Commitments and Contingencies (Narrative) (Details) - USD ($)	1 Months Ended
	Feb. 29, 2020	Sep. 30, 2020	Dec. 31, 2019	Mar. 31, 2019
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 7,109,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services		1,000,000,000.0
Contractual commitments assumed by buyer		27,000,000
Potential amount to be reimbursed to buyer		13,000,000
Liability for estimated future payments		10,000,000	$ 46,000,000
Contractual commitments	$ 512,000,000
Commitment period	17 years
Material liabilities recognized		0
Pending regulatory approval and/or construction
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 405,000,000
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements				$ 357,000,000
Reimbursed by seller				$ 133,000,000