Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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 borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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- Definition

The cash inflow from borrowing by issuing commercial paper.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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The cash outflow due to repaying amounts borrowed by issuing commercial paper.

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The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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Debt - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Debt - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Commercial paper – issued	$ 300	$ 264
Commercial paper - repayments	300	$ 76
Commercial paper	0		$ 0
Bank revolving credit facility \| Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	0
Bank revolving credit facility \| Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	0		0
Trade receivables securitization facility due July 2019
Debt Instrument [Line Items]
Long-term debt, gross	0
Proceeds from Long-term Lines of Credit	0
Repayments of Long-term Lines of Credit	0
MPLX bank revolving credit facility due 2020 \| MPLX LP
Debt Instrument [Line Items]
Remaining borrowing capacity	2,000
MPLX bank revolving credit facility due 2020 \| MPLX LP \| Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	3
MPLX bank revolving credit facility due 2020 \| MPLX LP \| Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 0		$ 0