Commitments and Contingencies (Narrative) (Details)	12 Months Ended	24 Months Ended
	Dec. 31, 2018 USD ($) lawsuit item	Dec. 31, 2020 USD ($)	Jan. 31, 2019 USD ($)
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 8,794,000,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services	463,000,000
Operating leases, future minimum payments, 2019	38,000,000
Operating leases, future minimum payments, 2020	28,000,000
Operating leases, future minimum payments, 2021	14,000,000
Operating leases, future minimum payments, 2022	6,000,000
Operating leases, future minimum payments, 2023	5,000,000
Operating leases, future minimum payments, thereafter	4,000,000
Indemnification liability	0
Access Capacity on Future Projects Concentration Risk [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 3,100,000,000
Appalachian Basin [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements			$ 357,000,000
Obligation under transportation agreements, reimbursed by seller			$ 133,000,000
Arkansas Royalty Litigation [Member]
Commitments And Contingencies [Line Items]
Number of cases | lawsuit	3
Arkansas Royalty Litigation [Member] | Arkansas State Court [Member]
Commitments And Contingencies [Line Items]
Number of cases | lawsuit	2
Pending Regulatory Approval and/or Construction [Member]
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 3,079,000,000
Exploration and Production [Member]
Commitments And Contingencies [Line Items]
Operating leases, future minimum payments, 2019	3,000,000
Operating leases, future minimum payments, 2020	1,000,000
Operating leases, future minimum payments, 2021	$ 1,000,000
Exploration and Production [Member] | Pressure Pumping Equipment [Member]
Commitments And Contingencies [Line Items]
Number of leases | item	1
Lease expiration date	Dec. 31, 2021
Aggregate annual lease payment	$ 7,000,000
Exploration and Production [Member] | Drilling Rigs [Member]
Commitments And Contingencies [Line Items]
Number of leases | item	7
Lease expiration date	Dec. 31, 2024
Aggregate annual lease payment	$ 13,000,000
Fayetteville Shale [Member]
Commitments And Contingencies [Line Items]
Contractual commitments assumed by buyer	221,000,000
Liability for estimated future payments	$ 88,000,000
Fayetteville Shale [Member] | Scenario, Forecast [Member]
Commitments And Contingencies [Line Items]
Potential amount to be reimbursed to buyer		$ 102,000,000
Fayetteville Shale [Member] | Scenario, Forecast [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Potential amount to be reimbursed to buyer		$ 102,000,000