Financial Instruments and Fair Value - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis by Balance Sheet Grouping (Detail) (USD $) In Millions, unless otherwise specified	Jan. 25, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 2,012.3
Short-term investments	3,642.2
Other current assets	8.1
Other non-current assets	63.9
Total	5,726.5
Other current liabilities	5.2
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	1,819.4
Short-term investments	233.3
Other current assets	5.9
Other non-current assets	21.7
Total	2,080.3
Other current liabilities	0
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	192.9
Short-term investments	3,408.9
Other current assets	2.2
Other non-current assets	0
Total	3,604.0
Other current liabilities	5.2
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Short-term investments	0
Other current assets	0
Other non-current assets	42.2
Total	42.2
Other current liabilities	$ 0