Commitments and Contingencies (Narrative) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2018	Sep. 30, 2018
Commitments And Contingencies [Line Items]
Obligation under transportation agreements			$ 9,198,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services			559,000,000
Contractual commitments assumed by buyer		$ 564,000,000	564,000,000
Indemnification liability			0
Pending Regulatory Approval and/or Construction [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements			$ 3,455,000,000
Scenario, Forecast [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 126,000,000