Commitments and Contingencies (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) plaintiff item
Commitments And Contingencies [Line Items]
Obligation under transportation agreements | $	$ 9,125,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services | $	832,000,000
Indemnification liability | $	$ 0
Arkansas Royalty Litigation [Member] | Arkansas State Court [Member]
Commitments And Contingencies [Line Items]
Number of actions | item	2
Number of state cases set for trial | item	1
Number of cases | item	3
Number of plaintiffs | plaintiff	248
Number of cases removed to federal court | item	2
Pending Regulatory Approval and/or Construction [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements | $	$ 3,139,000,000