Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 19,597	$ 19,530
Accumulated Amortization	5,271	4,555
Unamortized intangible assets	48	3
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	2	2
Acquired in-process research and development (a)
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	46	1
Developed technology
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,985	13,960
Accumulated Amortization	3,440	2,906
Customer relationships
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,606	4,608
Accumulated Amortization	1,345	1,183
Product rights
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	106	110
Accumulated Amortization	61	60
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	407	407
Accumulated Amortization	110	102
Patents and other
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	493	445
Accumulated Amortization	$ 315	$ 305