Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of Significant Accounting Policies [Abstract]
Useful lives of gathering facilitates and processing plants, lower range (in years)	5
Useful lives of gathering facilitates and processing plants, upper range (in years)	14
Useful lives of other property, lower range (in years)	3
Useful lives of other property, upper range (in years)	10
Total capitalized interest	$ 132	$ 67	$ 45
More-likely-than-not threshold, description	likelihood of more than 50 percent
Maturities, description	three months or less at the time of purchase