v3.3.0.814
Equity (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 9 Months Ended
Nov. 13, 2015
Nov. 03, 2015
Oct. 20, 2015
May. 18, 2015
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Stockholders Equity Note [Line Items]                  
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest             2.00%    
Units outstanding         1,639,525   1,639,525    
Unit-based compensation awards(1) [1]             19,318    
Issuance of units under ATM program             $ 1.3    
Distributions declared (including IDRs)         $ 46.5 $ 27.9 $ 125.0 $ 79.4  
Limited Partners Common Units [Member]                  
Stockholders Equity Note [Line Items]                  
Units outstanding         80,336,711   80,336,711    
Subordinated Units [Member]                  
Stockholders Equity Note [Line Items]                  
Equity Instruments Conversion Date         Aug. 17, 2015        
Unit-based compensation awards(1)         36,951,515   0    
MPC [Member] | Limited Partners Common Units [Member]                  
Stockholders Equity Note [Line Items]                  
Units outstanding         56,932,134   56,932,134    
Subsequent Event [Member]                  
Stockholders Equity Note [Line Items]                  
Distribution Made to Limited Partner, Declaration Date     Oct. 20, 2015            
Cash distributions declared per limited partner common unit     $ 0.47            
Distributions declared (including IDRs)     $ 46.5            
Distribution Made to Limited Partner, Distribution Date Nov. 13, 2015                
Distribution Made to Limited Partner, Date of Record   Nov. 03, 2015              
ATM Program [Member]                  
Stockholders Equity Note [Line Items]                  
Equity Instrument Regulatory Filing Date       May 18, 2015          
Common Units Aggregate Value       $ 500.0          
Partners' Capital Account, Units, Sale of Units [2]             25,680    
Partners' Capital Account, Public Sale of Units Net of Offering Costs             $ 1.3    
Limited Partners Common Units [Member]                  
Stockholders Equity Note [Line Items]                  
Unit-based compensation awards(1) [1]             18,932    
Cash distributions declared per limited partner common unit         $ 0.4700 $ 0.3575 $ 1.3200 $ 1.0275  
Distributions declared (including IDRs) [3]         $ 37.7 $ 13.2 $ 74.6 $ 38.0  
Limited Partners Common Units [Member] | Subordinated Units [Member]                  
Stockholders Equity Note [Line Items]                  
Unit-based compensation awards(1)             36,951,515    
Limited Partners Common Units [Member] | MPC [Member]                  
Stockholders Equity Note [Line Items]                  
Units outstanding         57,000,000   57,000,000   20,000,000
Limited Partners Common Units [Member] | ATM Program [Member]                  
Stockholders Equity Note [Line Items]                  
Partners' Capital Account, Units, Sale of Units [2]             25,166    
General Partner Units [Member]                  
Stockholders Equity Note [Line Items]                  
Unit-based compensation awards(1) [1]             386    
Issuance of units under ATM program             $ 0.1    
General Partner Units [Member] | ATM Program [Member]                  
Stockholders Equity Note [Line Items]                  
Partners' Capital Account, Units, Sale of Units [2]             514    
Issuance of units under ATM program             $ 0.1    
[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.
[3] See Note 6 for distribution information.