Revenue Recognition (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Net sales	$ 23,668,000,000	$ 22,317,000,000	$ 23,968,000,000
Contract with Customer, Liability, Current	(1,637,000,000)	(1,435,000,000)
Contract with Customer Asset Liability Net	(89,000,000)	(181,000,000)
Contract with Customer, Liability, Revenue Recognized	1,200,000,000	1,300,000,000
Revenue, Remaining Performance Obligation, Amount	$ 16,100,000,000
Remaining Performance Obligations Expected as Revenue Over the Next Two Years	60.00%
Capitalized Contract Cost, Gross	$ 266,000,000	223,000,000
Capitalized Contract Cost, Amortization	173,000,000	162,000,000
Capitalized Contract Cost, Impairment Loss	0	0
Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	17,202,000,000	16,253,000,000
Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	6,466,000,000	6,064,000,000
Building Solutions North America
Disaggregation of Revenue [Line Items]
Net sales	8,685,000,000	8,605,000,000
Building Solutions North America | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	5,312,000,000	5,371,000,000
Building Solutions North America | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	3,373,000,000	3,234,000,000
Building Solutions EMEA/LA
Disaggregation of Revenue [Line Items]
Net sales	3,727,000,000	3,440,000,000
Building Solutions EMEA/LA | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,772,000,000	1,644,000,000
Building Solutions EMEA/LA | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,955,000,000	1,796,000,000
Building Solutions Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales	2,654,000,000	2,403,000,000
Building Solutions Asia Pacific | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,516,000,000	1,369,000,000
Building Solutions Asia Pacific | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,138,000,000	1,034,000,000
Global Products
Disaggregation of Revenue [Line Items]
Net sales	8,602,000,000	7,869,000,000
Global Products | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	8,602,000,000	7,869,000,000
Global Products | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	0	0
Global Products | Building management systems
Disaggregation of Revenue [Line Items]
Net sales	6,173,000,000	5,685,000,000
Global Products | HVAC & refrigeration equipment
Disaggregation of Revenue [Line Items]
Net sales	2,192,000,000	1,957,000,000
Global Products | Specialty products
Disaggregation of Revenue [Line Items]
Net sales	237,000,000	227,000,000
Other current assets
Disaggregation of Revenue [Line Items]
Capitalized Contract Cost, Gross	149,000,000	119,000,000
Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Current	1,718,000,000	1,395,000,000
Other noncurrent assets
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Noncurrent	99,000,000	104,000,000
Capitalized Contract Cost, Gross	117,000,000	104,000,000
Deferred Revenue [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Current	(1,637,000,000)	(1,435,000,000)
Other Noncurrent Liabilities
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Noncurrent	$ (269,000,000)	$ (245,000,000)