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Investments (Additional Information) (Details)
entity in Millions
3 Months Ended 9 Months Ended
Apr. 29, 2017
USD ($)
entity
Apr. 30, 2016
USD ($)
Apr. 29, 2017
USD ($)
entity
Apr. 30, 2016
USD ($)
Jul. 30, 2016
USD ($)
Schedule of Investments [Line Items]          
Impairment charges of available-for-sale investments $ 73,000,000 $ 0 $ 73,000,000 $ 3,000,000  
Other than temporary impairment, credit losses recognized in earnings, credit losses on debt securities held 0   0    
Average daily balance of securities lending     $ 800,000,000 $ 600,000,000  
Fair value of securities received as collateral that can be resold or repledged, percentage (at least)     102.00%    
Secured lending transactions outstanding $ 0   $ 0   $ 0
Number of variable interest entities required to be consolidated | entity 0.0   0.0    
Investments in privately held companies $ 950,000,000   $ 950,000,000   $ 1,003,000,000
Funding commitments 170,000,000   170,000,000    
Variable Interest Entity, Not Primary Beneficiary          
Schedule of Investments [Line Items]          
Investments in privately held companies $ 547,000,000   $ 547,000,000