Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator
Net income	$ 197.7	$ 103.6	$ 435.9	$ 435.3
Denominator
Weighted-average shares used to compute basic net income per share	382.8	448.4	393.2	468.1
Dilutive effect of employee stock awards	6.4	6.4	8.0	8.9
Weighted-average shares used to compute diluted net income per share	389.2	454.8	401.2	477.0
Net income per share:
Basic, in dollars per share	$ 0.52	$ 0.23	$ 1.11	$ 0.93
Diluted, in dollars per share	$ 0.51	$ 0.23	$ 1.09	$ 0.91
Net Income per Share Textuals
Potential anti-dilutive shares	3.1	10.2	3.7	10.8