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Income Tax (Reconciliation of Federal Statutory Income Tax Rate) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Entity Information [Line Items] |  |  |  |
(Loss) income before (benefit) provision for income tax |  | $ 1,842 | $ 837 | $ 422
Federal statutory rate | [1] |  |  | 35.00%
Federal income tax at statutory rate |  |  |  | $ (14)
State income taxes net of federal benefit |  |  |  | (1)
Provision on income from MPLX LP Class A units |  |  |  | 3
Change in state statutory rate |  |  |  | (1)
Other |  |  |  | 1
Provision/(benefit) for income taxes |  | $ 8 | $ 1 | (12)
Reportable Legal Entities [Member] | MarkWest Hydrocarbon [Member] |  |  |  |
Entity Information [Line Items] |  |  |  |
(Loss) income before (benefit) provision for income tax | [1] |  |  | (41)
Federal income tax at statutory rate | [1] |  |  | (14)
State income taxes net of federal benefit | [1] |  |  | (2)
Provision on income from MPLX LP Class A units | [1] |  |  | 3
Change in state statutory rate | [1] |  |  | (1)
Other | [1] |  |  | 1
Provision/(benefit) for income taxes | [1] |  |  | (13)
Reportable Legal Entities [Member] | Partnership [Member] |  |  |  |
Entity Information [Line Items] |  |  |  |
(Loss) income before (benefit) provision for income tax |  |  |  | 461
Federal income tax at statutory rate |  |  |  | 0
State income taxes net of federal benefit |  |  |  | 1
Provision on income from MPLX LP Class A units |  |  |  | 0
Change in state statutory rate |  |  |  | 0
Other |  |  |  | 0
Provision/(benefit) for income taxes |  |  |  | 1
Consolidation, Eliminations [Member] |  |  |  |
Entity Information [Line Items] |  |  |  |
(Loss) income before (benefit) provision for income tax |  |  |  | 2
Federal income tax at statutory rate |  |  |  | 0
State income taxes net of federal benefit |  |  |  | 0
Provision on income from MPLX LP Class A units |  |  |  | 0
Change in state statutory rate |  |  |  | 0
Other |  |  |  | 0
Provision/(benefit) for income taxes |  |  |  | $ 0
[1] | MarkWest Hydrocarbon paid tax on its share of MPLX’s income or loss as a result of its ownership of MPLX LP Class A units through September 1, 2016.

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- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(10)) -URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(8)) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(15)) -URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260 + Details
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