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Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Jan. 31, 2016
Apr. 30, 2017
Apr. 30, 2016
Jul. 31, 2016
Income Tax Disclosure [Abstract]            
Discrete tax benefit due to changes in federal tax law     $ 12      
Effective tax rate 33.00% 34.00%   31.00% 33.00%  
Effective income tax rate reconciliation, excluding discrete tax benefits, percent 34.00%     34.00%    
Federal statutory income tax rate 35.00% 35.00%   35.00% 35.00%  
Total amount of unrecognized tax benefits           $ 60
Unrecognized tax benefits, net of related deferred tax assets           40
Favorable net impact to income tax expense due to recognition of tax benefits           $ 40