Severance (Details) - Employee severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Restructuring reserve
Balance at the beginning of the period	$ 33	$ 8
Accrued to expense	66	85
Payments, net	(36)	(60)
Balance at the end of the period	$ 63	$ 33