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Goodwill and Other Intangible Assets Goodwill Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Line Items]
Goodwill impairment loss		$ 0	$ 424
Goodwill		18,335	17,932	$ 18,178
Building Solutions EMEA/LA - Latin America
Goodwill [Line Items]
Goodwill, Impaired, Accumulated Impairment Loss				47
Building Solutions North America
Goodwill [Line Items]
Goodwill impairment loss			424
Building Solutions North America \| North America Retail [Member]
Goodwill [Line Items]
Goodwill		235
Building Technologies & Solutions \| Global Products
Goodwill [Line Items]
Goodwill impairment loss		0	0
Goodwill		5,859	5,579	5,547
Building Technologies & Solutions \| Building Solutions EMEA/LA
Goodwill [Line Items]
Goodwill impairment loss		0	0
Goodwill		2,021	1,967	1,849
Building Technologies & Solutions \| Building Solutions North America
Goodwill [Line Items]
Goodwill impairment loss	$ 424	0	424
Goodwill		$ 9,215	$ 9,160	$ 9,588