Supplemental Natural Gas And Oil Information (Aggregate Amounts Of Costs Capitalized For Natural Gas And Oil Producing Activities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Natural Gas and Oil Information [Abstract]
Subject to depletion	$ 3,002	$ 2,818	$ 3,194
Costs excluded from depletion	384	272	317
Gross natural gas, NGL, and oil properties	3,386	3,090	3,511
Less accumulated depletion	2,056	1,991	2,061
Net natural gas, NGL, and oil properties	$ 1,330	$ 1,099	$ 1,450