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Stock Purchase and Award Plans , Valuation Assumptions (Details) - $ / shares
12 Months Ended
Apr. 28, 2017
Apr. 29, 2016
Apr. 24, 2015
Fair Value Assumptions Used in Black-Scholes Model      
Weighted average fair value of options granted (per share) $ 14.70 $ 13.72 $ 25.39
Expected life (years) 6 years 2 months 4 days 5 years 11 months 10 days 4 years 2 months 27 days
Risk-free interest rate 1.26% 1.79% 0.99%
Volatility 21.07% 21.00% 21.29%
Dividend yield 1.97% 1.96% 1.66%