Debt (Available Capacity under our Facilities) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Jul. 31, 2022	Jul. 07, 2022	Dec. 31, 2021
MPLX
Line of Credit Facility [Line Items]
Outstanding Borrowings	$ 0			$ 300
MPC bank revolving credit facility due July 2027
Line of Credit Facility [Line Items]
Total Capacity	5,000
Outstanding Borrowings	0
Outstanding Letters of Credit	1
Available Capacity	$ 4,999
Weighted Average Interest Rate	0.00%
Trade Receivables Securitization due September 2023
Line of Credit Facility [Line Items]
Total Capacity	$ 100
Outstanding Borrowings	0
Outstanding Letters of Credit	100
Available Capacity	$ 0
Weighted Average Interest Rate	0.00%
Line of credit facility, maximum borrowing capacity		$ 100
MPLX revolving credit facility due July 2027 | MPLX
Line of Credit Facility [Line Items]
Total Capacity	$ 2,000
Outstanding Borrowings	0
Outstanding Letters of Credit	0
Available Capacity	$ 2,000
Weighted Average Interest Rate	0.00%
Line of credit facility, maximum borrowing capacity			$ 2,000
Trade Receivables Securitization due September 2023
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 100
Trade Receivables Securitization due September 2023 | Purchase crude oil from Strategic Petroleum Reserve
Line of Credit Facility [Line Items]
Outstanding Letters of Credit	$ 1,050