Severance (Details) - Employee severance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Restructuring reserve
Balance at the beginning of the period	$ 10	$ 5
Accrued to expense	51	44
Payments, net	(55)	(39)
Balance at the end of the period	$ 6	$ 10