Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 0	$ 0	$ 41
Severance and other termination benefits
Restructuring Cost and Reserve [Line Items]
Total restructuring charges			22
Facilities-related
Restructuring Cost and Reserve [Line Items]
Total restructuring charges			1
Asset impairments
Restructuring Cost and Reserve [Line Items]
Total restructuring charges			8
Other
Restructuring Cost and Reserve [Line Items]
Total restructuring charges			$ 10