Acquisitions and Divestitures (Additional Information Acquisitions) (Details) $ in Millions	3 Months Ended			6 Months Ended
	Apr. 30, 2016 USD ($)	Jan. 23, 2016	Oct. 24, 2015	Jan. 23, 2016 USD ($) acquisitions	Jan. 24, 2015 USD ($)
Supplementary Information [Line Items]
Number of business combinations (in numbers) | acquisitions				7
Number of business combinations in Other (in numbers) | acquisitions				7
Acquired Cash and Cash Equivalents				$ 10
Purchase Consideration				1,168
General and administrative
Supplementary Information [Line Items]
Business Combination, Acquisition Related Costs				14	$ 5
MaintenanceNet
Supplementary Information [Line Items]
Business Acquisition, Effective Date of Acquisition			Aug. 06, 2015
Purchase Consideration				105
OpenDNS
Supplementary Information [Line Items]
Business Acquisition, Effective Date of Acquisition			Aug. 26, 2015
Purchase Consideration				545
Lancope
Supplementary Information [Line Items]
Business Acquisition, Effective Date of Acquisition		Dec. 21, 2015
Purchase Consideration				$ 410
Subsequent Event | Acano
Supplementary Information [Line Items]
Business Acquisition, Effective Date of Acquisition	Jan. 29, 2016
Purchase Consideration	$ 550
Subsequent Event | Jasper
Supplementary Information [Line Items]
Business Acquisition, Date of announcement	Feb. 03, 2016
Purchase Consideration	$ 1,400