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Acquisitions - Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Issued (Details)	12 Months Ended
	Dec. 31, 2012 2012 Acquisitions, excluding Nicira	Dec. 31, 2010 All 2010 Acquisitions
Business Acquisition [Line Items]
Expected term (in years)	1 year 10 months 24 days	2 years
Expected volatility	31.60%	29.00%
Risk-free interest rate	0.30%	0.70%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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