Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Intangible Assets by Major Class
Estimated weighted-average life (in years)			4 years 3 months 18 days
Amortization of Intangible Assets	$ 1	$ 1	$ 2	$ 3