Goodwill and Intangible Assets - Intangibles (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015	Oct. 31, 2015
Intangible assets
Intangible assets, gross	$ 9,085		$ 9,085		$ 9,717
Amortizable intangible assets, accumulated amortization	(4,771)		(4,771)		(4,684)
Finite-lived Intangible Assets, Accumulated Impairment Losses			(3,103)		(3,103)
Total Intangible Assets- Net	1,211		1,211		1,930
Amortizable intangible assets, net	1,211		1,211
Goodwill adjustments/reclassifications			478
Amount of fully amortized intangible assets			164
Amortization of intangible assets	210	$ 225	629	$ 632
Trilead Ag
Intangible assets
Adjustments			11
In-process research and development
Intangible assets
Amortizable intangible assets, gross	0		0		159
Amortizable intangible assets, accumulated amortization	0		0		0
Finite-lived Intangible Assets, Accumulated Impairment Losses			0		0
Amortizable intangible assets, net	0		0		159
Customer contracts, customer lists and distribution agreements
Intangible assets
Amortizable intangible assets, gross	4,648		4,648		5,109
Amortizable intangible assets, accumulated amortization	(3,525)		(3,525)		(3,517)
Finite-lived Intangible Assets, Accumulated Impairment Losses			(856)		(856)
Amortizable intangible assets, net	267		267		736
Developed and core technology and patents
Intangible assets
Amortizable intangible assets, gross	4,218		4,218		4,218
Amortizable intangible assets, accumulated amortization	(1,187)		(1,187)		(1,110)
Finite-lived Intangible Assets, Accumulated Impairment Losses			(2,138)		(2,138)
Amortizable intangible assets, net	893		893		970
Developed and core technology and patents | In-process research and development
Intangible assets
Reclassified assets	159		159
Trade name and trademarks
Intangible assets
Amortizable intangible assets, gross	219		219		231
Amortizable intangible assets, accumulated amortization	(59)		(59)		(57)
Finite-lived Intangible Assets, Accumulated Impairment Losses			(109)		(109)
Amortizable intangible assets, net	$ 51		$ 51		$ 65