Supplementary Statistics - Supplementary Statistics (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Supplementary Statistics [Line Items]
Income from operations	$ 1,062		$ 301		$ 2,792		$ 2,417
Capital expenditures and investments	3,278	[1],[2],[3]	411	[1],[2],[3]	4,012	[1],[2],[3]	2,268	[1],[2],[3]
Hess' Retail Operations and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments					2,680	[3]
Galveston Bay Refinery and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments							1,360	[2],[3]
Operating Segments
Supplementary Statistics [Line Items]
Income from operations	1,159	[4]	383	[4]	3,086	[4]	2,690	[4]
Capital expenditures and investments	3,249	[3],[5]	350	[3]	3,932	[3],[5]	2,147	[3],[6]
Operating Segments | Refining & Marketing
Supplementary Statistics [Line Items]
Income from operations	971		227		2,593		2,235
Capital expenditures and investments	318	[3],[5]	243	[3]	731	[3],[5]	1,797	[2],[3],[6]
Operating Segments | Refining & Marketing | Hess' Retail Operations and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments					54	[3]
Operating Segments | Refining & Marketing | Galveston Bay Refinery and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments							1,290	[2],[3]
Operating Segments | Speedway
Supplementary Statistics [Line Items]
Income from operations	119		102		271		292
Capital expenditures and investments	2,707	[3],[5]	65	[3]	2,783	[3],[5]	177	[3]
Operating Segments | Speedway | Hess' Retail Operations and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments					2,630	[3]
Operating Segments | Pipeline Transportation
Supplementary Statistics [Line Items]
Income from operations	69	[4]	54	[4]	222	[4]	163	[4]
Capital expenditures and investments	224	[3]	42	[3]	418	[3]	173	[2],[3],[6]
Operating Segments | Pipeline Transportation | Galveston Bay Refinery and Related Assets
Supplementary Statistics [Line Items]
Capital expenditures and investments							70	[2],[3]
Corporate and Other
Supplementary Statistics [Line Items]
Income from operations	(76)	[4],[7]	(59)	[4],[7]	(204)	[4],[7],[8]	(190)	[4],[7]
Capital expenditures and investments	29	[1],[3]	61	[1],[3]	80	[1],[3]	121	[1],[3]
Capitalized interest	7		7		20		15
Segment Reconciling Items
Supplementary Statistics [Line Items]
Pension settlement expenses	$ (21)	[9]	$ (23)	[9]	$ (90)	[9]	$ (83)	[9]

[1] Includes capitalized interest of $7 million for both the three months ended September 30, 2014 and 2013, and $20 million and $15 million for the nine months ended September 30, 2014 and 2013, respectively.

[2] The nine months ended September 30, 2013 includes $1.36 billion for the acquisition of the Galveston Bay Refinery and Related Assets. See Note 4 to the unaudited consolidated financial statements.

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

[4] Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.

[5] The Speedway and Refining & Marketing segments include $2.63 billion and $54 million, respectively, for the acquisition of Hess' Retail Operations and Related Assets. See Note 4.

[6] 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 4.

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

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

[9] See Note 20.