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Related Party Agreements and Transactions (Summary of Employee Services Expenses by Income Statement Line Item) (Detail) - MPC - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Related Party Transaction [Line Items] |  |  |
Expenses incurred under employee services agreements | $ 640 | $ 487 | $ 449
Rental cost of sales - related parties [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Expenses incurred under employee services agreements | 3 | 1 | 0
Purchases - related parties |  |  |
Related Party Transaction [Line Items] |  |  |
Expenses incurred under employee services agreements | 528 | 385 | 349
General and Administrative Expense - Related Party [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Expenses incurred under employee services agreements | $ 109 | $ 101 |
General and administrative expenses |  |  |
Related Party Transaction [Line Items] |  |  |
Expenses incurred under employee services agreements |  |  | $ 100

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- Definition Amount of expense for salary, wage, profit sharing; incentive and equity-based compensation; and other employee benefit. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(b)(4)) -URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227 + 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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- Details
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