Subsequent Events (Details) (USD $)	12 Months Ended						1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 MarkWest Utica EMG	Dec. 31, 2012 8.75% senior notes due in April 2018	Dec. 31, 2012 6.5% senior notes due August 2021	Dec. 31, 2012 6.25% senior notes due June 2022	Jan. 31, 2013 Issuance of debt 4.50% senior unsecured notes due in July 2023	Jan. 31, 2013 Repurchase of debt	Jan. 31, 2013 Repurchase of debt 8.75% senior notes due in April 2018	Jan. 31, 2013 Repurchase of debt 6.5% senior notes due August 2021	Jan. 31, 2013 Repurchase of debt 6.25% senior notes due June 2022	Feb. 28, 2013 Amended Joint Venture Agreements MarkWest Utica EMG
Subsequent events
Aggregate principal amount of public offering							$ 1,000,000,000
Debt instrument, stated interest rate percentage				8.75%	6.50%	6.25%	4.50%		8.75%	6.50%	6.25%
Amount of debt repurchased									81,100,000	175,000,000	245,000,000
Net proceeds from public offering							986,900,000
Pre-tax loss on repurchase of debt								38,000,000
Non-cash write-off of the unamortized discount and deferred finance costs								7,000,000
Payments of premiums on redemption of long-term debt	71,377,000	9,732,000						31,000,000
Noncontrolling interest owners' total minimum funding commitment before amendment												500,000,000
Noncontrolling interest owners total contribution			500,000,000									950,000,000
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												60.00%
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%									30.00%
Percentage of capital contribution to maintain ownership percentage			30.00%									10.00%
Noncontrolling interest owners capital contribution preference threshold												500,000,000
Minimum percentage of ownership interest held in joint venture												51.00%
Percentage of available cash to be received by the Partnership												60.00%
Percentage of ownership interest held in joint venture			60.00%									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