Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012 Mcfe	Sep. 30, 2013 Scenario, Forecast, Remaining 2013 [Member] Oil [Member]	Dec. 31, 2013 Scenario, Forecast [Member]	Sep. 30, 2013 Scenario, Forecast [Member] Natural Gas [Member] Mcf	Sep. 30, 2013 Scenario, Forecast [Member] Natural Gas [Member] Mcf	Sep. 30, 2013 Scenario, Forecast [Member] Oil [Member] Boe	Sep. 30, 2013 Corporate Revolving Bank Credit Facility
Concentration Risk [Line Items]
Spending Gap							$ 3,500,000,000
Borrowing capacity											4,000,000,000
Percentage Of Proved Reserve Volumes That Are Natural Gas					70.00%
Natural Gas Percent Of Sales	73.00%				80.00%
Percentage of Hedged Production								80.00%	80.00%	91.00%
Hedged Price						95.59		4.22	3.69	93.79
Proved Developed Reserves (Energy)										22
Proved Developed Reserves (Volume)								251	251
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%
Impairment of natural gas and oil properties	$ 0	$ 3,315,000,000	$ 0	$ 3,315,000,000