Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 19,894	$ 19,748
Accumulated Amortization	6,692	5,981
Unamortized intangible assets	46	46
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	2	2
Acquired in-process research and development
Finite And Indefinite Lived Intangible Assets [Line Items]
Unamortized intangible assets	44	44
Developed technology
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	14,184	14,105
Accumulated Amortization	4,474	3,959
Customer relationships
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,651	4,616
Accumulated Amortization	1,674	1,509
Product rights
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	125	119
Accumulated Amortization	81	73
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	408	408
Accumulated Amortization	129	120
Patents and other
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	526	500
Accumulated Amortization	$ 334	$ 320