v3.26.1
Credit Agreement (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Apr. 07, 2026
Debt Instrument [Line Items]    
Line of Credit Facility, Remaining Borrowing Capacity, Percentage 100.00%  
MPLX Revolving Credit Facility due June 2027    
Debt Instrument [Line Items]    
Long-term Line of Credit $ 0  
Line of Credit Facility, Maximum Borrowing Capacity $ 2,000  
Debt Instrument, Description of Variable Rate Basis Adjusted Term SOFR or the Alternate Base Rate, both as defined in the MPLX Credit Agreement, plus an applicable margin.  
Letters of Credit Outstanding, Amount $ 1  
Line of Credit Facility, Remaining Borrowing Capacity 2,000  
MPLX Revolving Credit Facility due June 2027 | Letter of Credit    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 150  
MPLX Revolving Credit Facility due April 2031 | Subsequent Event    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity   $ 2,500
MPLX Revolving Credit Facility due April 2031 | Letter of Credit | Subsequent Event    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity   150
MPLX Revolving Credit Facility due April 2031 | Swing-line Loan | Subsequent Event    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity   $ 150