Net Income per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator
Net income	$ 99.1	$ 16.8	$ 288.0	$ 90.8
Denominator
Weighted-average shares used to compute basic net income per share	501.5	521.2	503.0	525.4
Dilutive effect of employee stock awards	7.1	3.3	7.7	4.9
Weighted-average shares used to compute diluted net income per share	508.6	524.5	510.7	530.3
Net income per share:
Basic (in dollars per share)	$ 0.20	$ 0.03	$ 0.57	$ 0.17
Diluted (in dollars per share)	$ 0.19	$ 0.03	$ 0.56	$ 0.17
Net Income per Share Textuals
Anti-dilutive shares excluded from computation of diluted earnings per share	21.8	36.8	22.3	33.0