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Investments (Realized Net Gains (Losses) Related to Available-for-Sale Investments) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Apr. 28, 2018
Apr. 29, 2017
Apr. 28, 2018
Apr. 29, 2017
Schedule of Investments [Line Items]        
Total $ 17 $ (76) $ 108 $ (91)
Net gains (losses) on investments in publicly traded equity securities        
Schedule of Investments [Line Items]        
Total 56 (59) 239 (50)
Net gains (losses) on investments in fixed income securities        
Schedule of Investments [Line Items]        
Total $ (39) $ (17) $ (131) $ (41)