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Related Party Agreements and Transactions - Receivables from Related Parties (Detail) - USD ($)
$ in Millions
Jun. 30, 2017
Dec. 31, 2016
Related Party Transaction [Line Items]    
Receivables - related parties $ 173 $ 247
MPC    
Related Party Transaction [Line Items]    
Receivables - related parties 167 242
MarkWest Utica EMG [Member]    
Related Party Transaction [Line Items]    
Receivables - related parties 1 2
Ohio Gathering Company, LLC [Member]    
Related Party Transaction [Line Items]    
Receivables - related parties 2 2
Other [Member]    
Related Party Transaction [Line Items]    
Receivables - related parties $ 3 $ 1