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Debt - MPLX Senior Notes (Details) - MPLX LP - USD ($)
$ in Millions
3 Months Ended
Mar. 01, 2017
Mar. 31, 2017
Feb. 10, 2017
Dec. 31, 2016
Cash and Cash Equivalents        
Debt Instrument [Line Items]        
Payments to acquire business, gross $ 1,500      
Senior Notes        
Debt Instrument [Line Items]        
Net proceeds   $ 2,220    
Senior Notes | MPLX senior notes, 4.125%, due March 2027        
Debt Instrument [Line Items]        
Long-term debt, gross   $ 1,250 $ 1,250 $ 0
Debt instrument, interest rate   4.125% 4.125%  
Senior Notes | MPLX senior notes, 5.200%, due March 2047        
Debt Instrument [Line Items]        
Long-term debt, gross   $ 1,000 $ 1,000 $ 0
Debt instrument, interest rate   5.20% 5.20%