Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Oct. 29, 2011		Jul. 30, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value	$ 188.3		$ 191.2
Municipal bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value	179.4	[1]	179.2	[1]
Auction rate securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value	$ 8.9	[2]	$ 12.0	[2]

[1] Based on Level 1 measurements.

[2] Based on Level 3 measurements.