Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 10	$ 3
E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	10	3
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Severance (including payroll taxes)	10	2
Office consolidation	0	1
Total restructuring charges	10	3
Workforce Reduction | E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 10	$ 3