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Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2024	Mar. 31, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Goodwill [Roll Forward]
Goodwill				$ 17,737	$ 16,956
Accumulated impairment loss				(965)	(781)
Beginning Balance			$ 16,772	16,175
Acquisitions				586
Impairments		$ (230)	(230)	(184)
Foreign currency translation and other			183	195
Ending Balance	$ 16,725		16,725	16,772	16,175
Disposal Group, Held-for-sale, Not Discontinued Operations \| Air Distribution Technologies
Goodwill [Roll Forward]
Impairments	(21)
Building Solutions North America
Goodwill [Roll Forward]
Goodwill				10,040	9,630
Accumulated impairment loss				(659)	(659)
Beginning Balance			9,381	8,971
Acquisitions				399
Impairments			0	0
Foreign currency translation and other			10	11
Ending Balance	9,391		9,391	9,381	8,971
Building Solutions EMEA/LA
Goodwill [Roll Forward]
Goodwill				1,932	1,794
Accumulated impairment loss				(47)	(47)
Beginning Balance			1,885	1,747
Acquisitions				13
Impairments			(230)	0
Foreign currency translation and other			107	125
Ending Balance	1,762		1,762	1,885	1,747
Building Solutions Asia Pacific
Goodwill [Roll Forward]
Goodwill				1,179	1,116
Accumulated impairment loss				0	0
Beginning Balance			1,179	1,116
Acquisitions				55
Impairments			0	0
Foreign currency translation and other			48	8
Ending Balance	1,227		1,227	1,179	1,116
Global Products
Goodwill [Roll Forward]
Goodwill				4,586	4,416
Accumulated impairment loss				(259)	(75)
Beginning Balance			4,327	4,341
Acquisitions				119
Impairments			0	(184)
Foreign currency translation and other			18	51
Ending Balance	$ 4,345		$ 4,345	$ 4,327	$ 4,341