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Acquisitions Acquisition of HST, WHC & MPLXT (Details)
bbl in Millions, $ in Millions
6 Months Ended
Mar. 01, 2017
USD ($)
mi
shares
bbl
Mar. 31, 2016
USD ($)
Jun. 30, 2017
USD ($)
shares
Business Acquisition [Line Items]      
Contribution from MPC | $     $ 12
Number of natural gas liquids storage caverns 9    
Number of light product terminals 62    
HST & WHC & MPLXT [Member]      
Business Acquisition [Line Items]      
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned | $ $ 504    
Business Acquisition, Equity Interest Issued or Issuable, Fair Value Assigned | $ 503    
Partners' Capital Account, Units, Acquisitions | shares [1]     13,224,873
HST & WHC & MPLXT [Member] | Cash and Cash Equivalents [Member]      
Business Acquisition [Line Items]      
Payments to Acquire Businesses, Gross | $ $ 1,500    
HST & WHC & MPLXT [Member] | General Partner Units [Member]      
Business Acquisition [Line Items]      
Partners' Capital Account, Units, Acquisitions | shares [1] 264,497   264,497
HST & WHC & MPLXT [Member] | Limited Partners Common Units [Member]      
Business Acquisition [Line Items]      
Partners' Capital Account, Units, Acquisitions | shares [1]     12,960,376
HST & WHC & MPLXT [Member] | General Partner Common Units [Member]      
Business Acquisition [Line Items]      
Partners' Capital Account, Units, Acquisitions | shares [1] 9,197,900    
MPLX Logistics LLC [Member] | HST & WHC & MPLXT [Member] | Limited Partners Common Units [Member]      
Business Acquisition [Line Items]      
Partners' Capital Account, Units, Acquisitions | shares [1] 2,630,427    
MPLX Holdings Inc [Member] | HST & WHC & MPLXT [Member] | Limited Partners Common Units [Member]      
Business Acquisition [Line Items]      
Partners' Capital Account, Units, Acquisitions | shares [1] 1,132,049    
Natural gas liquids storage caverns [Member]      
Business Acquisition [Line Items]      
Storage Capacity | bbl 1.8    
Light-product terminal [Member]      
Business Acquisition [Line Items]      
Storage Capacity | bbl 23.6    
Refined Products [Member]      
Business Acquisition [Line Items]      
Miles of pipeline | mi 430    
Crude Oil [Member]      
Business Acquisition [Line Items]      
Miles of pipeline | mi 174    
Wholly Owned Properties [Member]      
Business Acquisition [Line Items]      
Number of light product terminals 59    
Property Subject to Operating Lease [Member]      
Business Acquisition [Line Items]      
Number of light product terminals 1    
Partially Owned Properties [Member]      
Business Acquisition [Line Items]      
Number of light product terminals 2    
MPC      
Business Acquisition [Line Items]      
Contribution from MPC | $ $ 6 $ 15  
MPC | Limited Partners Common Units [Member]      
Business Acquisition [Line Items]      
Contribution from MPC | $     $ 0
[1] See Note 3 for information regarding the HST, WHC and MPLXT acquisition.