Revenue Recognition (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 22,317,000,000	$ 23,968,000,000	$ 23,400,000,000
Contract with Customer, Liability, Current	(1,435,000,000)	(1,407,000,000)
Contract with Customer Asset Liability Net	(181,000,000)	(156,000,000)
Contract with Customer, Liability, Revenue Recognized	1,300,000,000	1,200,000,000
Revenue, Remaining Performance Obligation, Amount	$ 14,400,000,000
Remaining Performance Obligations Expected as Revenue Over the Next Two Years	60.00%
Capitalized Contract Cost, Gross	$ 223,000,000	212,000,000
Capitalized Contract Cost, Amortization	162,000,000	157,000,000
Capitalized Contract Cost, Impairment Loss	0	0
Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	16,253,000,000	17,711,000,000
Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	6,064,000,000	6,257,000,000
Building Solutions North America
Disaggregation of Revenue [Line Items]
Net sales	8,605,000,000	9,031,000,000
Building Solutions North America | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	5,371,000,000	5,745,000,000
Building Solutions North America | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	3,234,000,000	3,286,000,000
Building Solutions EMEA/LA
Disaggregation of Revenue [Line Items]
Net sales	3,440,000,000	3,655,000,000
Building Solutions EMEA/LA | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,644,000,000	1,767,000,000
Building Solutions EMEA/LA | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,796,000,000	1,888,000,000
Building Solutions Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales	2,403,000,000	2,658,000,000
Building Solutions Asia Pacific | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,369,000,000	1,575,000,000
Building Solutions Asia Pacific | Services [Domain]
Disaggregation of Revenue [Line Items]
Net sales	1,034,000,000	1,083,000,000
Global Products
Disaggregation of Revenue [Line Items]
Net sales	7,869,000,000	8,624,000,000
Global Products | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Net sales	7,869,000,000	8,624,000,000
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	1,205,000,000	1,292,000,000
Global Products | HVAC & refrigeration equipment
Disaggregation of Revenue [Line Items]
Net sales	5,613,000,000	6,181,000,000
Global Products | Specialty products
Disaggregation of Revenue [Line Items]
Net sales	1,051,000,000	1,151,000,000
Other current assets
Disaggregation of Revenue [Line Items]
Capitalized Contract Cost, Gross	119,000,000	110,000,000
Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Current	1,395,000,000	1,389,000,000
Other noncurrent assets
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Noncurrent	104,000,000	90,000,000
Capitalized Contract Cost, Gross	104,000,000	102,000,000
Deferred Revenue [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Current	(1,435,000,000)	(1,407,000,000)
Other Noncurrent Liabilities [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Noncurrent	$ (245,000,000)	$ (228,000,000)