Supplemental Natural Gas And Oil Information (Changes Between The Total Standardized Measure Of Discounted Future Net Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Natural Gas and Oil Information [Abstract]
Standardized measure, beginning of period	$ 957	$ 1,098	$ 1,563
Sales and transfers of natural gas and oil produced during the year, less production costs	(291)	(345)	(466)
Net changes in prices and development costs	164	890	(443)
Extensions, discoveries and other additions, less production and development costs	82	67	46
Previously estimated development costs incurred during the period	25	23	41
Revisions of previous quantity estimates	(173)	(346)	19
Net changes in purchases and sales of proved reserves in place	3	(446)	(42)
Accretion of discount	107	114	182
Income taxes	20	(77)	220
Net changes in production rates and other	8	(21)	(22)
Standardized measure, end of period	$ 902	$ 957	$ 1,098