Reconciliation of Numerators and Denominators Used to Calculate Basic EPS and Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Computation of Earnings Per Share [Line Items]
Net income	$ 111	$ 45	$ 289	$ 154
Weighted average shares of common stock outstanding	146	167	152	169
Dilutive effect stock-based awards	1	1	1	1
Diluted weighted average shares of common stock outstanding	147	168	153	170
Basic earnings per share attributable to common stockholders	$ 0.75	$ 0.27	$ 1.91	$ 0.91
Diluted earnings per share attributable to common stockholders	$ 0.75	$ 0.27	$ 1.90	$ 0.91