Stockholders Equity - Number and Value of Shares Netted for Employee Taxes (Detail) (Restricted Stock Units, USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Oct. 26, 2012	Oct. 28, 2011	Oct. 26, 2012	Oct. 28, 2011
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for taxes	0.1	0.1	0.7	0.6
Fair value of shares withheld and retired	$ 2.8	$ 2.5	$ 22.6	$ 27.8

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

No definition available.

Name:	us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration