Segment Information (Details 4) (USD $)	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment information
Management fee revenues unconsolidated affiliate	$ 1,000,000	$ 1,500,000	$ 1,400,000
Southwest Segment
Segment information
Revenue deferral adjustment	800,000	800,000	7,200,000
Northeast Segment
Segment information
Revenue deferral adjustment	$ 6,400,000	$ 6,600,000	$ 8,200,000

The difference between the revenue recognized on the consolidated financial statements and the recognized for segment purposes. Certain contracts in which more consideration is received in the initial years than in later years and GAAP requires the entity to recognize the revenue evenly over the term of the contract by deferring revenue in the initial years. The chief operating decision maker evaluates segment performance and makes decisions based on the actual consideration received and therefore the segment revenues do not reflect the revenue deferral.

No definition available.

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