Shareholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 27, 2018	Jan. 28, 2017	Jan. 27, 2018	Jan. 28, 2017	Apr. 29, 2017	Mar. 15, 2017	Oct. 20, 2015
Class of Stock [Line Items]
Treasury stock repurchased, shares	0	311,020	0	2,019,798
Treasury stock repurchase plan		$ 3,493,000		$ 23,282,000
Treasury stock, shares	39,585,000	40,093,000	39,585,000	40,093,000	39,497,000
Treasury stock, at cost	$ 1,121,724,000	$ 1,135,299,000	$ 1,121,724,000	$ 1,135,299,000	$ 1,121,071,000
Maximum
Class of Stock [Line Items]
Number of shares authorized to be repurchase						$ 50,000,000	$ 50,000,000
Stock Repurchase Program
Class of Stock [Line Items]
Treasury stock, shares	39,584,907,000		39,584,907,000
Treasury stock, at cost	$ 1,087,067,000		$ 1,087,067,000
New Stock Repurchase Program
Class of Stock [Line Items]
Stock repurchase program, remaining authorized repurchase amount	$ 50,000,000		$ 50,000,000