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Summary of Changes in Equity (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jan. 28, 2012
Jan. 29, 2011
Jan. 28, 2012
Jan. 29, 2011
Stockholders Equity Note [Line Items]        
Balance at beginning of period     $ 1,158.0 $ 1,014.7 [1]
Comprehensive income:        
Net income 63.7 42.5 111.2 90.5 [1]
Foreign currency translation adjustment     (0.2)  
Net unrealized loss on available-for-sale investments     0.4 0.6 [1]
Total comprehensive income     111.4 91.1 [1]
Change in non-controlling interest       (0.1) [1]
Purchases of common stock     (37.2) (26.1) [1]
Shares issued and equity grants made pursuant to stock-based compensation plans     25.3 14.9 [1]
Balance at end of period $ 1,257.5 $ 1,094.5 [1] $ 1,257.5 $ 1,094.5 [1]
[1] Includes amounts attributable to a non-controlling interest of $1.4 million as of July 31, 2010 and $1.5 million as of January 29, 2011. The Company sold its interest in its majority-owned investment during the fourth quarter of Fiscal 2011, thereby eliminating the non-controlling interest.