Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 19,860	$ 19,748
Accumulated Amortization	6,349	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	14,164	14,105
Accumulated Amortization	4,223	3,959
Customer relationships
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,645	4,616
Accumulated Amortization	1,592	1,509
Product rights
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	128	119
Accumulated Amortization	80	73
Trademarks
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	408	408
Accumulated Amortization	125	120
Patents and other
Finite And Indefinite Lived Intangible Assets [Line Items]
Gross Carrying Amount	515	500
Accumulated Amortization	$ 329	$ 320