Restructuring Charges (Summary of Restructuring Plan) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 11	$ 30	$ 36	$ 30
Asset impairment charges and accelerated depreciation expense
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	2	25	10	25
Consulting services
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	6	0	15	0
Contract terminations
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	0	0	3	0
Severance and employee-related costs
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	2	3	3	3
Other
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 1	$ 2	$ 5	$ 2