Commitments and Contingencies (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 8,994,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services	403,000,000
Contractual commitments assumed by buyer	188,000,000
Potential amount to be reimbursed to buyer	94,000,000
Liability for estimated future payments	78,000,000	$ 88,000,000
Indemnification liability	0
Pending regulatory approval and/or construction
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	1,411,000,000
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	357,000,000
Reimbursed by seller	$ 133,000,000