Shareholders' Equity (Stock Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Jan. 28, 2017	Jul. 30, 2016
Shares Repurchased
Cumulative Shares Repurchased, Beginning balance (in shares)	4,591
Repurchase of common stock under the stock repurchase program, Shares Repurchased (in shares)	65
Cumulative Shares Repurchased, Ending balance (in shares)	4,656
Weighted- Average Price per Share
Cumulative Weighted-Average Price per Share, Beginning balance (in dollars per share)	$ 21.04
Repurchase of common stock under the stock repurchase program, Weighted-Average Price per Share (in dollars per share)	30.72
Cumulative Weighted-Average Price per Share, Ending balance (in dollars per share)	$ 21.17
Amount Repurchased
Cumulative Amount Repurchased, Beginning balance	$ 96,597
Repurchase of common stock under the stock repurchase program, Amount Repurchased	2,002
Cumulative Amount Repurchased, Ending balance	98,599
Stock repurchase program
Class of Stock [Line Items]
Stock repurchases pending settlement	$ 56	$ 45