Debt (Outstanding Borrowings) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Total	$ 3,395		$ 3,355
Unamortized discount	(10)		(10)
Fair value adjustments	11	[1]	16	[1]
Long-term debt due within one year	(23)		(19)
Total long-term debt due after one year	3,373		3,342
MPC Revolver [Member]
Debt Instrument [Line Items]
Borrowings outstanding at period end	0		0
Consolidated Subsidiaries [Member] | Trade Receivables Securitization [Member]
Debt Instrument [Line Items]
Trade receivables securitization facility due 2016	0		0
MPLX Operations LLC [Member] | MPLX Revolver [Member]
Debt Instrument [Line Items]
Borrowings outstanding at period end	0		0
Senior Notes [Member] | 3.500% Senior Notes Due March 1, 2016 [Member]
Debt Instrument [Line Items]
Senior notes	750		750
Debt instrument, interest rate	3.50%
Debt instrument, maturity date	Mar. 01, 2016
Senior Notes [Member] | 5.125% Senior Notes Due March 1, 2021 [Member]
Debt Instrument [Line Items]
Senior notes	1,000		1,000
Debt instrument, interest rate	5.125%
Debt instrument, maturity date	Mar. 01, 2021
Senior Notes [Member] | 6.500% Senior Notes Due March 1, 2041 [Member]
Debt Instrument [Line Items]
Senior notes	1,250		1,250
Debt instrument, interest rate	6.50%
Debt instrument, maturity date	Mar. 01, 2041
Capital Lease Obligations [Member] | Consolidated Subsidiaries [Member]
Debt Instrument [Line Items]
Capital lease obligations due 2014-2028	$ 395		$ 355
Trade Receivables Securitization [Member] | Consolidated Subsidiaries [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Dec. 31, 2014
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Sep. 14, 2017
Revolving Credit Facility [Member] | MPLX Operations LLC [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Oct. 31, 2017

[1] See Notes 17 and 18 for information on interest rate swaps.