Severance (Details) - Employee severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restructuring reserve
Balance at the beginning of the period	$ 8	$ 52
Accrued to expense	85	14
Payments, net	(60)	(58)
Balance at the end of the period	$ 33	$ 8