v3.26.1
Credit Agreement (Detail) - USD ($)
$ in Millions
Jun. 30, 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
Letters of Credit Outstanding, Amount 1  
Line of Credit Facility, Remaining Borrowing Capacity 2,500  
MPLX Revolving Credit Facility due April 2031    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity 2,500  
MPLX Revolving Credit Facility due April 2031 | Letter of Credit    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity 150  
MPLX Revolving Credit Facility due April 2031 | Swing-line Loan    
Debt Instrument [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 150