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Related Party Agreements and Transaction - Summary of Charges for Omnibus Agreement (Detail) - MPC - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Related Party Transaction [Line Items]        
Charges for services under an omnibus agreement $ 29 $ 23 $ 52 $ 40
Purchases - related parties [Member]        
Related Party Transaction [Line Items]        
Charges for services under an omnibus agreement 18 11 33 18
General and administrative expenses [Member]        
Related Party Transaction [Line Items]        
Charges for services under an omnibus agreement $ 11 $ 12 $ 19 $ 22