Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 3	$ 0
E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	3
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring liability	2		$ 5
Severance (including payroll taxes)	2
Office consolidation	1
Total restructuring charges	3
Workforce Reduction | E&P
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 3