Debt - Summary of Outstanding Borrowings (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Feb. 18, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
MPLX Credit Agreement	$ 0		$ 0
Finance lease obligations	8		6
Debt and Lease Obligation	22,708		21,206
Unamortized debt issuance costs	(143)		(126)
Unamortized discount	(147)		(132)
Amounts due within one year	2,697		1,693
Total long-term debt due after one year	19,721		19,255
Senior Notes Due February 2025 \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.00%
MPLX LP [Member]
Debt Instrument [Line Items]
Senior Notes	22,658		21,158
MarkWest [Member]
Debt Instrument [Line Items]
Senior Notes	11		11
ANDX LP [Member]
Debt Instrument [Line Items]
Senior Notes	$ 31		$ 31

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

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Amount, after accumulated amortization, of debt discount.

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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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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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