Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator
Net income	$ 140.0	$ 158.0	$ 231.4	$ 238.2
Denominator
Weighted-average shares used to compute basic net income per share	382.8	389.9	383.0	398.4
Dilutive effect of employee stock awards	3.5	7.3	5.6	7.7
Weighted-average shares used to compute diluted net income per share	386.3	397.2	388.6	406.1
Net income per share:
Basic, in dollars per share	$ 0.37	$ 0.41	$ 0.60	$ 0.60
Diluted, in dollars per share	$ 0.36	$ 0.40	$ 0.60	$ 0.59
Net Income per Share Textuals
Potential anti-dilutive shares	8.0	3.7	2.7	4.8