Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jul. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 8,194
Guarantee obligations relative to the firms transportation agreements and gathering project and services	323
Contractual commitments assumed by buyer	135
Potential amount to be reimbursed to buyer	70
Liability for estimated future payments	57			$ 88
Operating lease commitment	190			$ 95
Term of contract		10 years
Liability Associated With Indemnification Obligation	0
Pending regulatory approval and/or construction
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	752
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements			$ 357
Reimbursed by seller			$ 133
Office Building
Commitments And Contingencies [Line Items]
Operating lease commitment	$ 87
Term of contract	10 years