Fair Value (Fair Value, Nonrecurring Measurement) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 26, 2019	Jan. 27, 2018	Jan. 26, 2019	Jan. 27, 2018
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Total gains (losses) for nonrecurring measurements	$ 12	$ 2	$ 6	$ (19)
Equity securities
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Total gains (losses) for nonrecurring measurements	12	(18)	6	(39)
Property held for sale—land and buildings
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Total gains (losses) for nonrecurring measurements	$ 0	$ 20	$ 0	$ 20