Summary of Weighted-Average Assumptions (Director and Employee Stock Option Plans) (Detail)	12 Months Ended
Apr. 28, 2012 Year	Apr. 30, 2011 Year	Apr. 24, 2010 Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%
Director And Employee Stock Option Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	1.50%	1.20%
Expected stock price volatility	33.00%	38.00%	32.70%
Risk-free interest rate	2.50%	3.60%	2.70%
Expected life of options (years)	7.4	8.8	8.3

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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