Financial Instruments and Fair Value Measurements - Contractual Maturities of Debt Investments (Detail) (USD $) In Millions, unless otherwise specified	Jan. 24, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 1,155.4
Due in one through five years, Amortized Cost	1,750.1
Due after ten years, Amortized Cost	41.9	[1]
Total, Amortized Cost	2,947.4
Due in one year or less, Estimated Fair Value	1,157.5
Due in one through five years, Estimated Fair Value	1,759.1
Due after ten years, Estimated Fair Value	40.4	[1]
Total, Estimated Fair Value	$ 2,957.0

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