Net Income Per Share (Basic and Diluted Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income	$ 179.8	$ 140.0	$ 288.6	$ 231.4
Denominator:
Weighted-average shares used to compute basic net income per share (in shares)	380.4	382.8	380.6	383.0
Dilutive effect of employee stock awards (in shares)	5.2	3.5	7.0	5.6
Weighted-average shares used to compute diluted net income per share (in shares)	385.6	386.3	387.6	388.6
Net income per share
Basic (in dollars per share)	$ 0.47	$ 0.37	$ 0.76	$ 0.60
Diluted, (in dollars per share)	$ 0.47	$ 0.36	$ 0.74	$ 0.60
Anti-dilutive shares	1.0	8.0	1.3	2.7