Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012 Mcfe
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage Of Proved Reserve Volumes That Are Natural Gas					70.00%
Natural Gas Percent Of Sales	75.00%				80.00%
Additional Proved Developed And Undeveloped Reserves Revisions Of Previous Estimates Increase Decrease					3,100,000,000,000
Additional Proved Developed And Undeveloped Reserve Revisions of Previous Estimates, Percentage Increase or Decrease					17.00%
Drilling Rigs Sold			8
Gain (Loss) on Sale of Property Plant Equipment	$ 109	$ 0	$ 158	$ 2
Natural Gas Processing Plant [Member] | Granite Wash Midstream Gas Services, L.L.C. [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	245		245
Gain (Loss) on Sale of Property Plant Equipment	106		106
Natural Gas Trades
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Hedged Price			3.70
Crude Oil
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Hedged Price			95.64
Year of 2013 [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of Capital Expenditures	45.00%		45.00%
Year of 2013 [Member] | Natural Gas Trades
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of Hedged Production			79.00%
Year of 2013 [Member] | Crude Oil
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of Hedged Production			94.00%
Property, Plant and Equipment, Other Types
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Proceeds from Sale of Property, Plant, and Equipment			$ 27