2.4.0.84030 - Disclosure - Variable Interest Entity and Equity Method Investment (Details)truefalsefalse1false USDtruefalse$D2013Q2YTD_CoVenturerMemberhttp://www.sec.gov/CIK0001166036duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseVariable Interest Entity MarkWest Utica EMGdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CoVenturerMemberdei_LegalEntityAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDtruefalse$I2012Q1_M0102_CoVenturerMemberhttp://www.sec.gov/CIK0001166036instant2012-01-02T00:00:000001-01-01T00:00:00falsefalseVariable Interest Entity MarkWest Utica EMGdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CoVenturerMemberdei_LegalEntityAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false truefalseD2013Q2YTD_MarkWestPioneerMemberhttp://www.sec.gov/CIK0001166036duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseEquity Method Investment MarkWest Pioneerdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldimwe_MarkWestPioneerMemberdei_LegalEntityAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli04false USDtruefalse$D2009_MarkWestPioneerMemberhttp://www.sec.gov/CIK0001166036duration2009-01-01T00:00:002009-12-31T00:00:00falsefalseEquity Method Investment MarkWest Pioneerdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldimwe_MarkWestPioneerMemberdei_LegalEntityAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$1true 3us-gaap_VariableInterestEntityLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Variable Interest Entities and Equity Method Investment2false 4mwe_MinimumCapitalContributedByNoncontrollingOwnersmwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse950000000950000000USD$falsetruefalse2truefalsefalse500000000500000000USD$falsetruefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThis element represents the amount of the VIE's capital requirements that the non-controlling interest owners are obligated to fund under the joint venture agreement.No definition available.false2Noncontrolling interest owners total funding commitment3false 4mwe_AggregateRequiredCapitalContributedByNoncontrollingOwnersBeforeEntityOptionToContributemwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2truefalsefalse750000000750000000falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe amount that the non-controlling interest owners are required to contribute to the VIE before the reporting entity has the option to contribute up to 60% of the subsequent capital required by the VIE.No definition available.false2Noncontrolling interest owners initial funding commitment to VIE4false 4mwe_PercentageOfInitialRequiredCapitalContributionmwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.600.60falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the percentage of capital funding to the VIE that the reporting entity can elect to contribute after the non-controlling interest contributes $750 million but before the non-controlling interest has contributed $950 million.No definition available.false0Percentage of initial capital funding of VIE5false 4mwe_NoncontrollingOwnersAccrualOfPreferenceAmountmwe_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse64000006400000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the special non-cash allocation of income to non-controlling interest during the period.No definition available.false2Accrual of preference amount to EMG Utica's investment balance during the period6false 4mwe_PercentageOfRequiredCapitalContributionByReportingEntityAfterNCImwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse1.001.00falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the percentage of capital funding required by the reporting entity after the non-controlling interest owner has contributed $950 million.No definition available.false0Percentage of capital required by reporting entity after non-controlling interest minimum contribution7false 4mwe_AggregateContributionsToVIEThresholdmwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse20000000002000000000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the aggregate amount of capital contributed to the VIE from all members that must be achieved before the non-controlling interest owners have the option to contribute additional capital. Prior to reaching this threshold (and after the non-controlling interest owners have contributed $950 million) the reporting entity is required to contribute 100% of the capital requirements of the VIE.No definition available.false2Aggregate contributions to VIE threshold8false 4mwe_PercentageOfOwnershipInterestInJointVentureMaximummwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.700.70falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the maximum percentage to which the reporting entity can elect to increase its ownership interest in the VIE. The reporting entity's interest could increase above this percentage if the non-controlling interest owners elect not to maintain their ownership interest.No definition available.false0Percentage of ownership interest in joint venture maximum9false 4mwe_PercentageOfOwnershipInterestInJointVentureMinimummwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.300.30falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the maximum percentage of ownership interest in the VIE that will be held by non-controlling interest holders if the reporting entity elects to increase its ownership percentage by funding additional capital.No definition available.false0Minimum Percentage of ownership interest held by non-controlling interest10false 4mwe_PercentageOfAdditionalCapitalContributionRequiredToMaintainOwnershipInterestmwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.100.10falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the percentage of additional capital funding of the VIE the non-controlling