Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 18,084	$ 20,036	$ 19,766	$ 21,164
Beginning balance			1,063
Beginning balance			20,829
Net income (loss) attributable to Johnson Controls	(182)	4,192	190	5,062
Foreign currency translation adjustments	72	(90)	(148)	(103)
Foreign currency translation adjustments	76	(94)	(157)	(95)
Realized and unrealized gains (losses) on derivatives	6	(9)	3	10
Pension and postretirement plans	0	0	(1)	0
Other comprehensive income (loss)	82	(103)	(155)	(85)
Comprehensive income (loss) attributable to Johnson Controls	(104)	4,097	42	4,969
Comprehensive income attributable to noncontrolling interests	64	76	108	179
Total comprehensive income (loss)	(40)	4,173	150	5,148
Cash dividends - ordinary shares	(195)	(208)	(590)	(683)
Repurchases and retirements of ordinary shares		(4,122)	(1,467)	(5,122)
Repurchases of ordinary shares		(87)		(1,087)
Adoption of ASU	17,805	20,036	17,805	20,363
Adoption of ASU	1,068		1,063
Adoption of ASU	18,873		20,829
Other, including options exercised	20	77	59	143
Ending balance	17,805	20,363	17,805	20,363
Ending balance	1,068		1,068
Ending balance	18,873		18,873
Power Solutions
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Divestiture of Power Solutions		483		483
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	18,084	20,036	19,766	21,164
Net income (loss) attributable to Johnson Controls	(182)	4,192	190	5,062
Foreign currency translation adjustments	72	(90)	(148)	(103)
Realized and unrealized gains (losses) on derivatives	6	(5)	1	10
Pension and postretirement plans			(1)	0
Other comprehensive income (loss)	78	(95)	(148)	(93)
Comprehensive income (loss) attributable to Johnson Controls	(104)	4,097	42	4,969
Cash dividends - ordinary shares	(195)	(208)	(590)	(683)
Dividends attributable to noncontrolling interests			0	0
Repurchases and retirements of ordinary shares	0		(1,467)
Repurchases of ordinary shares		(4,122)		(5,122)
Divestiture of Power Solutions	0	483
Adoption of ASU	17,805	20,363	19,766	20,363
Other, including options exercised	20	77	59	143
Ending balance	17,805	20,363	17,805	20,363
Equity Attributable to Johnson Controls | Power Solutions
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Divestiture of Power Solutions			0	483
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,004	1,265	1,063	1,294
Income attributable to noncontrolling interests	60	84	115	171
Foreign currency translation adjustments	4	(4)	(9)	8
Realized and unrealized gains on derivatives	0	(4)	2	0
Pension and postretirement plans			0	0
Other comprehensive income (loss)	4	(8)	(7)	8
Comprehensive income attributable to noncontrolling interests	64	76	108	179
Cash dividends - ordinary shares	0	0	0	0
Dividends attributable to noncontrolling interests			(103)	(132)
Repurchases and retirements of ordinary shares	0		0
Repurchases of ordinary shares		0		0
Divestiture of Power Solutions	0	(295)
Adoption of ASU	1,068	1,046	1,063	1,294
Other, including options exercised	0	0	0	0
Ending balance	1,068	1,046	1,068	1,046
Equity Attributable to Noncontrolling Interest | Power Solutions
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Divestiture of Power Solutions			0	(295)
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	19,088	21,301	20,829	22,458
Net income	(122)	4,276	305	5,233
Foreign currency translation adjustments	76	(94)	(157)	(95)
Realized and unrealized gains (losses) on derivatives	6	(9)	3	10
Pension and postretirement plans			(1)	0
Other comprehensive income (loss)	82	(103)	(155)	(85)
Total comprehensive income (loss)	(40)	4,173	150	5,148
Cash dividends - ordinary shares	(195)	(208)	(590)	(683)
Dividends attributable to noncontrolling interests			(103)	(132)
Repurchases and retirements of ordinary shares	0		(1,467)
Repurchases of ordinary shares		(4,122)		(5,122)
Divestiture of Power Solutions	0	188
Adoption of ASU	18,873	21,409	18,873	22,458
Other, including options exercised	20	77	59	143
Ending balance	$ 18,873	$ 21,409	18,873	21,409
Total Equity Excluding Redeemable Noncontrolling Interest [Member] | Power Solutions
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Divestiture of Power Solutions			0	188
Adoption of ASC 606 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				(45)
Adoption of ASU				(45)
Adoption of ASC 606 | Equity Attributable to Johnson Controls | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	(45)
Adoption of ASU			0	(45)
Adoption of ASC 606 | Equity Attributable to Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	0
Adoption of ASU			0	0
Adoption of ASC 606 | Total Equity Excluding Redeemable Noncontrolling Interest [Member] | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	(45)
Adoption of ASU			0	(45)
Adoption of ASU 2016-16 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				(546)
Adoption of ASU				(546)
Adoption of ASU 2016-16 | Equity Attributable to Johnson Controls | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	(546)
Adoption of ASU			0	(546)
Adoption of ASU 2016-16 | Equity Attributable to Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	0
Adoption of ASU			0	0
Adoption of ASU 2016-16 | Total Equity Excluding Redeemable Noncontrolling Interest [Member] | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	(546)
Adoption of ASU			0	(546)
Adoption of ASC 842 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(5)
Adoption of ASU			(5)
Adoption of ASC 842 | Equity Attributable to Johnson Controls | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(5)	0
Adoption of ASU			(5)	0
Adoption of ASC 842 | Equity Attributable to Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	0
Adoption of ASU			0	0
Adoption of ASC 842 | Total Equity Excluding Redeemable Noncontrolling Interest [Member] | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(5)	0
Adoption of ASU			$ (5)	$ 0