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Related Party Agreements and Transactions - Payables to Related Parties (Detail) - USD ($)
$ in Millions
Jun. 30, 2017
Dec. 31, 2016
Related Party Transaction [Line Items]    
Payables - related parties $ 93 $ 87
MPC    
Related Party Transaction [Line Items]    
Payables - related parties 74 63
MarkWest Utica EMG [Member]    
Related Party Transaction [Line Items]    
Payables - related parties 15 $ 24
Other [Member]    
Related Party Transaction [Line Items]    
Payables - related parties $ 4