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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income	$ 74	$ 54	$ 195	$ 190
Denominator:
Weighted average shares used to compute Basic EPS	144,133	142,842	143,662	142,648
Weighted average effect of dilutive securities:
Stock options	1,442	2,851	1,959	2,837
RSUs	253	378	265	354
Weighted average shares used to compute Diluted EPS	145,828	146,071	145,886	145,839
Basic EPS	$ 0.51	$ 0.38	$ 1.35	$ 1.33
Diluted EPS	$ 0.51	$ 0.37	$ 1.34	$ 1.30