Financial Instruments and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jul. 25, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 153.4
Short-term investments	2,532.6
Assets	2,749.1
Other current liabilities	(0.7)
Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	8.4
Other Noncurrent Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	54.7
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	161.9
Assets	195.4
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	5.2
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	28.3
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	153.4
Short-term investments	2,370.7
Assets	2,527.3
Other current liabilities	(0.7)
Significant Other Observable Inputs (Level 2) | Other Current Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	3.2
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	26.4
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	$ 26.4