Line of Credit Facility, Remaining Borrowing Capacity, Percentage

No definition available.

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- Definition

Percent of Par

+ References

No definition available.

+ Details

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net cash inflow or outflow in aggregate debt due to repayments and proceeds from additional borrowings.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Debt - Additional Information (Detail) - MPLX LP - USD ($) $ in Millions				3 Months Ended
	Feb. 08, 2018	Jul. 21, 2017	Oct. 27, 2015	Mar. 31, 2018	Jan. 02, 2018	Dec. 31, 2017	Feb. 10, 2017	Dec. 31, 2016
MPLX Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity								$ 2,000
Debt Instrument, Term			5 years
Bank revolving credit facility due 2022
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 2,250
Debt Instrument, Term		5 years
Proceeds from Lines of Credit				$ 50
Debt Instrument, Interest Rate, Effective Percentage				2.975%
Letters of Credit Outstanding				$ 3
Line of Credit Facility, Remaining Borrowing Capacity				$ 2,247
Line of Credit Facility, Remaining Borrowing Capacity, Percentage				99.90%
MPLX 364-Day Term Loan [Member]
Debt Instrument [Line Items]
Current borrowing capacity					$ 4,100
Repayments of Short-term Debt	$ 4,100
Line of Credit [Member] \| Bank revolving credit facility due 2022
Debt Instrument [Line Items]
Long-term debt, gross				$ 0		$ 505
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 5,500
Debt Instrument, Face Amount							$ 2,250
Proceeds from new debt				2,220
Senior Notes [Member] \| Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 500		0
Debt Instrument, Interest Rate, Stated Percentage				3.375%
Percent of Par	99.931%
Senior Notes [Member] \| 4.125% senior notes due March 2027
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,250		1,250	$ 1,250
Debt Instrument, Interest Rate, Stated Percentage				4.125%			4.125%
Senior Notes [Member] \| 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,000		1,000	$ 1,000
Debt Instrument, Interest Rate, Stated Percentage				5.20%			5.20%
Senior Notes [Member] \| Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,250		0
Debt Instrument, Interest Rate, Stated Percentage				4.00%
Percent of Par	99.551%
Senior Notes [Member] \| Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,750		0
Debt Instrument, Interest Rate, Stated Percentage				4.50%
Percent of Par	98.811%
Senior Notes [Member] \| Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,500		0
Debt Instrument, Interest Rate, Stated Percentage				4.70%
Percent of Par	99.348%
Senior Notes [Member] \| Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 500		$ 0
Debt Instrument, Interest Rate, Stated Percentage				4.90%
Percent of Par	99.289%