Acquisitions and Divestitures - Summary of Allocation of Total Purchase Consideration (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 27, 2019	Jul. 28, 2018	Jul. 29, 2017
Business Acquisition [Line Items]
Purchase Consideration	$ 2,686	$ 3,218	$ 3,600
Net Tangible Assets Acquired (Liabilities Assumed)	(74)	334
Purchased Intangible Assets	672	867
Goodwill	2,088	2,017
Duo
Business Acquisition [Line Items]
Purchase Consideration	2,025
Net Tangible Assets Acquired (Liabilities Assumed)	(57)
Purchased Intangible Assets	342
Goodwill	1,740
Luxtera
Business Acquisition [Line Items]
Purchase Consideration	596
Net Tangible Assets Acquired (Liabilities Assumed)	(19)
Purchased Intangible Assets	319
Goodwill	296
Viptela
Business Acquisition [Line Items]
Purchase Consideration		497
Net Tangible Assets Acquired (Liabilities Assumed)		(18)
Purchased Intangible Assets		180
Goodwill		335
Springpath
Business Acquisition [Line Items]
Purchase Consideration		248
Net Tangible Assets Acquired (Liabilities Assumed)		(11)
Purchased Intangible Assets		160
Goodwill		99
BroadSoft
Business Acquisition [Line Items]
Purchase Consideration		2,179
Net Tangible Assets Acquired (Liabilities Assumed)		353
Purchased Intangible Assets		430
Goodwill		1,396
Accompany
Business Acquisition [Line Items]
Purchase Consideration		222
Net Tangible Assets Acquired (Liabilities Assumed)		6
Purchased Intangible Assets		55
Goodwill		161
Others
Business Acquisition [Line Items]
Purchase Consideration	65	72
Net Tangible Assets Acquired (Liabilities Assumed)	2	4
Purchased Intangible Assets	11	42
Goodwill	$ 52	$ 26