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Debt (MPLX Bank Revolving Credit Facility) (Details) - MPLX LP: - USD ($)
$ in Millions
Jul. 07, 2022
Jun. 30, 2022
MPLX bank revolving credit facility due July 2024    
Line of Credit Facility [Line Items]    
Maximum borrowing capacity   $ 3,500
MPLX bank revolving credit facility due July 2027 | Subsequent Event    
Line of Credit Facility [Line Items]    
Maximum borrowing capacity $ 2,000  
Description of variable rate basis at either the Adjusted Term SOFR or the Alternate Base Rate, both as defined in the MPLX Credit Agreement, plus an applicable margin  
MPLX bank revolving credit facility due July 2027 | Letter of Credit | Subsequent Event    
Line of Credit Facility [Line Items]    
Maximum borrowing capacity $ 150