Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Millions	6 Months Ended
Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 18,381
Business Acquisitions	9
Business Divestitures	(1)
Currency Translation and Other	(78)
Ending Balance	18,311
Building Technologies & Solutions \| Building Solutions North America
Goodwill [Roll Forward]
Beginning Balance	9,603
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(22)
Ending Balance	9,581
Building Technologies & Solutions \| Building Solutions EMEA/LA
Goodwill [Roll Forward]
Beginning Balance	1,950
Business Acquisitions	0
Business Divestitures	(1)
Currency Translation and Other	(36)
Ending Balance	1,913
Building Technologies & Solutions \| Building Solutions Asia Pacific
Goodwill [Roll Forward]
Beginning Balance	1,235
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	4
Ending Balance	1,239
Building Technologies & Solutions \| Global Products
Goodwill [Roll Forward]
Beginning Balance	5,593
Business Acquisitions	9
Business Divestitures	0
Currency Translation and Other	(24)
Ending Balance	$ 5,578

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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