Acquisitions and Divestitures, VPP Volumes Produced During Period (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Mcfe	Jun. 30, 2012 Mcfe	Jun. 30, 2013 Mcfe	Jun. 30, 2012 Mcfe
Corporate VPP [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	43,400,000,000	54,000,000,000	88,800,000,000	103,200,000,000
Corporate VPP [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	39,000,000,000	47,000,000,000	80,000,000,000	92,000,000,000
Corporate VPP [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	221,600	504,900	458,400	873,700
Corporate VPP [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	523,200	728,300	1,079,400	1,115,600
VPP 10 Anadarko Basin Granite Wash [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	6,800,000,000	10,800,000,000	14,200,000,000	14,900,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	4,000,000,000	6,000,000,000	8,000,000,000	8,000,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	141,000	244,000	295,000	341,000
VPP 10 Anadarko Basin Granite Wash [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	379,000	565,000	786,700	782,900
VPP 9 Mid-Continent [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	5,300,000,000	6,000,000,000	10,800,000,000	12,300,000,000
VPP 9 Mid-Continent [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	4,000,000,000	5,000,000,000	9,000,000,000	9,000,000,000
VPP 9 Mid-Continent [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	54,200	63,600	110,400	130,100
VPP 9 Mid-Continent [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	144,200	163,300	292,700	332,700
VPP 8 Barnett Shale [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	17,200,000,000	20,300,000,000	35,000,000,000	41,700,000,000
VPP 8 Barnett Shale [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	17,000,000,000	20,000,000,000	35,000,000,000	42,000,000,000
VPP 8 Barnett Shale [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 8 Barnett Shale [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 7 Permian Basin [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)		1,200,000,000	0	2,000,000,000
VPP 7 Permian Basin [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)		0	0	0
VPP 7 Permian Basin [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)		168,000	0	343,000
VPP 7 Permian Basin [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)		0	0	0
VPP 6 East Texas and Texas Gulf Coast [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	1,200,000,000	1,400,000,000	2,500,000,000	2,800,000,000
VPP 6 East Texas and Texas Gulf Coast [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	1,000,000,000	2,000,000,000	3,000,000,000	3,000,000,000
VPP 6 East Texas and Texas Gulf Coast [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	6,000	6,000	12,000	12,000
VPP 6 East Texas and Texas Gulf Coast [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 5 South Texas [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	1,900,000,000	2,300,000,000	4,000,000,000	4,800,000,000
VPP 5 South Texas [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	2,000,000,000	2,000,000,000	4,000,000,000	5,000,000,000
VPP 5 South Texas [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	6,200	7,100	12,200	14,700
VPP 5 South Texas [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 4 Anadarko and Arkoma Basins [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	2,700,000,000	3,100,000,000	5,500,000,000	6,300,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	3,000,000,000	3,000,000,000	5,000,000,000	6,000,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	14,200	16,200	28,800	32,900
VPP 4 Anadarko and Arkoma Basins [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 3 Anadarko Basin [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	2,100,000,000	2,300,000,000	4,100,000,000	4,800,000,000
VPP 3 Anadarko Basin [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	2,000,000,000	2,000,000,000	4,000,000,000	5,000,000,000
VPP 3 Anadarko Basin [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 3 Anadarko Basin [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 2 Texas, Oklahoma and Kansas [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	2,600,000,000	2,900,000,000	5,300,000,000	5,800,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	3,000,000,000	3,000,000,000	5,000,000,000	6,000,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 2 Texas, Oklahoma and Kansas [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 1 Kentucky and West Virginia [Member]
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Reserves (Energy) (Duration)	3,600,000,000	3,700,000,000	7,400,000,000	7,800,000,000
VPP 1 Kentucky and West Virginia [Member] | Natural Gas
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	3,000,000,000	4,000,000,000	7,000,000,000	8,000,000,000
VPP 1 Kentucky and West Virginia [Member] | Oil
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0
VPP 1 Kentucky and West Virginia [Member] | NGL Reserves
Acquisitions, Divestitures, Joint Ventures, VPP's [Line Items]
Proved Developed and Undeveloped Reserves (Volume)	0	0	0	0