Intangible Assets (Intangible Assets - Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Intangible Assets by Major Class
Estimated weighted-average life (in years)		4 years 2 months 12 days
Amortization of Intangible Assets	$ 1	$ 1	$ 2