Segment Information - Income From Operations Attributable To Operating Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ (26,844)		$ (25,677)		$ (50,129)		$ (49,007)
Income from operations	1,369		960		1,730		2,116
Income (loss) from equity method investments	57		7		92		7
Depreciation and amortization	325		302		645		589
Capital expenditures and investments	363	[1],[2],[3]	283	[1],[2],[3]	734	[1],[2]	1,857	[1],[2]
Refining & Marketing
Segment Reporting Information [Line Items]
Revenues	(22,917)		(21,890)		(42,727)		(41,764)
Speedway
Segment Reporting Information [Line Items]
Revenues	(3,908)		(3,768)		(7,366)		(7,209)
Pipeline Transportation
Segment Reporting Information [Line Items]
Revenues	(19)		(19)		(36)		(40)
Reportable Segment
Segment Reporting Information [Line Items]
Revenues	(26,844)		(25,677)		(50,129)		(49,013)
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	2,722	[4]	2,554	[4]	5,085	[4]	4,858	[4]
Intersegment Eliminations | Refining & Marketing
Segment Reporting Information [Line Items]
Revenues	2,590	[4]	2,434	[4]	4,823	[4]	4,633	[4]
Intersegment Eliminations | Speedway
Segment Reporting Information [Line Items]
Revenues	1	[4]	1	[4]	2	[4]	2	[4]
Intersegment Eliminations | Pipeline Transportation
Segment Reporting Information [Line Items]
Revenues	131	[4]	119	[4]	260	[4]	223	[4]
Operating Segments
Segment Reporting Information [Line Items]
Revenues	(29,566)		(28,231)		(55,214)		(53,871)
Income from operations	1,435	[5]	1,084	[5]	1,927	[5]	2,307	[5]
Income (loss) from equity method investments	57		7		92		7
Depreciation and amortization	312	[6]	297	[6]	620	[6]	578	[6]
Capital expenditures and investments	343	[2]	251	[2]	683	[2]	1,797	[2],[7]
Operating Segments | Refining & Marketing
Segment Reporting Information [Line Items]
Revenues	(25,507)		(24,324)		(47,550)		(46,397)
Income from operations	1,260		903		1,622		2,008
Income (loss) from equity method investments	35		3		59		(1)
Depreciation and amortization	264	[6]	252	[6]	525	[6]	488	[6]
Capital expenditures and investments	235	[2]	134	[2],[7]	413	[2]	1,554	[2],[7]
Operating Segments | Speedway
Segment Reporting Information [Line Items]
Revenues	(3,909)		(3,769)		(7,368)		(7,211)
Income from operations	94		123		152		190
Income (loss) from equity method investments	0		0		0		0
Depreciation and amortization	29	[6]	27	[6]	57	[6]	54	[6]
Capital expenditures and investments	44	[2]	76	[2]	76	[2]	112	[2]
Operating Segments | Pipeline Transportation
Segment Reporting Information [Line Items]
Revenues	(150)		(138)		(296)		(263)
Income from operations	81	[5]	58	[5]	153	[5]	109	[5]
Income (loss) from equity method investments	22		4		33		8
Depreciation and amortization	19	[6]	18	[6]	38	[6]	36	[6]
Capital expenditures and investments	$ 64	[2]	$ 41	[2],[7]	$ 194	[2]	$ 131	[2],[7]

[1] The six months ended June 30, 2013 includes the acquisition of the Galveston Bay Refinery and Related Assets, comprised of total consideration, excluding inventory and other current assets, plus assumed liabilities. Total consideration includes the base purchase price and a fair-value estimate of $600 million for the contingent consideration. See Note 4 to the unaudited consolidated financial statements.

[2] Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.

[3] Includes capitalized interest $7 million and $4 million for the three months ended June 30, 2014 and 2013, respectively, and $13 million and $8 million for the six months ended June 30, 2014 and 2013, respectively.

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

[5] Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. These expenses are not allocated to the Refining & Marketing and Speedway 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] The Refining & Marketing and Pipeline Transportation segments include the acquisition of the Galveston Bay Refinery and Related Assets. See Note 4.