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.

No definition available.

Variable Interest Entity (Details) (USD $)	3 Months Ended	9 Months Ended			9 Months Ended	12 Months Ended
Variable Interest Entity (Details) (USD $)	Sep. 30, 2013 Variable Interest Entity MarkWest Utica EMG	Sep. 30, 2013 Variable Interest Entity MarkWest Utica EMG	Jan. 02, 2012 Variable Interest Entity MarkWest Utica EMG	Sep. 30, 2013 Variable Interest Entity MarkWest Utica EMG Maximum	Sep. 30, 2013 Equity Method Investment MarkWest Pioneer	Dec. 31, 2009 Equity Method Investment MarkWest Pioneer
Variable Interest Entities and Equity Method Investment
Noncontrolling interest owners total funding commitment	$ 950,000,000	$ 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%	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%
Maximum percentage of capital contribution to maintain ownership percentage	10.00%	10.00%
Contribution, net of distributions, related to temporary contributions		279,900,000
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	8,300,000	14,700,000
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%
Maximum temporary funding by reporting entity	150,000,000	150,000,000
Temporary capital contributed by partnership	76,200,000	76,200,000
Distribution received as reimbursement for temporary funding		61,200,000
Capital contributed by partnership retained	15,000,000	15,000,000
Percentage of ownership interest held in joint venture		60.00%			50.00%
Percentage of ownership interest held by non-controlling interest					50.00%	50.00%
Impairment of investment						39,200,000
Impairment of investment, net of provision for income tax						$ 35,400,000