Restructuring Charges (Summary of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 0	$ 0	$ 0	$ 41
Severance
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