Segment Information - Reconciliation Of Segment Income From Operations To Income Before Income Taxes (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, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	$ 1,369		$ 960		$ 1,730		$ 2,116
Net interest and other financial income (costs)	(48)		(45)		(94)		(93)
Income before income taxes	1,321		915		1,636		2,023
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	1,435	[1]	1,084	[1]	1,927	[1]	2,307	[1]
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	(61)	[1],[2]	(64)	[1],[2]	(128)	[1],[3]	(131)	[1],[2]
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pension settlement expenses	$ (5)	[4]	$ (60)	[4]	$ (69)	[4]	$ (60)	[4]

[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.