Restructuring - Changes in Restructuring Liability (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)
Employee Termination Costs
Restructuring Reserve [Roll Forward]
Restructuring liability, Beginning Balance	$ 18
Restructuring liability, Ending Balance	15
2020 MA Strategic Reorganization Restructuring Program
Restructuring Reserve [Roll Forward]
Restructuring liability, Ending Balance	15
2020 MA Strategic Reorganization Restructuring Program | Employee Termination Costs
Restructuring Reserve [Roll Forward]
Cost incurred and adjustments	2
Cash payments and adjustments	(5)
Cumulative expense incurred to date	$ 20