Name:	mwe_CashTerminationFeeUnderMergerAgreement
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Cash contribution from the parent of the acquiring entity's general partner for use as consideration in the acquisition under a merger agreement.

No definition available.

Name:	mwe_MergerAgreementContributionFromParentOfGeneralPartner
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The number of directors by which the acquiring entity's general partner's board of directors is to be increased under the terms of the merger agreement.

No definition available.

Name:	mwe_MergerAgreementIncreaseInNumberOfDirectorsOfGeneralPartner
Namespace Prefix:	mwe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of directors identified by the acquiree for appointment to the board of directors of the parent of the acquiring entity's general partner under the terms of the merger agreement.

No definition available.

Name:	mwe_MergerAgreementNumberOfDirectorsForParentOfGeneralPartnerToBeIdentifiedByAcquiree
Namespace Prefix:	mwe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of directors identified by the acquiree for appointment to the acquiring entity's general partner's board of directors under the terms of the merger agreement.

No definition available.

Name:	mwe_MergerAgreementNumberOfDirectorsOfGeneralPartnerToBeIdentifiedByAcquiree
Namespace Prefix:	mwe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Of the directors to be identified by the acquiree for appointment to the acquiring entity's general partner's board of directors under the terms of the merger agreement, the number that are to be independent under the NYSE rules.

No definition available.

Name:	mwe_MergerAgreementNumberOfIndependentDirectorsOfGeneralPartnerToBeIdentifiedByAcquiree
Namespace Prefix:	mwe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Period of the lock-up agreement under the merger agreement, during which certain conversion and transfer restriction are applied to the related partnership units.

No definition available.

Name:	mwe_MergerAgreementPeriodOfLockUpAgreement
Namespace Prefix:	mwe_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The percentage of ownership interest in the acquiree's partnership units held by the counterparty and agreed to vote in favor of the merger agreement.

No definition available.

Name:	mwe_PartnersCapitalAccountMergerAgreementPercentageInterestHeldByCounterparty
Namespace Prefix:	mwe_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Ratio applied to the conversion of the acquiree's existing partnership units into units of partnership interest in the acquiring entity under the terms of a merger agreement.

No definition available.

Name:	mwe_PartnersCapitalAccountMergerAgreementUnitConversionRatio
Namespace Prefix:	mwe_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

The number of the acquiree's partnership units held by the counterparty and agreed to vote in favor of the merger agreement.

No definition available.

Name:	mwe_PartnersCapitalAccountMergerAgreementUnitsHeldByCounterparty
Namespace Prefix:	mwe_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of voting equity interests acquired at the acquisition date in the business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

Name:	us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mwe_MarkWestUticaEMGCondensateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mwe_OhioCondensateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementScenarioAxis=mwe_PendingTransactionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=mwe_MplxLpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_BusinessAcquisitionAxis=mwe_MarkwestEnergyPartnersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LimitedPartnersCapitalAccountByClassAxis=mwe_PartnerCapitalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CounterpartyNameAxis=mwe_MAndRMWELibertyLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LimitedPartnersCapitalAccountByClassAxis=mwe_ClassBPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: