Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Total capitalized interest	$ 151	$ 132	$ 67
Maximum
Property, Plant and Equipment [Line Items]
Useful lives of gathering facilitates and processing plants (in years)	14 years
Useful lives of other property (in years)	10 years
Minimum
Property, Plant and Equipment [Line Items]
Useful lives of gathering facilitates and processing plants (in years)	5 years
Useful lives of other property (in years)	3 years