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Stock-based Compensation Summary of Stock-based Compensation Expense (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jan. 29, 2017
Jan. 31, 2016
Jan. 29, 2017
Jan. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Pre-tax stock-based compensation expense $ 18 $ 21 $ 32 $ 34
Tax-related benefits $ 7 $ 8 $ 12 $ 13