Net Income per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Numerator
Net income	$ 91.0	$ 16.3
Denominator
Weighted-average shares used to compute basic net income per share	504.7	527.2
Effect of dilutive securities:
Dilutive effect of employee stock awards	8.0	6.5
Weighted-average shares used to compute diluted net income per share	512.7	533.7
Net income per share:
Basic	$ 0.18	$ 0.03
Diluted	$ 0.18	$ 0.03
Net Income per Share Textuals
Anti-dilutive shares excluded from computation of diluted earnings per share	24.7	30.6

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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