Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2012
Pipelines and other midstream facilities | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Pipelines and other midstream facilities | Maximum
Property, Plant and Equipment [Line Items]
Useful life	30 years
Building and Building Improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Building and Building Improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life	40 years