Commitments and Contingencies (Schedule of Changes in Contract Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Loss Contingency Accrual [Roll Forward]
Beginning contract obligations	$ 468
Liabilities settled	(182)
Accretion of discount	10
Changes in estimate	64
Ending contract obligations	360
South Texas Divestiture
Loss Contingency Accrual [Roll Forward]
Deficiency fee liability	$ (321)