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Acquisitions and Investments - Formation of Gathering and Processing Joint Venture (Details)
bbl / d in Thousands, $ in Millions
 3 Months Ended
Jan. 01, 2017
USD ($)
bbl / d
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
 [1]
Schedule of Equity Method Investments [Line Items]      
Contribution of assets to joint venture   $ 0 $ 328
Sherwood Midstream      
Schedule of Equity Method Investments [Line Items]      
Equity method investments, ownership percentage   50.00%  
Sherwood Midstream | MPLX LP      
Schedule of Equity Method Investments [Line Items]      
Contribution of assets to joint venture $ 134    
Payments to acquire interest in joint venture 20    
Sherwood Midstream | Antero Midstream Partners L.P.      
Schedule of Equity Method Investments [Line Items]      
Payments to acquire interest in joint venture $ 154    
Ohio Fractionation      
Schedule of Equity Method Investments [Line Items]      
Capacity | bbl / d 20    
Ohio Fractionation | Sherwood Midstream      
Schedule of Equity Method Investments [Line Items]      
Payments to acquire interest in joint venture $ 126    
Sherwood Midstream Holdings      
Schedule of Equity Method Investments [Line Items]      
Equity method investments, ownership percentage   81.00%  
Ownership interest In assets sold by company in affiliate   6.00%  
Proceeds from sale of ownership interest in assets sold by company in affiliate   $ 15  
Sherwood Midstream Holdings | Direct Ownership Interest      
Schedule of Equity Method Investments [Line Items]      
Equity method investments, ownership percentage 79.00%    
Sherwood Midstream Holdings | Indirect Ownership Interest      
Schedule of Equity Method Investments [Line Items]      
Equity method investments, ownership percentage 10.50%    
Sherwood Midstream Holdings | MPLX LP      
Schedule of Equity Method Investments [Line Items]      
Contribution of assets to joint venture $ 203    
Fair value of assets contributed 209    
Gain on disposal of assets $ 2    
Sherwood Midstream Holdings | Sherwood Midstream      
Schedule of Equity Method Investments [Line Items]      
Equity method investments, ownership percentage 21.00%    
Payments to acquire interest in joint venture $ 44    
[1] MarkWest’s contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. See Note 5.