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Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Apr. 30, 2016
Jan. 31, 2016
Apr. 30, 2015
Apr. 30, 2016
Apr. 30, 2015
Jul. 31, 2015
Income Tax Disclosure [Abstract]            
Tax benefit for research credits   $ 12        
Effective tax rate 34.00%   38.00% 33.00% 39.00%  
Effective income tax rate reconciliation, excluding discrete tax benefits, percent     36.00%   36.00%  
Federal statutory income tax rate 35.00%   35.00% 35.00% 35.00%  
Total amount of unrecognized tax benefits           $ 56
Unrecognized tax benefits, net of related deferred tax assets           37
Favorable net impact to income tax expense due to recognition of tax benefits           $ 37