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MPLX LP - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
1 Months Ended 8 Months Ended 1 Months Ended 6 Months Ended
Jun. 30, 2013
MPLX LP [Member]
Noncontrolling Interests [Member]
Oct. 31, 2012
MPLX LP [Member]
IPO [Member]
Jun. 30, 2013
MPLX LP [Member]
General Partner [Member]
Jun. 30, 2013
MPLX LP [Member]
General Partner and Limited Partner [Member]
Jun. 30, 2013
Butane Cavern [Member]
MPLX LP [Member]
May 01, 2013
MPLX Pipe Line Holdings LP [Member]
May 01, 2013
MPLX Pipe Line Holdings LP [Member]
MPLX LP [Member]
Apr. 30, 2013
MPLX Pipe Line Holdings LP [Member]
MPLX LP [Member]
General Partner [Member]
Noncontrolling Interest [Line Items]                
Ownership Percentage         100.00% 44.00% 56.00% 51.00%
Sale of additional ownership interest percentage           5.00%    
Proceeds from sale of ownership interest           $ 100    
Initial public offering of common units (in number of common units)   19,895,000            
Initial public offering date of MPLX LP   October 31, 2012            
Net proceeds to MPLX from the sale of the units   $ 407            
MPC's partnership interest in MPLX (in percentage)     2.00% 73.60%        
Public ownership interest percentage in MPLX 26.40%