Restructuring - Restructuring Expenses Included in Consolidated Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 0	$ 23	$ 2	$ 20
2018 Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring	0	0	0	(3)
2020 Real Estate Rationalization Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring	0	23	0	23
2020 MA Strategic Reorganization Restructuring Program
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 0	$ 0	$ 2	$ 0