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Derivative Financial Instruments (Derivatives Income Statement Location) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized gains/(losses) | [1] | $ 5 | $ (6) | $ (36)
Total derivative loss |  | (3) | (24) | (42)
Product sales |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Realized gains/(losses) |  | 4 | (9) | 2
Unrealized gains/(losses) |  | 2 | 4 | (15)
Total derivative loss |  | 6 | (5) | (13)
Purchased product costs |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Realized gains/(losses) |  | (12) | (9) | (5)
Unrealized gains/(losses) |  | 3 | (10) | (22)
Total derivative loss |  | (9) | (19) | (27)
Cost of revenues |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Realized gains/(losses) |  | 0 | 0 | (3)
Unrealized gains/(losses) |  | 0 | 0 | 1
Total derivative loss |  | $ 0 | $ 0 | $ (2)
[1] | MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

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- Definition Amount of realized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References No definition available. + Details
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- Definition Amount of unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References No definition available. + Details
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- 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
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- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4CC -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959 + Details
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