Summary of Short-term and Non-current Investments by Maturity Date (Detail) (USD $) In Millions, unless otherwise specified	Oct. 29, 2011	Jul. 30, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	$ 45.7	$ 54.1
Available-for-sale investments maturities 1 to 3 years	109.6	102.7
Available-for-sale investments maturities over 3 years	36.3	35.8
Available-for-sale investments, Total	191.6	192.6
Available-for-sale investments - short-term
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	43.8	54.1
Available-for-sale investments, Total	43.8	54.1
Available-for-sale investments - short-term | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	42.4	52.7
Available-for-sale investments, Total	42.4	52.7
Available-for-sale investments - short-term | Restricted cash
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	1.4	1.4
Available-for-sale investments, Total	1.4	1.4
Available-for-sale investments - non-current
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities 1 to 3 years	109.6	102.7
Available-for-sale investments maturities over 3 years	36.3	35.8
Available-for-sale investments, Total	145.9	138.5
Available-for-sale investments - non-current | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities 1 to 3 years	109.6	102.7
Available-for-sale investments maturities over 3 years	27.4	23.8
Available-for-sale investments, Total	137.0	126.5
Available-for-sale investments - non-current | Auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities over 3 years	8.9	12.0
Available-for-sale investments, Total	8.9	12.0
Other non-current investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	1.9
Available-for-sale investments, Total	1.9
Total non-current investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments maturities less than 1 year	1.9
Available-for-sale investments maturities 1 to 3 years	109.6	102.7
Available-for-sale investments maturities over 3 years	36.3	35.8
Available-for-sale investments, Total	$ 147.8	$ 138.5