Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net income
Net income	$ 108.8	$ 91.4
Denominator:
Weighted-average shares used to compute basic net income per share (in shares)	380.9	383.2
Dilutive effect of employee stock awards (in shares)	7.1	6.1
Weighted-average shares used to compute diluted net income per share (in shares)	388.0	389.3
Net income per share
Basic, in dollars per share	$ 0.29	$ 0.24
Diluted, in dollars per share	$ 0.28	$ 0.23
Anti-dilutive shares	1.6	4.0