Acquisitions and Divestitures, VPP Volume Remaining to Be Delivered Table (Details)	Dec. 31, 2012 MBbls	Dec. 31, 2012 Natural Gas Mcf	Dec. 31, 2012 Natural Gas Reserve Volume Remaining Mcf	Dec. 31, 2012 Oil MBbls	Dec. 31, 2012 Oil Reserve Volume Remaining MBbls	Dec. 31, 2012 NGL Reserves MBbls	Dec. 31, 2012 NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Andarko Basin Granite Wash MBbls	Dec. 31, 2012 Andarko Basin Granite Wash Reserve Volume Remaining	Mar. 31, 2012 Andarko Basin Granite Wash Natural Gas Mcf	Dec. 31, 2012 Andarko Basin Granite Wash Natural Gas Reserve Volume Remaining Mcf	Mar. 31, 2012 Andarko Basin Granite Wash Oil MBbls	Dec. 31, 2012 Andarko Basin Granite Wash Oil Reserve Volume Remaining MBbls	Mar. 31, 2012 Andarko Basin Granite Wash NGL Reserves MBbls	Dec. 31, 2012 Andarko Basin Granite Wash NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Mid-Continent MBbls	Dec. 31, 2012 Mid-Continent Reserve Volume Remaining	May 31, 2012 Mid-Continent Natural Gas Mcf	Dec. 31, 2012 Mid-Continent Natural Gas Reserve Volume Remaining Mcf	May 31, 2012 Mid-Continent Oil MBbls	Dec. 31, 2012 Mid-Continent Oil Reserve Volume Remaining MBbls	May 31, 2012 Mid-Continent NGL Reserves MBbls	Dec. 31, 2012 Mid-Continent NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Barnett Shale MBbls	Dec. 31, 2012 Barnett Shale Reserve Volume Remaining	Sep. 30, 2010 Barnett Shale Natural Gas Mcf	Dec. 31, 2012 Barnett Shale Natural Gas Reserve Volume Remaining Mcf	Sep. 30, 2010 Barnett Shale Oil MBbls	Dec. 31, 2012 Barnett Shale Oil Reserve Volume Remaining MBbls	Sep. 30, 2010 Barnett Shale NGL Reserves MBbls	Dec. 31, 2012 Barnett Shale NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 East Texas And Texas Gulf Coast MBbls	Dec. 31, 2012 East Texas And Texas Gulf Coast Reserve Volume Remaining	Feb. 28, 2010 East Texas And Texas Gulf Coast Natural Gas Mcf	Dec. 31, 2012 East Texas And Texas Gulf Coast Natural Gas Reserve Volume Remaining Mcf	Feb. 28, 2010 East Texas And Texas Gulf Coast Oil MBbls	Dec. 31, 2012 East Texas And Texas Gulf Coast Oil Reserve Volume Remaining MBbls	Feb. 28, 2010 East Texas And Texas Gulf Coast NGL Reserves MBbls	Dec. 31, 2012 East Texas And Texas Gulf Coast NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 South Texas MBbls	Dec. 31, 2012 South Texas Reserve Volume Remaining	Aug. 31, 2009 South Texas Natural Gas Mcf	Dec. 31, 2012 South Texas Natural Gas Reserve Volume Remaining Mcf	Aug. 31, 2009 South Texas Oil MBbls	Dec. 31, 2012 South Texas Oil Reserve Volume Remaining MBbls	Aug. 31, 2009 South Texas NGL Reserves MBbls	Dec. 31, 2012 South Texas NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Anadarko And Arkoma Basins MBbls	Dec. 31, 2012 Anadarko And Arkoma Basins Reserve Volume Remaining	Dec. 31, 2008 Anadarko And Arkoma Basins Natural Gas Mcf	Dec. 31, 2012 Anadarko And Arkoma Basins Natural Gas Reserve Volume Remaining Mcf	Dec. 31, 2008 Anadarko And Arkoma Basins Oil MBbls	Dec. 31, 2012 Anadarko And Arkoma Basins Oil Reserve Volume Remaining MBbls	Dec. 31, 2008 Anadarko And Arkoma Basins NGL Reserves MBbls	Dec. 31, 2012 Anadarko And Arkoma Basins NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Anadarko Basin Woodford Shale MBbls	Dec. 31, 2012 Anadarko Basin Woodford Shale Reserve Volume Remaining	Aug. 31, 2008 Anadarko Basin Woodford Shale Natural Gas Mcf	Dec. 31, 2012 Anadarko Basin Woodford Shale Natural Gas Reserve Volume Remaining Mcf	Aug. 31, 2008 Anadarko Basin Woodford Shale Oil MBbls	Dec. 31, 2012 Anadarko Basin Woodford Shale Oil Reserve Volume Remaining MBbls	Aug. 31, 2008 Anadarko Basin Woodford Shale NGL Reserves MBbls	Dec. 31, 2012 Anadarko Basin Woodford Shale NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Texas, Oklahoma And Kansas MBbls	Dec. 31, 2012 Texas, Oklahoma And Kansas Reserve Volume Remaining	May 31, 2008 Texas, Oklahoma And Kansas Natural Gas Mcf	Dec. 31, 2012 Texas, Oklahoma And Kansas Natural Gas Reserve Volume Remaining Mcf	May 31, 2008 Texas, Oklahoma And Kansas Oil MBbls	Dec. 31, 2012 Texas, Oklahoma And Kansas Oil Reserve Volume Remaining MBbls	May 31, 2008 Texas, Oklahoma And Kansas NGL Reserves MBbls	Dec. 31, 2012 Texas, Oklahoma And Kansas NGL Reserves Reserve Volume Remaining MBbls	Dec. 31, 2012 Kentucky And West Virginia MBbls	Dec. 31, 2012 Kentucky And West Virginia Reserve Volume Remaining	Dec. 31, 2007 Kentucky And West Virginia Natural Gas Mcf	Dec. 31, 2012 Kentucky And West Virginia Natural Gas Reserve Volume Remaining Mcf	Dec. 31, 2007 Kentucky And West Virginia Oil MBbls	Dec. 31, 2012 Kentucky And West Virginia Oil Reserve Volume Remaining MBbls	Dec. 31, 2007 Kentucky And West Virginia NGL Reserves MBbls	Dec. 31, 2012 Kentucky And West Virginia NGL Reserves Reserve Volume Remaining MBbls
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Contract Term									110 months								98 months								32 months								85 months								49 months								48 months								79 months								76 months								120 months
Proved Developed Reserves (Volume)	699,000,000	1,216,000,000	609,000,000	5,700,000	4,000,000	14,000,000	11,000,000	127,000,000		87,000,000	68,000,000	3,000,000	2,300,000	9,200,000	7,500,000	130,000,000		138,000,000	102,000,000	1,700,000	1,200,000	4,800,000	3,500,000	164,000,000		390,000,000	164,000,000	0	0	0	0	27,000,000		44,000,000	26,000,000	300,000	200,000	0	0	25,000,000		67,000,000	24,000,000	200,000	100,000	0	0	36,000,000		95,000,000	35,000,000	500,000	200,000	0	0	39,000,000		93,000,000	39,000,000	0	0	0	0	31,000,000		94,000,000	31,000,000	0	0	0	0	120,000,000		208,000,000	120,000,000	0	0	0	0