Financial Instruments and Fair Value - Contractual Maturities of Debt Investments (Detail) (USD $) In Millions, unless otherwise specified	Jan. 25, 2013
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 1,456.7
Due in one through five years, Amortized Cost	2,172.4
Due after ten years, Amortized Cost	44.8	[1]
Total, Amortized Cost	3,673.9
Due in one year or less, Fair Value	1,458.7
Due in one through five years, Fair Value	2,183.5
Due after ten years, Fair Value	42.2	[1]
Total, Fair Value	$ 3,684.4

[1] Consists of auction rate securities which have contractual maturities of greater than 10 years.