Employee Separation Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Separation charges	$ 0	$ 15
Employee Separation Charges
Liability balance at beginning of year	10	0
Increase in liability (separation charges)	0	15
Reduction in liability (payments)	(10)	(5)
Liability balance at end of year	$ 0	$ 10