Oil and Natural Gas Property Transactions - VPP Volumes Produced During Period Table (Details)	3 Months Ended
	Mar. 31, 2015 Mcfe	Mar. 31, 2014 Mcfe
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	31,300,000,000	39,400,000,000
Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	137,600	182,700
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	28,300,000,000	35,500,000,000
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	373,300	451,700
VPP 10 Anadarko Basin Granite Wash [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	4,400,000,000	5,500,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	83,000	109,000
VPP 10 Anadarko Basin Granite Wash [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	2,200,000,000	2,800,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	276,300	345,200
VPP 9 Mid-Continent [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	4,500,000,000	4,900,000,000
VPP 9 Mid-Continent [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	43,600	49,000
VPP 9 Mid-Continent [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	3,700,000,000	4,000,000,000
VPP 9 Mid-Continent [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	97,000	106,500
VPP 8 Barnett Shale [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	14,000,000,000	15,700,000,000
VPP 8 Barnett Shale [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 8 Barnett Shale [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	14,000,000,000	15,700,000,000
VPP 8 Barnett Shale [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 6 East Texas and Texas Gulf Coast [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)		1,200,000,000
VPP 6 East Texas and Texas Gulf Coast [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		6,000
VPP 6 East Texas and Texas Gulf Coast [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		1,100,000,000
VPP 6 East Texas and Texas Gulf Coast [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		0
VPP 5 South Texas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)		1,800,000,000
VPP 5 South Texas [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		6,300
VPP 5 South Texas [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		1,700,000,000
VPP 5 South Texas [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production		0
VPP 4 Anadarko and Arkoma Basins [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	2,100,000,000	2,400,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	11,000	12,400
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	2,100,000,000	2,300,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 3 Anadarko Basin [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	1,700,000,000	1,900,000,000
VPP 3 Anadarko Basin [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 3 Anadarko Basin [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	1,700,000,000	1,900,000,000
VPP 3 Anadarko Basin [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 2 Texas, Oklahoma and Kansas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	1,100,000,000	2,400,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	1,100,000,000	2,400,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 1 Kentucky and West Virginia [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserve, Production (Energy)	3,500,000,000	3,600,000,000
VPP 1 Kentucky and West Virginia [Member] | Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0
VPP 1 Kentucky and West Virginia [Member] | Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	3,500,000,000	3,600,000,000
VPP 1 Kentucky and West Virginia [Member] | Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Production	0	0