Debt (Outstanding Borrowings) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total finance lease liabilities	$ 530	$ 598
Total debt	27,080	25,948
Unamortized debt issuance costs	(142)	(129)
Unamortized discount, net of unamortized premium	(238)	(280)
Amounts due within one year	(1,066)	(571)
Total long-term debt due after one year	25,634	24,968
Marathon Petroleum Corporation
Debt Instrument [Line Items]
Notes payable	1	1
Total debt	6,972	7,039
Marathon Petroleum Corporation \| Senior Notes
Debt Instrument [Line Items]
Long-term debt outstanding	6,449	6,449
Marathon Petroleum Corporation \| Finance Lease
Debt Instrument [Line Items]
Total finance lease liabilities	522	589
MPLX
Debt Instrument [Line Items]
Bank revolving credit facility	0	300
Total debt	20,108	18,909
MPLX \| Senior Notes
Debt Instrument [Line Items]
Long-term debt outstanding	20,100	18,600
MPLX \| Finance Lease
Debt Instrument [Line Items]
Total finance lease liabilities	$ 8	$ 9

Amount of short-term and long-term debt and lease obligation.

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Amount of debt and lease obligation, classified as current.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount (premium).

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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