Financial Instruments and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Oct. 24, 2014	Apr. 25, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 224.9
Short-term investments	2,364.2	2,712.3
Assets	2,649.2
Other current liabilities	(3.2)
Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	9.7
Other Noncurrent Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	50.4
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Short-term investments	97.3
Assets	130.3
Other current liabilities	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	5.6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Noncurrent Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	27.4
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	224.9
Short-term investments	2,266.9
Assets	2,495.9
Other current liabilities	(3.2)
Significant Other Observable Inputs (Level 2) | Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	4.1
Significant Other Observable Inputs (Level 2) | Other Noncurrent Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	0
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Short-term investments	0
Assets	23.0
Other current liabilities	0
Significant Unobservable Inputs (Level 3) | Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	0
Significant Unobservable Inputs (Level 3) | Other Noncurrent Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	$ 23.0