Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 19,495	$ 19,475
Accumulated Amortization	3,822	3,073
Unamortized intangible assets	33	39
Acquired in-process research and development
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	31	37
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	2	2
Developed technology
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,976	13,966
Accumulated Amortization	2,352	1,782
Customer relationships
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,586	4,584
Accumulated Amortization	1,022	861
Product rights
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	118	121
Accumulated Amortization	60	58
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	407	407
Accumulated Amortization	93	84
Patents and other
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	407	397
Accumulated Amortization	$ 295	$ 288