Derivative Instruments and Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2011 bbl	Jun. 30, 2011	Jan. 31, 2010
Derivative Instruments and Hedging Activities
Contracts no longer qualified for hedge accounting oil volume	480,000
Total volume of oil units	3,500,000	3,500,000
Total volume of natural gas units	9,400,000,000	9,400,000,000
Term loans payable	$ 200	$ 200	$ 200
Contract maturity period		January 2012