Acquisitions and Divestitures (Summary Of Allocation Of Total Purchase Consideration) (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 25, 2015	Jul. 26, 2014	Jul. 27, 2013
Business Acquisition [Line Items]
Purchase Consideration	$ 334	$ 3,181	$ 6,982
Net Tangible Assets Acquired (Liabilities Assumed)	(20)	25	(322)
Purchased Intangible Assets	99	838	2,391
Goodwill	255	2,318	4,913
Metacloud
Business Acquisition [Line Items]
Purchase Consideration	149
Net Tangible Assets Acquired (Liabilities Assumed)	(7)
Purchased Intangible Assets	29
Goodwill	127
Composite Software
Business Acquisition [Line Items]
Purchase Consideration		160
Net Tangible Assets Acquired (Liabilities Assumed)		(10)
Purchased Intangible Assets		75
Goodwill		95
Sourcefire, Inc.
Business Acquisition [Line Items]
Purchase Consideration		2,449
Net Tangible Assets Acquired (Liabilities Assumed)		81
Purchased Intangible Assets		577
Goodwill		1,791
WhipTail
Business Acquisition [Line Items]
Purchase Consideration		351
Net Tangible Assets Acquired (Liabilities Assumed)		(34)
Purchased Intangible Assets		105
Goodwill		280
Tail-f
Business Acquisition [Line Items]
Purchase Consideration		167
Net Tangible Assets Acquired (Liabilities Assumed)		(7)
Purchased Intangible Assets		61
Goodwill		113
NDS
Business Acquisition [Line Items]
Purchase Consideration			5,005
Net Tangible Assets Acquired (Liabilities Assumed)			(185)
Purchased Intangible Assets			1,746
Goodwill			3,444
Meraki
Business Acquisition [Line Items]
Purchase Consideration			974
Net Tangible Assets Acquired (Liabilities Assumed)			(59)
Purchased Intangible Assets			289
Goodwill			744
Intucell
Business Acquisition [Line Items]
Purchase Consideration			360
Net Tangible Assets Acquired (Liabilities Assumed)			(23)
Purchased Intangible Assets			106
Goodwill			277
Ubiquisys
Business Acquisition [Line Items]
Purchase Consideration			280
Net Tangible Assets Acquired (Liabilities Assumed)			(30)
Purchased Intangible Assets			123
Goodwill			187
All others
Business Acquisition [Line Items]
Purchase Consideration	185	54	363
Net Tangible Assets Acquired (Liabilities Assumed)	(13)	(5)	(25)
Purchased Intangible Assets	70	20	127
Goodwill	$ 128	$ 39	$ 261