Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Oct. 26, 2019	Oct. 27, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 13,159	$ 13,072
Discontinued operations, held-for-sale | Service Provider Video
Disaggregation of Revenue [Line Items]
Revenue		168
Product
Disaggregation of Revenue [Line Items]
Revenue	9,878	9,890
Infrastructure Platforms
Disaggregation of Revenue [Line Items]
Revenue	7,538	7,622
Applications
Disaggregation of Revenue [Line Items]
Revenue	1,499	1,419
Security
Disaggregation of Revenue [Line Items]
Revenue	815	670
Other Products
Disaggregation of Revenue [Line Items]
Revenue	26	178
Other Products | Discontinued operations, held-for-sale | Service Provider Video
Disaggregation of Revenue [Line Items]
Revenue	168
Service
Disaggregation of Revenue [Line Items]
Revenue	$ 3,281	$ 3,182