Acquisitions and Divestitures - Additional Information Narrative (Details) (USD $)	6 Months Ended							1 Months Ended		6 Months Ended				1 Months Ended	6 Months Ended	3 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2012 XTO Energy Inc. [Member] Mcfe acre	Jun. 30, 2013 Excluding Joint Ventures [Member]	Jun. 30, 2012 Excluding Joint Ventures [Member]	Jun. 30, 2013 JV Marcellus, Barnett and Utica	Jun. 30, 2012 JV Marcellus, Barnett and Utica	Jun. 30, 2010 VPP 7 Permian Basin [Member]	Jun. 30, 2012 VPP 7 Permian Basin [Member] Mcfe	Jun. 30, 2013 Corporate Joint Venture [Member] acre	Jun. 30, 2012 Corporate Joint Venture [Member]	Jun. 30, 2013 JV Utica	Jun. 30, 2012 JV Utica	Feb. 28, 2011 JV Niobrara	Jun. 30, 2013 JV Niobrara	Jun. 30, 2013 JV Mississippi Lime acre	Jun. 30, 2013 JV Mississippi Lime Oil bbl	Jun. 30, 2013 JV Mississippi Lime Natural Gas MMcf	Jun. 30, 2013 JV Mississippi Lime Payment at Closing [Member]	Jun. 30, 2013 JV Mississippi Lime Payment Remaining [Member]	Jun. 30, 2013 Corporate VPP [Member]
Business Acquisition [Line Items]
Gas and Oil Area, Developed, Net			60,000							850,000						425,000
Proceeds from divestitures of proved and unproved properties	$ 1,895,000,000	$ 1,555,000,000	$ 572,000,000	$ 815,000,000	$ 100,000,000
Current Net Production Units			25
Maximum working interest percentage allowed	2.50%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners																50.00%
Proceeds from Divestiture of Interest in Joint Venture						39,000,000	137,000,000	313,000,000		8,140,000,000			610,000,000	570,000,000		1,110,000,000			1,040,000,000	70,000,000
Percentage of Total Payment by Joint Venture Partner																			94.00%	6.00%
Transaction Costs																17,000,000
Proved Developed Reserves (Volume)																	9,600	54
Number of Joint Ventures										8
Total Drilling Carries										9,035,000,000			1,422,000,000		697,000,000	0
Oil And Gas Benefit From Drilling Carries										436,000,000	518,000,000
Percentage Reimbursed												60.00%			67.00%
Gain (Loss) on Sale of Other Assets																					$ 0
Proved Developed Reserves (Energy)									28,000,000