Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 2	$ 2	$ 12	$ 5
E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	2	2	12	5
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Severance (including payroll taxes)	2	1	12	3
Office consolidation	0	1	0	2
Total restructuring charges	2	2	12	5
Workforce Reduction | E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 2	$ 2	$ 12	$ 5