Revenue Recognition (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Oct. 01, 2018	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue, Net	$ 6,451,000,000	$ 6,282,000,000	$ 17,694,000,000	$ 17,217,000,000
Deferred revenue	(1,389,000,000)		(1,389,000,000)			$ (1,326,000,000)
Contract with Customer Asset Liability Net	(1,000,000)		(1,000,000)		$ (102,000,000)
Contract with Customer, Liability, Revenue Recognized	130,000,000		1,056,000,000
Revenue, Remaining Performance Obligation, Amount	$ 14,200,000,000		$ 14,200,000,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Explanation	60.00%		60.00%
Capitalized Contract Cost, Gross	$ 190,000,000		$ 190,000,000
Capitalized Contract Cost, Amortization	50,000,000		119,000,000
Capitalized Contract Cost, Impairment Loss			0
Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	4,896,000,000		13,058,000,000
Services [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	1,555,000,000		4,636,000,000
Building Solutions North America
Disaggregation of Revenue [Line Items]
Revenue, Net	2,327,000,000		6,630,000,000
Building Solutions North America | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	1,494,000,000		4,202,000,000
Building Solutions North America | Services [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	833,000,000		2,428,000,000
Building Solutions EMEA/LA
Disaggregation of Revenue [Line Items]
Revenue, Net	922,000,000		2,707,000,000
Building Solutions EMEA/LA | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	464,000,000		1,297,000,000
Building Solutions EMEA/LA | Services [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	458,000,000		1,410,000,000
Building Solutions Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue, Net	691,000,000		1,932,000,000
Building Solutions Asia Pacific | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	427,000,000		1,134,000,000
Building Solutions Asia Pacific | Services [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	264,000,000		798,000,000
Global Products
Disaggregation of Revenue [Line Items]
Revenue, Net	2,511,000,000		6,425,000,000
Global Products | Global Products- Building Management [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	342,000,000		943,000,000
Global Products | Global Products- HVAC & Refrigeration Equipment [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	1,869,000,000		4,628,000,000
Global Products | Global Products- Specialty [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	300,000,000		854,000,000
Global Products | Products and Systems [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	2,511,000,000		6,425,000,000
Global Products | Services [Domain]
Disaggregation of Revenue [Line Items]
Revenue, Net	0		0
Other Current Assets
Disaggregation of Revenue [Line Items]
Capitalized Contract Cost, Gross	100,000,000		100,000,000
Accounts Receivable [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Current	1,428,000,000		1,428,000,000		1,261,000,000
Other Noncurrent Assets
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net, Noncurrent	85,000,000		85,000,000		85,000,000
Capitalized Contract Cost, Gross	90,000,000		90,000,000
Deferred Revenue [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue	(1,389,000,000)		(1,389,000,000)		(1,335,000,000)
Other Noncurrent Liabilities [Member]
Disaggregation of Revenue [Line Items]
Contract with Customer, Liability, Noncurrent	$ (125,000,000)		$ (125,000,000)		$ (113,000,000)