Commitments And Contingencies (Details) a in Millions, CAD in Millions	1 Months Ended			9 Months Ended
	Sep. 30, 2015 CAD plaintiff item	Jul. 31, 2013 USD ($)	Aug. 31, 2011 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) item	Dec. 31, 2010 USD ($)	Mar. 31, 2010 CAD a
Commitments And Contingencies [Line Items]
Investment in New Brunswick towards Company's commitment	CAD 45				$ 44,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services					605,000,000
Unrecorded capital investments obligation, Exploration program acres coverage (acres) | a							2.5
Unrecorded capital investments obligation | CAD							CAD 47
Unrecorded promissory note payable | CAD							CAD 45
Promissory note payable, liability recognized					0
Obligation under transportation agreements				$ 8,800,000,000
Litigation settlement, gross			$ 11,000,000
Litigation, portion of profits considered for disgorgement						$ 382,000,000
Disgorgement damages awarded in favor of the plaintiff and intervenor			24,000,000
Litigation, interest and attorney's fees claimed by plaintiffs			$ 9,000,000			$ 11,000,000
Disgorgement recoverable by plaintiff to be reversed		$ 24,000,000
Actual damages recoverable by plaintiff to be reversed		$ 11,000,000
Purchase Commitment [Member] | Access Capacity on Future Projects Concentration Risk [Member]
Commitments And Contingencies [Line Items]
Concentration percentage				36.00%
Arkansas Royalty Litigation [Member]
Commitments And Contingencies [Line Items]
Loss contingency, range of possible loss, minimum					$ 200,000,000
Number of cases | item	3				3
Arkansas Royalty Litigation [Member] | Arkansas State Court 2010 and 2013 [Member]
Commitments And Contingencies [Line Items]
Number of cases | item	2				2
Arkansas Royalty Litigation [Member] | Federal Court 2014 [Member]
Commitments And Contingencies [Line Items]
Number of cases | item	1				1
Arkansas Royalty Litigation [Member] | Arkansas State Court 2015 [Member]
Commitments And Contingencies [Line Items]
Number of plaintiffs | plaintiff	248
Number of cases | item	3				3