Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Foreign cash and investments	$ 54	$ 98
Cash and cash equivalents	62	156	$ 192	$ 394
Cost method investments	25
Cost-method investments, impairment	1	7	0
Advertising expenses	$ 18	$ 18	$ 22
Unearned compensation cost, expected to be recognized over period (years)	2 years 2 months 12 days