Stockholders Equity - Number and Value of Shares Netted for Employee Taxes (Detail) (Restricted Stock Units, USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for taxes	0.4	0.4	1.1	1.0
Fair value of shares withheld	$ 12.2	$ 16.4	$ 34.8	$ 44.2

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