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Stock Compensation Plans - Valuation Assumptions of Stock Option Awards (Detail)	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Dividend yield	1.60%	1.40%	1.20%
Expected volatility	42.20%	40.00%	37.90%
Risk-free interest rate	1.00%	1.50%	2.80%
Expected term in years	6 years	6 years	7 years

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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