interest owners have the right, but not obligation, to make in order to maintain its ownership interest at the level specified in the agreement after the aggregate contributions from all members reach $2 billion.No definition available.false0Maximum percentage of capital contribution to maintain ownership percentage11false 4mwe_NoncontrollingOwnersPreferenceThresholdmwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse500000000500000000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe minimum capital contributions (since inception) required of the non-controlling interest in order for it to receive a quarterly special allocation of income. The special allocation of income will be based only on amounts contributed in excess of this threshold. The quarterly allocation of income will cease after the quarter ended December 31, 2016.No definition available.false2Noncontrolling interest owners capital contribution preference threshold12false 4mwe_MinimumVariableInterestEntityOwnershipPercentagemwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.510.51falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the minimum percentage of the aggregate contributions to the VIE to be made by the Partnership. If the Partnership's contributions are below the minimum percentage as of December 31, 2016, the non-controlling interest may require the Partnership to purchase additional membership interests from the non-controlling interest until such point as the Partnership achieves the minimum percentage.No definition available.false0Minimum percentage of ownership interest held in joint venture13false 4mwe_PercentageOfCashGenerationReceivedmwe_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.600.60falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepureRepresents the percentage of cash available for distribution that the Partnership will receive from the VIE for all periods prior to the earlier of December 31, 2016 and the date at which the reporting entity has contributed 60% of the aggregate capital contributions made to the VIE. After such date, the cash available for distribution will be distributed in accordance with each members ownership percentage.No definition available.false0Percentage of available cash to be received by the Partnership14false 4mwe_TemporaryCapitalContributionsByReportingEntityMaximummwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse150000000150000000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryMaximum amount of capital funding obligation of the non-controlling interest temporarily funded by the Partnership, per an amendment to the original agreement.No definition available.false2Maximum temporary funding by reporting entity15false 4mwe_TemporaryCapitalContributedByPartnershipActualmwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse7620000076200000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the amount of the VIE's capital requirements that the reporting entity temporarily funded on behalf of the non-controlling interest owners.No definition available.false2Temporary capital contributed by partnership16false 4mwe_DistributionReceivedAsReimbursementForTemporaryFundingmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse6120000061200000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the distribution received as reimbursement for temporary funding under the joint venture agreement.No definition available.false2Distribution received as reimbursement for temporary funding17false 4mwe_CapitalContributionByPartnershipRetainedmwe_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1500000015000000falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the amount of retained VIE's capital requirements that the partnership contributed under the joint venture agreement.No definition available.false2Capital contributed by partnership retained18false 4us-gaap_VariableInterestEntityOwnershipPercentageus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.600.60falsefalsefalse2falsetruefalse00falsefalsefalse3truetruefalse0.500.50falsefalsefalse4falsetruefalse00falsefalsefalsenum:percentItemTypepurePercentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685 false0Percentage of ownership interest held in joint venture19false 4us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwnersus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsetruefalse00falsefalsefalse2falsetruefalse00falsefalsefalse3truetruefalse0.500.50falsefalsefalse4truetruefalse0.500.50falsefalsefalsenum:percentItemTypepureThe equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.No definition available.false0Percentage of ownership interest held by non-controlling interest20false 4us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairmentus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4truefalsefalse3920000039200000falsefalsefalsexbrli:monetaryItemTypemonetaryThis item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 18 -Paragraph 19 -Subparagraph h -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 35 -Paragraph 32 -URI http://asc.fasb.org/extlink&oid=7658923&loc=d3e32787-111569 false2Impairment of investment21false 4mwe_EquityMethodInvestmentOtherThanTemporaryImpairmentNetOfTaxmwe_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4truefalsefalse3540000035400000USD$falsetruefalsexbrli:monetaryItemTypemonetaryThis item represents an other than temporary decline in value, net of tax, that has been recognized against an investment accounted for under the equity method of accounting.No definition available.false2Impairment of investment, net of provision for income taxfalseVariable Interest Entity and Equity Method Investment (Details) (USD $)NoRoundingUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.markwest.com/role/DisclosureVariableInterestEntityAndEquityMethodInvestmentDetails421