Severance (Details) - Employee severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Severance [Roll Forward]
Balance at the beginning of the period	$ 63	$ 33
Accrued to expense	17	66
Payments, net	(53)	(36)
Balance at the end of the period	$ 27	$ 63