Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1	$ 2	$ 7	$ 12
E&P
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1	2	7	12
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Severance (including payroll taxes)	1	2	7	12
Restructuring charges			7
Workforce Reduction | E&P
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1	$ 2	$ 7	$ 12