Severance (Details) - Employee severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Restructuring reserve
Balance at the beginning of the period	$ 6	$ 10
Accrued to expense	89	51
Payments, net	(43)	(55)
Balance at the end of the period	$ 52	$ 6