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Stock-based Compensation Summary of Stock-based Compensation Expense (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jan. 28, 2018
Jan. 29, 2017
Jan. 28, 2018
Jan. 29, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Total pre-tax stock-based compensation expense $ 18 $ 18 $ 32 $ 32
Tax-related benefits $ 2 $ 7 $ 7 $ 12