Supplementary Statistics - Supplementary Statistics (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended					3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Mar. 31, 2013 Galveston Bay Refinery and Related Assets	Jun. 30, 2014 Operating Segments		Jun. 30, 2013 Operating Segments		Jun. 30, 2014 Operating Segments		Jun. 30, 2013 Operating Segments		Jun. 30, 2014 Operating Segments Refining & Marketing		Jun. 30, 2013 Operating Segments Refining & Marketing		Jun. 30, 2014 Operating Segments Refining & Marketing		Jun. 30, 2013 Operating Segments Refining & Marketing		Jun. 30, 2014 Operating Segments Speedway		Jun. 30, 2013 Operating Segments Speedway		Jun. 30, 2014 Operating Segments Speedway		Jun. 30, 2013 Operating Segments Speedway		Jun. 30, 2014 Operating Segments Pipeline Transportation		Jun. 30, 2013 Operating Segments Pipeline Transportation		Jun. 30, 2014 Operating Segments Pipeline Transportation		Jun. 30, 2013 Operating Segments Pipeline Transportation		Jun. 30, 2014 Corporate and Other		Jun. 30, 2013 Corporate and Other		Jun. 30, 2014 Corporate and Other		Jun. 30, 2013 Corporate and Other		Jun. 30, 2014 Segment Reconciling Items		Jun. 30, 2013 Segment Reconciling Items		Jun. 30, 2014 Segment Reconciling Items		Jun. 30, 2013 Segment Reconciling Items
Supplementary Statistics [Line Items]
Income from operations	$ 1,369		$ 960		$ 1,730		$ 2,116			$ 1,435	[1]	$ 1,084	[1]	$ 1,927	[1]	$ 2,307	[1]	$ 1,260		$ 903		$ 1,622		$ 2,008		$ 94		$ 123		$ 152		$ 190		$ 81	[1]	$ 58	[1]	$ 153	[1]	$ 109	[1]	$ (61)	[1],[2]	$ (64)	[1],[2]	$ (128)	[1],[3]	$ (131)	[1],[2]
Pension settlement expenses																																																		(5)	[4]	(60)	[4]	(69)	[4]	(60)	[4]
Capital expenditures and investments	363	[5],[6],[7]	283	[5],[6],[7]	734	[5],[6]	1,857	[5],[6]		343	[6]	251	[6]	683	[6]	1,797	[6],[8]	235	[6]	134	[6],[8]	413	[6]	1,554	[6],[8]	44	[6]	76	[6]	76	[6]	112	[6]	64	[6]	41	[6],[8]	194	[6]	131	[6],[8]	20	[6],[7]	32	[6],[7]	51	[5],[6]	60	[5],[6]
Fair value of contingent consideration as of acquisition date									600
Capitalized interest																																										$ 7		$ 4		$ 13		$ 8

[1] 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.

[2] Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets.

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

[4] See Note 18.

[5] 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.

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

[7] 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.

[8] The Refining & Marketing and Pipeline Transportation segments include the acquisition of the Galveston Bay Refinery and Related Assets. See Note 4.