Severance (Details) - Employee Severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 9	$ 19
Accrued to expense	37	6
Payments, net	(23)	(16)
Restructuring reserve, ending balance	$ 23	$ 9