Subsequent Events (Detail) (USD $)	1 Months Ended				1 Months Ended				1 Months Ended
	Feb. 01, 2012	Feb. 03, 2012	Oct. 31, 2012 Affiliate Initial Public Offering [Member] Limited Partner [Member]	Nov. 05, 2012 Repurchase of Equity [Member] November 2012 ASR Program [Member]	Nov. 05, 2012 Repurchase of Equity [Member] February and November 2012 ASR Programs [Member] Plans	Oct. 31, 2012 MPLX [Member] Affiliate Initial Public Offering [Member]	Oct. 31, 2012 MPLX [Member] Affiliate Initial Public Offering [Member] Midwest And Gulf Coast [Member]	Oct. 31, 2012 MPLX [Member] Affiliate Initial Public Offering [Member] West Virginia [Member]	Oct. 31, 2012 MPLX [Member] Affiliate Initial Public Offering [Member] Public Offering Closed [Member]	Oct. 31, 2012 MPLX [Member] Affiliate Initial Public Offering [Member] Underwriters [Member]	Oct. 31, 2012 Pipe Line Holdings [Member] Affiliate Initial Public Offering [Member]	Oct. 07, 2012 BP [Member] Business Combination [Member] Pipeline site Terminal MW BPD	Oct. 07, 2012 BP [Member] Business Combination [Member] Contingent Earnout [Member]
Subsequent Event [Line Items]
Refinery capacity, barrel-per-day												451,000
Intrastate natural gas liquid pipelines												3
Number of branded sites (in number of sites)												1,200
Electric cogeneration capacity, megawatts												1,040
Base purchase price												$ 598,000,000
Inventories at current price												1,200,000,000
Contingent earnout													700,000,000
Term of payment of maximum earnout provision payable to the company, years													6 years
Number of light product terminals (in number of terminals)												4
Initial public offering of common units (in number of common units)									19,895,000	2,595,000
Price of common unit (in USD per common unit)						$ 22.00
Net proceeds to MPLX from the sale of the units						405,000,000
Payment of financing costs						2,000,000
Offering Costs						31,000,000
Contribution made by MPLX to Pipe Line Holdings						(192,000,000)					192,000,000
Net proceeds distributed by MPLX to MPC						203,000,000
MPC's partnership interest in MPLX (in percentage)			73.60%
Company's ownership percentage represented by the sale of units in MPLX's initial public offering (in percentage)						26.40%
MPC's partnership interest in assets (in percentage)							51.00%	100.00%
Repurchase shares of MPC common stock under ASR program		850,000,000		500,000,000	1,350,000,000
Stock repurchase plan authorized amount	2,000,000,000
Number of Accelerated Share Repurchase Programs					2
Total authorized amount available for share repurchase					$ 650,000,000