Acquisitions and Divestitures VPP Transactions (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended				3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended
	Jun. 30, 2013 Total [Member] Mcfe	Jun. 30, 2013 Natural Gas Total [Member] Mcf	Jun. 30, 2013 Oil Total [Member] MBbls	Jun. 30, 2013 NGL Reserves Total [Member] MBbls	Dec. 31, 2007 VPP 1 Kentucky and West Virginia [Member]	Dec. 31, 2007 VPP 1 Kentucky and West Virginia [Member] Total [Member] Mcfe	Dec. 31, 2007 VPP 1 Kentucky and West Virginia [Member] Natural Gas Mcf	Dec. 31, 2007 VPP 1 Kentucky and West Virginia [Member] Oil MBbls	Dec. 31, 2007 VPP 1 Kentucky and West Virginia [Member] NGL Reserves MBbls	Jun. 30, 2008 VPP 2 Texas, Oklahoma and Kansas [Member]	May 31, 2008 VPP 2 Texas, Oklahoma and Kansas [Member] Total [Member] Mcfe	May 31, 2008 VPP 2 Texas, Oklahoma and Kansas [Member] Natural Gas Mcf	May 31, 2008 VPP 2 Texas, Oklahoma and Kansas [Member] Oil MBbls	May 31, 2008 VPP 2 Texas, Oklahoma and Kansas [Member] NGL Reserves MBbls	Sep. 30, 2008 VPP 3 Anadarko Basin [Member]	Aug. 31, 2008 VPP 3 Anadarko Basin [Member] Total [Member] Mcfe	Aug. 31, 2008 VPP 3 Anadarko Basin [Member] Natural Gas Mcf	Aug. 31, 2008 VPP 3 Anadarko Basin [Member] Oil MBbls	Aug. 31, 2008 VPP 3 Anadarko Basin [Member] NGL Reserves MBbls	Dec. 31, 2008 VPP 4 Anadarko and Arkoma Basins [Member]	Dec. 31, 2008 VPP 4 Anadarko and Arkoma Basins [Member] Total [Member] Mcfe	Dec. 31, 2008 VPP 4 Anadarko and Arkoma Basins [Member] Natural Gas Mcf	Dec. 31, 2008 VPP 4 Anadarko and Arkoma Basins [Member] Oil MBbls	Dec. 31, 2008 VPP 4 Anadarko and Arkoma Basins [Member] NGL Reserves MBbls	Sep. 30, 2009 VPP 5 South Texas [Member]	Aug. 31, 2009 VPP 5 South Texas [Member] Total [Member] Mcfe	Aug. 31, 2009 VPP 5 South Texas [Member] Natural Gas Mcf	Aug. 31, 2009 VPP 5 South Texas [Member] Oil MBbls	Aug. 31, 2009 VPP 5 South Texas [Member] NGL Reserves MBbls	Mar. 31, 2010 VPP 6 East Texas and Texas Gulf Coast [Member]	Feb. 28, 2010 VPP 6 East Texas and Texas Gulf Coast [Member] Total [Member] Mcfe	Feb. 28, 2010 VPP 6 East Texas and Texas Gulf Coast [Member] Natural Gas Mcf	Feb. 28, 2010 VPP 6 East Texas and Texas Gulf Coast [Member] Oil MBbls	Feb. 28, 2010 VPP 6 East Texas and Texas Gulf Coast [Member] NGL Reserves MBbls	Sep. 30, 2010 VPP 8 Barnett Shale [Member]	Sep. 30, 2010 VPP 8 Barnett Shale [Member] Total [Member] Mcfe	Sep. 30, 2010 VPP 8 Barnett Shale [Member] Natural Gas Mcf	Sep. 30, 2010 VPP 8 Barnett Shale [Member] Oil MBbls	Sep. 30, 2010 VPP 8 Barnett Shale [Member] NGL Reserves MBbls	Jun. 30, 2011 VPP 9 Mid-Continent [Member]	May 31, 2011 VPP 9 Mid-Continent [Member] Total [Member] Mcfe	May 31, 2011 VPP 9 Mid-Continent [Member] Natural Gas Mcf	May 31, 2011 VPP 9 Mid-Continent [Member] Oil MBbls	May 31, 2011 VPP 9 Mid-Continent [Member] NGL Reserves MBbls	Mar. 31, 2012 VPP 10 Aradarko Basin Granite Wash [Member]	Mar. 31, 2012 VPP 10 Aradarko Basin Granite Wash [Member] Total [Member] Mcfe	Mar. 31, 2012 VPP 10 Aradarko Basin Granite Wash [Member] Natural Gas Mcf	Mar. 31, 2012 VPP 10 Aradarko Basin Granite Wash [Member] Oil MBbls	Mar. 31, 2012 VPP 10 Aradarko Basin Granite Wash [Member] NGL Reserves MBbls
Business Combination, Separately Recognized Transactions [Line Items]
Cash Proceeds from Volumetric Production Payment (VPP)	$ 6,031				$ 1,100					$ 622					$ 600					$ 412					$ 370					$ 180					$ 1,150					$ 853					$ 744
Proved Developed Reserves (Volume)		1,216,000,000,000	5,700,000	14,000,000			208,000,000,000	0	0			94,000,000,000	0	0			93,000,000,000	0	0			95,000,000,000	500,000	0			67,000,000,000	200,000	0			44,000,000,000	300,000	0			390,000,000,000	0	0			138,000,000,000	1,700,000	4,800,000			87,000,000,000	3,000,000	9,200,000
Proved Developed Reserves (Energy)	1,334,000,000,000					208,000,000,000					94,000,000,000					93,000,000,000					98,000,000,000					68,000,000,000					46,000,000,000					390,000,000,000					177,000,000,000					160,000,000,000