Commitments And Contingencies (Narrative) (Details)	1 Months Ended			3 Months Ended
	Sep. 30, 2015 plaintiff item	Jul. 31, 2013 USD ($)	Aug. 31, 2011 USD ($)	Mar. 31, 2016 USD ($) item	Dec. 31, 2010 USD ($)
Commitments And Contingencies [Line Items]
Obligation under transportation agreements				$ 8,600,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services				861,000,000
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
Indemnification liability				0
Access Capacity on Future Projects Concentration Risk [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements				$ 3,300,000,000
Arkansas Royalty Litigation [Member]
Commitments And Contingencies [Line Items]
Number of cases | item				3
Arkansas Royalty Litigation [Member] | Arkansas State Court 2010 and 2013 [Member]
Commitments And Contingencies [Line Items]
Number of cases | item				2
Arkansas Royalty Litigation [Member] | Federal Court 2014 [Member]
Commitments And Contingencies [Line Items]
Number of cases | item				1
Loss contingency, range of possible loss, minimum				$ 100,000,000
Arkansas Royalty Litigation [Member] | Arkansas State Court 2015 [Member]
Commitments And Contingencies [Line Items]
Number of cases | item	3
Number of plaintiffs | plaintiff	248