Weighted Average Assumptions Used to Estimate Fair Values (Detail)	9 Months Ended
Feb. 29, 2012 Year	Feb. 28, 2011 Year
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Dividend yield	1.40%	1.60%
Expected volatility	29.50%	31.50%
Weighted-average expected life (in years)	5	5
Risk-free interest rate	1.40%	1.70%

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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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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