Earnings Per Share - Reconciliation of Weighted Average Number of Shares of Common Stock Outstanding In Calculating EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 25	$ 55	$ 65	$ 119
Denominator:
Weighted average shares used to compute Basic EPS	138,779	145,678	140,961	145,618
Weighted average effect of dilutive securities:
Stock options	193	1,135	312	1,229
RSUs	416	404	408	314
Weighted average shares used to compute Diluted EPS	139,388	147,217	141,681	147,161
Basic EPS	$ 0.18	$ 0.38	$ 0.46	$ 0.82
Diluted EPS	$ 0.18	$ 0.37	$ 0.46	$ 0.81