Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Apr. 25, 2020	Apr. 27, 2019	Apr. 25, 2020	Apr. 27, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 11,983	$ 12,958	$ 37,147	$ 38,476
Discontinued operations, held-for-sale | Service Provider Video
Disaggregation of Revenue [Line Items]
Revenue				168
Product
Disaggregation of Revenue [Line Items]
Revenue	8,597	9,722	27,146	28,885
Infrastructure Platforms
Disaggregation of Revenue [Line Items]
Revenue	6,429	7,523	20,496	22,247
Applications
Disaggregation of Revenue [Line Items]
Revenue	1,363	1,431	4,211	4,315
Security
Disaggregation of Revenue [Line Items]
Revenue	776	729	2,340	2,083
Other Products
Disaggregation of Revenue [Line Items]
Revenue	28	39	100	239
Service
Disaggregation of Revenue [Line Items]
Revenue	$ 3,386	$ 3,236	$ 10,001	$ 9,591