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 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

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 distributions received from subsidiary.

+ References

No definition available.

+ Details

Name:	mwe_DistributionReceivedFromSubsidiary
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

Targeted percentage of aggregate investment balances for the partnership necessary to receive 60% of the cash generated by a joint venture.

+ References

No definition available.

+ Details

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

- 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 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 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

Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(k)(1))

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-Publisher SEC

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-Name Regulation S-X (SX)

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-Topic 210

-SubTopic 10

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-Paragraph 1

-Subparagraph (SX 210.5-02.3(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AccountsReceivableRelatedPartiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 3

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-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

+ Details

Name:	us-gaap_GainLossOnDispositionOfAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 cash inflow from the capital received in cash from a partner in a partnership during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

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-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

+ Details

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

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

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-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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-Name Accounting Standards Codification

-Glossary Related Parties

-URI http://asc.fasb.org/extlink&oid=16382449

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-07.1(c))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 07

-Paragraph b

-Subparagraph 1

-Article 6

+ Details

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 Entity (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		1 Months Ended		3 Months Ended	6 Months Ended	0 Months Ended	1 Months Ended		1 Months Ended
Variable Interest Entity (Details) (USD $)	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 MarkWest Utica EMG	Jun. 30, 2014 MarkWest Utica EMG	Jun. 30, 2014 MarkWest Utica EMG Summit	Jul. 31, 2014 MarkWest Utica EMG Summit Subsequent events	Jun. 30, 2014 MarkWest Utica EMG Maximum	Jun. 30, 2014 Ohio Gathering	Jun. 30, 2014 Ohio Gathering	May 30, 2014 Ohio Gathering Summit	Jan. 31, 2014 Ohio Gathering Summit	Jun. 30, 2014 Ohio Gathering Summit	Jul. 31, 2014 Ohio Gathering Summit Subsequent events	May 30, 2014 Ohio Gathering Maximum Summit
Variable Interest Entities
Noncontrolling interest owners total funding commitment					$ 950,000,000	$ 950,000,000
Percentage of capital required by reporting entity after non-controlling interest minimum contribution					100.00%	100.00%
Aggregate contributions to VIE threshold					2,000,000,000	2,000,000,000
Percentage of ownership interest in joint venture maximum					70.00%	70.00%
Minimum Percentage of ownership interest held by non-controlling interest					30.00%	30.00%
Percentage of capital contribution to maintain ownership percentage									10.00%
Noncontrolling interest owners actual contribution					950,000,000	950,000,000
Contribution by the Partnership						944,100,000
Noncontrolling interest owners capital contribution preference threshold					500,000,000	500,000,000
Accrual of preference amount to EMG Utica's investment balance during the period					9,100,000	17,900,000
Minimum percentage of ownership interest held in joint venture					51.00%	51.00%
Percentage of available cash to be received by the Partnership					60.00%	60.00%
Percentage of aggregate investment balances ownership target for the partnership					60.00%	60.00%
Percentage of ownership interest held by non-controlling interest														40.00%		1.00%
Cash investment received												324,700,000			16,500,000
Distributions received from Ohio Gathering						319,600,000
Percentage of ownership interest held in joint venture													1.00%
(Gain) loss on disposal of property, plant and equipment	1,450,000	(37,736,000)	1,357,000	(37,598,000)			(5,000,000)	(300,000)		(5,300,000)	(5,300,000)
Receivable balance	13,977,000		13,977,000							14,000,000	14,000,000
Management Fees revenue										$ 1,000,000	$ 1,000,000