		82,245		78,638
Segment income from operations									3,791	[5]	5,624	[5]	4,061	[5]
Income (loss) from equity method investments									36		26		50
Depreciation and amortization									1,197	[6]	972	[6]	873	[6]
Capital expenditures and investments									2,624	[2],[7],[8]	1,256	[2],[7]	1,185	[2],[7]
Operating Segments [Member] | Refining & Marketing [Member]
Segment Reporting Information [Line Items]
Customer									85,608		67,921		65,028
Intersegment									9,294	[4]	8,782	[4]	8,301	[4]
Related parties									8		7		52
Segment revenues									94,910		76,710		73,381
Total revenues									85,616		67,928		65,080
Segment income from operations									3,206		5,098		3,591
Income (loss) from equity method investments									28		(6)		11
Depreciation and amortization									1,011		804		718
Capital expenditures and investments									2,094	[1],[2],[8]	705	[1],[2]	900	[1],[2]
Operating Segments [Member] | Refining & Marketing [Member] | Galveston Bay Refinery And Related Assets [Member]
Segment Reporting Information [Line Items]
Acquisitions									1,290
Operating Segments [Member] | Speedway [Member]
Segment Reporting Information [Line Items]
Customer									14,471		14,239		13,490
Intersegment									4	[4]	4	[4]	0	[4]
Related parties									0		0		0
Segment revenues									14,475		14,243		13,490
Total revenues									14,471		14,239		13,490
Segment income from operations									375		310		271
Income (loss) from equity method investments									0		0		0
Depreciation and amortization									112		114		110
Capital expenditures and investments									296	[2],[7],[8],[9]	340	[2],[7],[9]	164	[2],[7],[9]
Operating Segments [Member] | Pipeline Transportation [Member]
Segment Reporting Information [Line Items]
Customer									79		77		65
Intersegment									458	[4]	381	[4]	335	[4]
Related parties									0		1		3
Segment revenues									537		459		403
Total revenues									79		78		68
Segment income from operations									210	[5]	216	[5]	199	[5]
Income (loss) from equity method investments									8		32		39
Depreciation and amortization									74		54		45
Capital expenditures and investments									234	[1],[2],[8]	211	[1],[2]	121	[1],[2]
Operating Segments [Member] | Pipeline Transportation [Member] | Galveston Bay Refinery And Related Assets [Member]
Segment Reporting Information [Line Items]
Acquisitions									70
Operating Segments [Member] | Pipeline Transportation [Member] | MPLX LP [Member]
Segment Reporting Information [Line Items]
Cost of Services, Overhead									20		4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment									9,756		9,167		8,636
Intersegment Eliminations [Member] | Refining & Marketing [Member]
Segment Reporting Information [Line Items]
Intersegment									9,294		8,782		8,301
Intersegment Eliminations [Member] | Speedway [Member]
Segment Reporting Information [Line Items]
Intersegment									4		4
Intersegment Eliminations [Member] | Pipeline Transportation [Member]
Segment Reporting Information [Line Items]
Intersegment									$ 458		$ 381		$ 335

[1] Includes $1.36 billion in 2013 for the acquisition of the Galveston Bay Refinery and Related Assets, comprised of total consideration, excluding inventory and other current assets, of $1.15 billion plus assumed liabilities of $210 million. The total consideration amount of $1.15 billion includes the base purchase price and a fair-value estimate of $600 million for the contingent consideration. See Note 5 to the audited consolidated financial statements.

[2] Capital expenditures include changes in capital accruals.

[3] Includes $1.36 billion in 2013 for the acquisition of the Galveston Bay Refinery and Related Assets, comprised of total consideration, excluding inventory and other current assets, of $1.15 billion plus assumed liabilities of $210 million. The 2012 acquisitions exclude the inventory acquired and liability assumed. See Note 5.

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

[5] Included in the Pipeline Transportation segment for 2013 and 2012 are $20 million and $4 million of corporate overhead costs attributable to MPLX, which were included in items not allocated to segments prior to MPLX’s October 31, 2012 initial public offering. These expenses are not currently allocated to other segments.

[6] 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.

[7] Includes Speedway’s acquisition of convenience stores. See Note 5.

[8] The Refining & Marketing and Pipeline Transportation segments include $1.29 billion and $70 million, respectively, for the acquisition of the Galveston Bay Refinery and Related Assets. See Note 5.

[9] Includes Speedway's acquisitions of convenience stores. See Note 5 to the audited consolidated financial statements.