Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 25, 2020	Jan. 26, 2019	Jan. 25, 2020	Jan. 26, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 12,005	$ 12,446	$ 25,164	$ 25,518
Discontinued operations, held-for-sale | Service Provider Video
Disaggregation of Revenue [Line Items]
Revenue				168
Product
Disaggregation of Revenue [Line Items]
Revenue	8,671	9,273	18,549	19,163
Infrastructure Platforms
Disaggregation of Revenue [Line Items]
Revenue	6,528	7,102	14,067	14,724
Applications
Disaggregation of Revenue [Line Items]
Revenue	1,349	1,465	2,847	2,884
Security
Disaggregation of Revenue [Line Items]
Revenue	748	684	1,563	1,354
Other Products
Disaggregation of Revenue [Line Items]
Revenue	46	22	72	200
Other Products | Discontinued operations, held-for-sale | Service Provider Video
Disaggregation of Revenue [Line Items]
Revenue				168
Service
Disaggregation of Revenue [Line Items]
Revenue	$ 3,334	$ 3,173	$ 6,615	$ 6,355