<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Version>2.4.1.9</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>246</ContextCount>
  <ElementCount>300</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>80</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>11</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/StatementCondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/StatementCondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Condensed Consolidated Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/StatementCondensedConsolidatedStatementsOfOperations</Role>
      <ShortName>Condensed Consolidated Statements of Operations</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Condensed Consolidated Statements of Changes in Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/StatementCondensedConsolidatedStatementsOfChangesInEquity</Role>
      <ShortName>Condensed Consolidated Statements of Changes in Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/StatementCondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Organization and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureOrganizationAndBasisOfPresentation</Role>
      <ShortName>Organization and Basis of Presentation</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Recent Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureRecentAccountingPronouncements</Role>
      <ShortName>Recent Accounting Pronouncements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Variable Interest Entities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureVariableInterestEntities</Role>
      <ShortName>Variable Interest Entities</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Other Equity Interests</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureOtherEquityInterests</Role>
      <ShortName>Other Equity Interests</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureDerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValue</Role>
      <ShortName>Fair Value</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureInventories</Role>
      <ShortName>Inventories</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Impairment of Long-Lived Assets and Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureImpairmentOfLongLivedAssetsAndGoodwill</Role>
      <ShortName>Impairment of Long-Lived Assets and Goodwill</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureLongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEquity</Role>
      <ShortName>Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Earnings Per Common Unit</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEarningsPerCommonUnit</Role>
      <ShortName>Earnings Per Common Unit</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Supplemental Condensed Consolidating Financial Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCondensedConsolidatingFinancialInformation</Role>
      <ShortName>Supplemental Condensed Consolidating Financial Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Supplemental Cash Flow Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCashFlowInformation</Role>
      <ShortName>Supplemental Cash Flow Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureDerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValueTables</Role>
      <ShortName>Fair Value (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureInventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Long-Term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureLongTermDebtTables</Role>
      <ShortName>Long-Term Debt (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEquityTables</Role>
      <ShortName>Equity (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Income Tax (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureIncomeTaxTables</Role>
      <ShortName>Income Tax (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>31303 - Disclosure - Earnings Per Common Unit (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEarningsPerCommonUnitTables</Role>
      <ShortName>Earnings Per Common Unit (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Supplemental Condensed Consolidating Financial Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCondensedConsolidatingFinancialInformationTables</Role>
      <ShortName>Supplemental Condensed Consolidating Financial Information (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>31603 - Disclosure - Supplemental Cash Flow Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCashFlowInformationTables</Role>
      <ShortName>Supplemental Cash Flow Information (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Variable Interest Entity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureVariableInterestEntityDetails</Role>
      <ShortName>Variable Interest Entity (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Other Equity Interests (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureOtherEquityInterestsDetails</Role>
      <ShortName>Other Equity Interests (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureDerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>40502 - Disclosure - Derivative Financial Instruments (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureDerivativeFinancialInstrumentsDetails2</Role>
      <ShortName>Derivative Financial Instruments (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>40503 - Disclosure - Derivative Financial Instruments (Details 3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureDerivativeFinancialInstrumentsDetails3</Role>
      <ShortName>Derivative Financial Instruments (Details 3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValueDetails</Role>
      <ShortName>Fair Value (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Fair Value (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValueDetails2</Role>
      <ShortName>Fair Value (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>40603 - Disclosure - Fair Value (Details 3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValueDetails3</Role>
      <ShortName>Fair Value (Details 3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40604 - Disclosure - Fair Value (Details 4)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureFairValueDetails4</Role>
      <ShortName>Fair Value (Details 4)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureInventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Impairment of Long-Lived Assets and Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureImpairmentOfLongLivedAssetsAndGoodwillDetails</Role>
      <ShortName>Impairment of Long-Lived Assets and Goodwill (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Long-Term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureLongTermDebtDetails</Role>
      <ShortName>Long-Term Debt (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEquityDetails</Role>
      <ShortName>Equity (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureIncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Earnings Per Common Unit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureEarningsPerCommonUnitDetails</Role>
      <ShortName>Earnings Per Common Unit (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationDetails</Role>
      <ShortName>Segment Information (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>41402 - Disclosure - Segment Information (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationDetails2</Role>
      <ShortName>Segment Information (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>41403 - Disclosure - Segment Information (Details 3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationDetails3</Role>
      <ShortName>Segment Information (Details 3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>41404 - Disclosure - Segment Information (Details 4)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationDetails4</Role>
      <ShortName>Segment Information (Details 4)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>41405 - Disclosure - Segment Information (Details 5)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSegmentInformationDetails5</Role>
      <ShortName>Segment Information (Details 5)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Supplemental Condensed Consolidating Financial Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCondensedConsolidatingFinancialInformationDetails</Role>
      <ShortName>Supplemental Condensed Consolidating Financial Information (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Supplemental Condensed Consolidating Financial Information (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCondensedConsolidatingFinancialInformationDetails2</Role>
      <ShortName>Supplemental Condensed Consolidating Financial Information (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>41503 - Disclosure - Supplemental Condensed Consolidating Financial Information (Details 3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCondensedConsolidatingFinancialInformationDetails3</Role>
      <ShortName>Supplemental Condensed Consolidating Financial Information (Details 3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Supplemental Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.markwest.com/role/DisclosureSupplementalCashFlowInformationDetails</Role>
      <ShortName>Supplemental Cash Flow Information (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Element mwe_DebtInstrumentCovenantTotalLeverageRatioPriorToCollateralReleaseDate had a mix of decimals attribute values: 1 2.</Log>
    <Log type="Info">Element mwe_LimitedPartnerMaximumValueOfferingLimitedPartnerUnits had a mix of decimals attribute values: -9 -8.</Log>
    <Log type="Info">Element us-gaap_AssetImpairmentCharges had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_PaymentOfFinancingAndStockIssuanceCosts had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_ProceedsFromIssuanceOfCommonLimitedPartnersUnits had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">'Monetary' elements on report '40301 - Disclosure - Variable Interest Entity (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40401 - Disclosure - Other Equity Interests (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40801 - Disclosure - Impairment of Long-Lived Assets and Goodwill (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40901 - Disclosure - Long-Term Debt (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41001 - Disclosure - Equity (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Shares' elements on report '41301 - Disclosure - Earnings Per Common Unit (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41301 - Disclosure - Earnings Per Common Unit (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41601 - Disclosure - Supplemental Cash Flow Information (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 00100 - Statement - Condensed Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2013'</Log>
    <Log type="Info">Process Flow-Through: 00105 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2013'</Log>
    <Log type="Info">Process Flow-Through: 00200 - Statement - Condensed Consolidated Statements of Operations</Log>
    <Log type="Info">Process Flow-Through: 00400 - Statement - Condensed Consolidated Statements of Cash Flows</Log>
  </Logs>
  <InputFiles>
    <File>mwe-20150331.xml</File>
    <File>mwe-20150331.xsd</File>
    <File>mwe-20150331_cal.xml</File>
    <File>mwe-20150331_def.xml</File>
    <File>mwe-20150331_lab.xml</File>
    <File>mwe-20150331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
