Commitments and Contingencies (Narrative) (Details)	Jun. 30, 2018 USD ($)
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 9,328,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services	835,000,000
Indemnification liability	0
Pending Regulatory Approval and/or Construction [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 3,566,000,000