This element represents the actual amount of the VIE's capital that the non-controlling interest owners have funded.

No definition available.

Name:	mwe_ActualCapitalContributedByNoncontrollingOwners
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of capital contributed during the period.

+ References

No definition available.

+ Details

Name:	mwe_AggregateCapitalContribution
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents 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.

+ References

No definition available.

+ Details

Name:	mwe_AggregateContributionsToVIEThreshold
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The 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.

+ References

No definition available.

+ Details

Name:	mwe_AggregateRequiredCapitalContributedByNoncontrollingOwnersBeforeEntityOptionToContribute
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of retained VIE's capital requirements that the partnership contributed under the joint venture agreement.

+ References

No definition available.

+ Details

Name:	mwe_CapitalContributionByPartnershipRetained
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the aggregate net amount of contribution made to a joint venture during the period.

+ References

No definition available.

+ Details

Name:	mwe_ContributionsToConsolidatedJointVenture
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the distribution received as reimbursement for temporary funding under the joint venture agreement.

+ References

No definition available.

+ Details

Name:	mwe_DistributionReceivedAsReimbursementForTemporaryFunding
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This 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.

+ References

No definition available.

+ Details

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

- Definition

This 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.

+ References

No definition available.

+ Details

Name:	mwe_MinimumCapitalContributedByNoncontrollingOwners
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents the special non-cash allocation of income to non-controlling interest during the period.

+ References

No definition available.

+ Details

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

- Definition

The 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.

+ References

No definition available.

+ Details

Name:	mwe_NoncontrollingOwnersPreferenceThreshold
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the number of managers consisted in board of managers prior to the condensate equalization date.

+ References

No definition available.

+ Details

Name:	mwe_NumberOfManagersConsistedInBoardPriorToCondensateEqualizationDate
Namespace Prefix:	mwe_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the ownership percentage determined under Required True Up Transaction.

+ References

No definition available.

+ Details

Name:	mwe_OwnershipPercentageDeterminedUnderRequiredTrueUpTransaction
Namespace Prefix:	mwe_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents 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.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of capital funding required by the reporting entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of capital funding required by the reporting entity after the non-controlling interest owner has contributed $950 million.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of the VIE's capital requirements that the reporting entity temporarily funded on behalf of the non-controlling interest owners.

+ References

No definition available.

+ Details

Name:	mwe_TemporaryCapitalContributedByPartnershipActual
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum amount of capital funding obligation of the non-controlling interest temporarily funded by the Partnership, per an amendment to the original agreement.

+ References

No definition available.

+ Details

Name:	mwe_TemporaryCapitalContributionsByReportingEntityMaximum
Namespace Prefix:	mwe_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the option available to acquire voting interest as a percentage of the variable interest entity.

+ References

No definition available.

+ Details

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

- Definition

This 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.

+ References

Reference 1: 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

+ Details

Name:	us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

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 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

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=28200181&loc=SL6759159-111685

+ Details

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Variable Interest Entities (Details) (USD $)	12 Months Ended							12 Months Ended					12 Months Ended
Variable Interest Entities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 EMG item	Dec. 31, 2013 Ohio Gathering Blackhawk	Dec. 31, 2013 Maximum Ohio Gathering Blackhawk	Dec. 31, 2013 Maximum Ohio Condensate Summit	Dec. 31, 2013 MarkWest Utica EMG	Jan. 02, 2012 MarkWest Utica EMG	Dec. 31, 2013 MarkWest Utica EMG Maximum	Dec. 31, 2013 MarkWest Utica EMG Maximum Ohio Gathering Blackhawk	Dec. 31, 2013 MarkWest Utica EMG Minimum Ohio Gathering	Dec. 31, 2013 Equity Method Investment MarkWest Pioneer	Dec. 31, 2009 Equity Method Investment MarkWest Pioneer	Dec. 31, 2013 Utica Condensate item	Dec. 31, 2013 Utica Condensate Assets under construction	Dec. 31, 2013 Utica Condensate EMG
Variable Interest Entities
Noncontrolling interest owners total funding commitment								$ 950,000,000	$ 500,000,000
Noncontrolling interest owners initial funding commitment to VIE								750,000,000
Percentage of initial capital funding of VIE										60.00%
Percentage of capital required by reporting entity after non-controlling interest minimum contribution								100.00%
Aggregate contributions to VIE threshold								2,000,000,000
Percentage of ownership interest in joint venture maximum								70.00%
Minimum Percentage of ownership interest held by non-controlling interest								30.00%
Percentage of capital contribution to maintain ownership percentage										10.00%
Noncontrolling interest owners actual contribution								950,000,000
Contribution by the Partnership								566,500,000
Noncontrolling interest owners capital contribution preference threshold								500,000,000
Accrual of preference amount to EMG Utica's investment balance during the period								23,200,000
Minimum percentage of ownership interest held in joint venture								51.00%
Percentage of available cash to be received by the Partnership								60.00%
Maximum temporary funding by reporting entity								150,000,000
Temporary capital contributed by partnership								76,200,000
Distribution received as reimbursement for temporary funding								61,200,000
Capital contributed by partnership retained								15,000,000
Percentage of ownership interest held by the parent					99.00%							99.00%
Percentage of ownership interest held by non-controlling interest				45.00%	1.00%						1.00%		50.00%	50.00%	55.00%
Option available to acquire voting interest (as a percent)						40.00%	40.00%
Percentage of capital required by the reporting entity				100.00%													100.00%
Total capital contribution				125,000,000													100,000,000
Number of managers consisted in board of managers prior to the condensate equalization date				3											3
Ownership percentage determined under required true up transaction															55.00%
Proceeds from sale of assets under construction	209,303,000	596,000	3,450,000													17,400,000
Percentage of ownership interest held in joint venture													50.00%
Impairment of investment														39,200,000
Impairment of investment, net of provision for income tax														$ 35,400,000