Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Sep. 30, 2023
Goodwill [Line Items]
Goodwill			$ 18,901
Accumulated impairment loss			(965)
Goodwill [Roll Forward]
Balance at September 30, 2023		$ 17,936
Impairments	$ (230)	(230)
Foreign currency translation and other (1)		51
Balance at March 31, 2024	17,757	17,757
Building Solutions North America
Goodwill [Line Items]
Goodwill			10,040
Accumulated impairment loss			(659)
Goodwill [Roll Forward]
Balance at September 30, 2023		9,381
Impairments		0
Foreign currency translation and other (1)		11
Balance at March 31, 2024	9,392	9,392
Building Solutions EMEA/LA
Goodwill [Line Items]
Goodwill			1,932
Accumulated impairment loss			(47)
Goodwill [Roll Forward]
Balance at September 30, 2023		1,885
Impairments		(230)
Foreign currency translation and other (1)		44
Balance at March 31, 2024	1,699	1,699
Building Solutions Asia Pacific
Goodwill [Line Items]
Goodwill			1,179
Accumulated impairment loss			0
Goodwill [Roll Forward]
Balance at September 30, 2023		1,179
Impairments		0
Foreign currency translation and other (1)		1
Balance at March 31, 2024	1,180	1,180
Global Products
Goodwill [Line Items]
Goodwill			5,750
Accumulated impairment loss			$ (259)
Goodwill [Roll Forward]
Balance at September 30, 2023		5,491
Impairments		0
Foreign currency translation and other (1)		(5)
Balance at March 31, 2024	$ 5,486	$ 5,486