Income Taxes - Schdule of Domestic and Foreign Income Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. income before tax	$ 279	$ 188	$ 379
Foreign income before tax	6	33	38
Income before income taxes	$ 285	$ 221	$ 417