Goodwill and Purchased Intangible Assets, Net - Purchased Intangible Assets, Net (Detail) (USD $) In Millions, unless otherwise specified	Jan. 23, 2015	Apr. 25, 2014
Acquired Finite Lived Intangible Assets [Line Items]
Gross Assets	$ 320.3	$ 297.1
Accumulated Amortization	(215.3)	(175.6)
Net Assets	105.0us-gaap_FiniteLivedIntangibleAssetsNet	121.5us-gaap_FiniteLivedIntangibleAssetsNet
Developed Technology
Acquired Finite Lived Intangible Assets [Line Items]
Gross Assets	312.4	283.0
Accumulated Amortization	(210.0)	(162.6)
Net Assets	102.4	120.4
Customer Contracts/Relationships
Acquired Finite Lived Intangible Assets [Line Items]
Gross Assets	5.0	9.6
Accumulated Amortization	(2.5)	(9.0)
Net Assets	2.5	0.6
Trademarks and Trade Names
Acquired Finite Lived Intangible Assets [Line Items]
Gross Assets	2.9	2.9
Accumulated Amortization	(2.8)	(2.4)
Net Assets	0.1	0.5
Covenants not to Compete
Acquired Finite Lived Intangible Assets [Line Items]
Gross Assets	0	1.6
Accumulated Amortization	0	(1.6)
Net Assets	$ 0	$ 0

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_DevelopedTechnologyRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_NoncompeteAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksAndTradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: