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Investments - Additional Information (Detail) (USD $)
In Billions, unless otherwise specified
6 Months Ended
Jan. 26, 2013
Jan. 28, 2012
Disclosure Investments Additional Information [Abstract]    
Average Balance Of Securities Lending $ 0.8 $ 0.4
Fair Value Of Securities Received As Collateral That Can Be Resold Or RePledged Percentage 102.00%