Significant Restructuring and Impairment Costs (Detail) $ in Millions	3 Months Ended				12 Months Ended				48 Months Ended
	Sep. 30, 2020 USD ($) Plant Employees	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Plant Employees	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2020 USD ($) Plant Employees
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 783	$ 235	$ 255
Number of employees to be severed | Employees									16,400
Restructuring and Related Cost, Number of Positions Eliminated, Inception to Date | Employees	12,700				12,700				12,700
Restructuring And Related Cost Expected Number Of Plants To Be Closed | Plant					9
Number Of Plants Closed | Plant	8				8				8
Goodwill, Impairment Loss	$ 0			$ 0	$ 424	0
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)	0		$ 62	0	$ 62
Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring And Related Cost Expected Number Of Plants To Be Closed | Plant					9
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 5		50
2020 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					297
Payments for Restructuring					(95)
Restructuring Reserve, Settled without Cash					(96)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					2
Restructuring Reserve	108				108				$ 108
2020 Restructuring Plan [Member] | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					196
Payments for Restructuring					(92)
Restructuring Reserve, Settled without Cash					0
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					2
Restructuring Reserve	106				106				106
2020 Restructuring Plan [Member] | Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					96
Payments for Restructuring					0
Restructuring Reserve, Settled without Cash					(96)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					0
Restructuring Reserve	0				0				0
2020 Restructuring Plan [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					5
Payments for Restructuring					(3)
Restructuring Reserve, Settled without Cash					0
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					0
Restructuring Reserve	2				2				2
2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							263
Payments for Restructuring					(69)	(67)	(47)
Restructuring Reserve, Settled without Cash							(42)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					1	(1)
Restructuring Reserve	30			102	30	102	174		30
2018 Restructuring Plan [Member] | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					(4)
2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							255
2018 Restructuring Plan [Member] | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							209
Payments for Restructuring					(69)	(61)	(45)
Restructuring Reserve, Settled without Cash							0
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					1	(1)
Restructuring Reserve	30			98	30	98	164		30
2018 Restructuring Plan [Member] | Employee Severance | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					0
2018 Restructuring Plan [Member] | Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							42
Payments for Restructuring					0	0	0
Restructuring Reserve, Settled without Cash							(42)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					0	0
Restructuring Reserve	0			0	0	0	0		0
2018 Restructuring Plan [Member] | Fixed Asset Impairment | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					0
2018 Restructuring Plan [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							12
Payments for Restructuring					0	(6)	(2)
Restructuring Reserve, Settled without Cash							0
Restructuring Reserve, Foreign Currency Translation Gain (Loss)					0	0
Restructuring Reserve	0			4	0	4	10		0
2018 Restructuring Plan [Member] | Other Restructuring [Member] | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					(4)
2018 Restructuring Plan [Member] | Power Solutions | Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							8
2018 Restructuring Plan [Member] | Power Solutions | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						(4)
2018 Restructuring Plan [Member] | Power Solutions | Employee Severance | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						(4)
2018 Restructuring Plan [Member] | Power Solutions | Fixed Asset Impairment | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						0
2018 Restructuring Plan [Member] | Power Solutions | Other Restructuring [Member] | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						0
2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								$ 367
Payments for Restructuring					(50)	(13)	(158)	(75)
Restructuring Reserve, Settled without Cash								(78)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)						(3)	(1)
Adjustment to restructuring reserves								25
Restructuring Reserve	6			61	6	61	80	239	6
2017 Restructuring Plan [Member] | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					5
2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								347
2017 Restructuring Plan [Member] | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								276
Payments for Restructuring					(50)	(11)	(152)	(75)
Restructuring Reserve, Settled without Cash								0
Restructuring Reserve, Foreign Currency Translation Gain (Loss)						(3)	(1)
Adjustment to restructuring reserves								25
Restructuring Reserve	6			56	6	56	73	226	6
2017 Restructuring Plan [Member] | Employee Severance | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					0
2017 Restructuring Plan [Member] | Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								77
Payments for Restructuring					0	0	0	0
Restructuring Reserve, Settled without Cash								(77)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)						0	0
Adjustment to restructuring reserves								0
Restructuring Reserve	0			0	0	0	0	0	0
2017 Restructuring Plan [Member] | Fixed Asset Impairment | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					0
2017 Restructuring Plan [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								14
Payments for Restructuring					0	(2)	(6)	0
Restructuring Reserve, Settled without Cash								(1)
Restructuring Reserve, Foreign Currency Translation Gain (Loss)						0	0
Adjustment to restructuring reserves								0
Restructuring Reserve	$ 0			$ 5	0	5	7	13	$ 0
2017 Restructuring Plan [Member] | Other Restructuring [Member] | Adoption of ASC 842
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment					5
2017 Restructuring Plan [Member] | Power Solutions | Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								20
2017 Restructuring Plan [Member] | Power Solutions | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						(3)
2017 Restructuring Plan [Member] | Power Solutions | Employee Severance | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						(3)
2017 Restructuring Plan [Member] | Power Solutions | Fixed Asset Impairment | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						0
2017 Restructuring Plan [Member] | Power Solutions | Other Restructuring [Member] | Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash						0
Building Solutions Asia Pacific | Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					56		16
Goodwill, Impairment Loss					0	0
Building Solutions Asia Pacific | 2020 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					49
Building Solutions Asia Pacific | 2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							16
Building Solutions Asia Pacific | 2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								16
Corporate | 2020 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					5
Corporate | 2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							50
Corporate | 2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								166
Building Solutions EMEA/LA | Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					59		56
Goodwill, Impairment Loss					0	0
Building Solutions EMEA/LA | 2020 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					43
Building Solutions EMEA/LA | 2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							56
Building Solutions EMEA/LA | 2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								74
Building Solutions North America
Restructuring Cost and Reserve [Line Items]
Goodwill, Impairment Loss					424
Building Solutions North America | Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					520		20
Goodwill, Impairment Loss		$ 424			424	0
Building Solutions North America | 2020 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					64
Building Solutions North America | 2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							20
Building Solutions North America | 2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								59
Global Products | Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					143	235	113
Goodwill, Impairment Loss					0	$ 0
Global Products | 2020 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 136
Global Products | 2018 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							$ 113
Global Products | 2017 Restructuring Plan [Member] | Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								$ 32