Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended		3 Months Ended							12 Months Ended
	Mar. 31, 2013	Mar. 30, 2012	Dec. 31, 2012 Mcfe	Mar. 31, 2012	Mar. 31, 2013 Natural Gas Trades	Mar. 31, 2013 Crude Oil	Mar. 31, 2013 Year of 2013 [Member]	Mar. 31, 2013 Year of 2013 [Member] Natural Gas Trades	Mar. 31, 2013 Year of 2013 [Member] Crude Oil	Mar. 31, 2012 Year of 2012 [Member]	Dec. 31, 2012 Year of 2012 [Member] Natural Gas Trades	Dec. 31, 2012 Property, Plant and Equipment, Other Types
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of Capital Expenditures							50.00%
Hedged Price					3.72	95.43
Percentage of Hedged Production								78.00%	88.00%
Percentage Of Proved Reserve Volumes That Are Natural Gas											70.00%
Natural Gas Percent Of Sales							76.00%			80.00%
Additional Proved Developed and Undeveloped Resreves, Revisions of Previous Estmates			3,100,966,387,712
Additional Proved Developed And Undeveloped Reserve Revisions of Previous Estimates, Percentage Increase or Decrease			17.00%
Change in Natural Gas Price	45.00%
Natural Gas Price After Price Differentials	3.19			1.75
Drilling Rigs Sold			8
Proceeds from Sale of Property, Plant, and Equipment	$ 165	$ 59										$ 27