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Debt - Summary of Outstanding Borrowings (Detail) - USD ($) $ in Millions | Jun. 30, 2017 | Feb. 10, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Total | $ 7,108 |  | $ 4,858
Unamortized debt issuance costs | (28) |  | (7)
Unamortized discount | (413) |  | (428)
Amounts due within one year | (1) |  | (1)
Total long-term debt due after one year | 6,666 |  | 4,422
Capital Lease Obligations [Member] | Marathon Pipe Line Llc [Member] |  |  |
Debt Instrument [Line Items] |  |  |
MPL - capital lease obligations due 2020 | 8 |  | 8
Bank revolving credit facility due 2020 | Line of Credit [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 0 |  | 0
Term loan facility due 2019 | Unsecured Debt [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 250 |  | 250
5.500% senior notes due February 2023 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 710 |  | 710
4.500% senior notes due July 2023 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 989 |  | 989
4.875% senior notes due December 2024 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 1,149 |  | 1,149
4.000% senior notes due February 2025 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 500 |  | 500
4.875% senior notes due June 2025 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 1,189 |  | 1,189
4.125% senior notes due 2027 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 1,250 | $ 1,250 | 0
5.200% senior notes due 2047 | Senior Notes [Member] | Mplx Lp [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | 1,000 | $ 1,000 | 0
MarkWest - 4.500% - 5.500% senior notes, due 2023-2025 | Senior Notes [Member] | MarkWest [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, gross | $ 63 |  | $ 63

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- Definition Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737 Reference 2: 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 3: 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(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13,16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 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 + 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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