Stock-Based Compensation Plans (Schedule Of Weighted-Average Grant Date Fair Value Of Options Granted) (Details) (USD $)	6 Months Ended
Nov. 30, 2011 years	Nov. 30, 2010 years
Stock-Based Compensation Plans [Abstract]
Weighted-average grant date fair value	$ 19.72	$ 17.61
Expected volatility	0.411%	0.42%
Expected term of the option in years	10	10
Risk-free interest rate	2.97%	3.33%
Expected dividend yield	0.56%	0.86%

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.

+ References+ Details

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.

+ References+ Details