Oil and Natural Gas Property Transactions - VPP Volume Remaining to Be Delivered Table (Details)	3 Months Ended
	Mar. 31, 2015 Mcfe	May 31, 2011 Mcfe	Sep. 30, 2010 Mcfe	Dec. 31, 2008 Mcfe	Aug. 31, 2008 Mcfe	May 31, 2008 Mcfe	Dec. 31, 2007 Mcfe
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)	1,220,000,000,000
Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)	314,200,000,000
Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	5,200,000
Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	2,100,000
Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	1,105,000,000,000
Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	264,200,000,000
Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	14,000,000
Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	6,200,000
VPP 10 Anadarko Basin Granite Wash [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	83 months
Proved Developed Reserves (Energy)	69,600,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	1,200,000
VPP 10 Anadarko Basin Granite Wash [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	35,800,000,000
VPP 10 Anadarko Basin Granite Wash [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	4,400,000
VPP 9 Mid-Continent [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)		177,000,000,000
VPP 9 Mid-Continent [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	71 months
Proved Developed Reserves (Energy)	85,300,000,000
VPP 9 Mid-Continent [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)		1,700,000
VPP 9 Mid-Continent [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	800,000
VPP 9 Mid-Continent [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)		138,000,000,000
VPP 9 Mid-Continent [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	69,500,000,000
VPP 9 Mid-Continent [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)		4,800,000
VPP 9 Mid-Continent [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	1,800,000
VPP 8 Barnett Shale [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)			390,000,000,000
VPP 8 Barnett Shale [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	5 months
Proved Developed Reserves (Energy)	22,500,000,000
VPP 8 Barnett Shale [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)			0
VPP 8 Barnett Shale [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 8 Barnett Shale [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)			390,000,000,000
VPP 8 Barnett Shale [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	22,500,000,000
VPP 8 Barnett Shale [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)			0
VPP 8 Barnett Shale [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 4 Anadarko and Arkoma Basins [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)				98,000,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	21 months
Proved Developed Reserves (Energy)	13,700,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)				500,000
VPP 4 Anadarko and Arkoma Basins [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	100,000
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)				95,000,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	13,300,000,000
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)				0
VPP 4 Anadarko and Arkoma Basins [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 3 Anadarko Basin [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)					93,000,000,000
VPP 3 Anadarko Basin [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	52 months
Proved Developed Reserves (Energy)	22,200,000,000
VPP 3 Anadarko Basin [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)					0
VPP 3 Anadarko Basin [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 3 Anadarko Basin [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)					93,000,000,000
VPP 3 Anadarko Basin [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	22,200,000,000
VPP 3 Anadarko Basin [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)					0
VPP 3 Anadarko Basin [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 2 Texas, Oklahoma and Kansas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)						94,000,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	49 months
Proved Developed Reserves (Energy)	12,800,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)						0
VPP 2 Texas, Oklahoma and Kansas [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)						94,000,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	12,800,000,000
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)						0
VPP 2 Texas, Oklahoma and Kansas [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 1 Kentucky and West Virginia [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Energy)							208,000,000,000
VPP 1 Kentucky and West Virginia [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Term remaining (in months)	93 months
Proved Developed Reserves (Energy)	88,100,000,000
VPP 1 Kentucky and West Virginia [Member] | Oil [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)							0
VPP 1 Kentucky and West Virginia [Member] | Oil [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0
VPP 1 Kentucky and West Virginia [Member] | Natural Gas [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)							208,000,000,000
VPP 1 Kentucky and West Virginia [Member] | Natural Gas [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	88,100,000,000
VPP 1 Kentucky and West Virginia [Member] | Natural Gas Liquids [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)							0
VPP 1 Kentucky and West Virginia [Member] | Natural Gas Liquids [Member] | Reserve Volume Remaining [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Proved Developed Reserves (Volume)	0