Commitments and Contingencies (Narrative) (Details) $ in Millions	Jul. 31, 2019 USD ($)	Jun. 30, 2019 USD ($) lawsuit	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 8,467
Guarantee obligations relative to the firms transportation agreements and gathering project and services		362
Contractual commitments assumed by buyer		162
Potential amount to be reimbursed to buyer		82
Liability for estimated future payments		68		$ 88
Liability Associated With Indemnification Obligation		0
Operating lease commitment		115		$ 95
Pending regulatory approval and/or construction
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 966
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements			$ 357
Reimbursed by seller			$ 133
Subsequent event
Commitments And Contingencies [Line Items]
Operating lease commitment	$ 88
Term of contract	10 years
Arkansas Royalty Litigation
Commitments And Contingencies [Line Items]
Number of class action lawsuits | lawsuit		3
Arkansas Royalty Litigation | Arkansas
Commitments And Contingencies [Line Items]
Number of class action lawsuits | lawsuit		2
Arkansas Royalty Litigation | Eastern Arkansas
Commitments And Contingencies [Line Items]
Number of class action lawsuits | lawsuit		1