v3.3.0.814
Equity - Changes in Partners Capital, Unit Rollforward (Details) - shares
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2015
Stockholders Equity [Line Items]    
Balance at December 31, 2014   81,931,238
Units converted [1]   19,318
Balance at September 30, 2015 81,976,236 81,976,236
Limited Partners Common Units [Member]    
Stockholders Equity [Line Items]    
Balance at December 31, 2014   43,341,098
Units converted [1]   18,932
Balance at September 30, 2015 80,336,711 80,336,711
Limited Partners Subordinated Units [Member]    
Stockholders Equity [Line Items]    
Balance at December 31, 2014   36,951,515
Balance at September 30, 2015 0 0
General Partner Units [Member]    
Stockholders Equity [Line Items]    
Balance at December 31, 2014   1,638,625
Units converted [1]   386
Balance at September 30, 2015 1,639,525 1,639,525
ATM Program [Member]    
Stockholders Equity [Line Items]    
Issuance of units under the ATM Program(2) [2]   25,680
ATM Program [Member] | Limited Partners Common Units [Member]    
Stockholders Equity [Line Items]    
Issuance of units under the ATM Program(2) [2]   25,166
ATM Program [Member] | General Partner Units [Member]    
Stockholders Equity [Line Items]    
Issuance of units under the ATM Program(2) [2]   514
Subordinated Units [Member]    
Stockholders Equity [Line Items]    
Units converted 36,951,515 0
Subordinated Units [Member] | Limited Partners Common Units [Member]    
Stockholders Equity [Line Items]    
Units converted   36,951,515
Subordinated Units [Member] | Limited Partners Subordinated Units [Member]    
Stockholders Equity [Line Items]    
Units converted   (36,951,515)
[1] As a result of the unit-based compensation awards issued during the period, MPLX GP contributed less than $0.1 million in exchange for 386 general partner units to maintain its two percent general partner interest.
[2] As a result of common units issued under the ATM Program during the period, MPLX GP contributed less than $0.1 million in exchange for 514 general partner units to maintain its two percent general partner interest.