Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator
Net income	$ 158.0	$ 221.1	$ 238.2	$ 331.7
Denominator
Weighted-average shares used to compute basic net income per share	389.9	470.3	398.4	478.1
Dilutive effect of employee stock awards	7.3	6.2	7.7	9.2
Weighted-average shares used to compute diluted net income per share	397.2	476.5	406.1	487.3
Net income per share:
Basic, in dollars per share	$ 0.41	$ 0.47	$ 0.60	$ 0.69
Diluted, in dollars per share	$ 0.40	$ 0.46	$ 0.59	$ 0.68
Net Income per Share Textuals
Potential anti-dilutive shares	3.7	28.0	4.8	26.8