Acquisitions And Divestitures (Schedule Of Production Payments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012 MMcf	Mar. 31, 2012 Andarko Basin Granite Wash [Member] Y MMcf	May 31, 2011 Mid-Continent [Member] Y MMcf	Sep. 30, 2010 Barnett Shale [Member] MMcf Y	Jun. 30, 2010 Permian Basin [Member] MMcf Y	Feb. 28, 2010 East Texas And The Texas Gulf Coast [Member] MMcf Y	Aug. 31, 2009 South Texas [Member] Y MMcf	Dec. 31, 2008 Anadarko And Arkoma Basins [Member] MMcf Y	Aug. 31, 2008 Anadarko Basin [Member] Y MMcf	May 31, 2008 Texas, Oklahoma And Kansas [Member] MMcf Y	Dec. 31, 2007 Kentucky And West Virginia [Member] MMcf Y
Business Acquisition [Line Items]
Proceeds	$ 6,366	$ 744	$ 853	$ 1,150	$ 335	$ 180	$ 370	$ 412	$ 600	$ 622	$ 1,100
Proved Reserves (at the time of sale) ( bcfe)	1,372,000	160,000	177,000	390,000	38,000	46,000	68,000	98,000	93,000	94,000	208,000
Proceeds ($ / mcfe)	4.64	4.68	4.82	2.93	8.73	3.95	5.46	4.19	6.38	6.53	5.29
Original Term (years)		10	10	5	10	10	7.5	8	11	11	15