Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 20,447
Beginning balance				920
Beginning balance				21,367
Foreign currency translation adjustments	$ (614)	$ 285		(331)	$ (166)
Realized and unrealized gains (losses) on derivatives	1	(9)		(10)	(13)
Realized and unrealized gains (losses) on marketable securities	0	(3)		(2)	6
Other comprehensive income (loss)	(613)	273		(343)	(173)
Comprehensive income (loss) attributable to Johnson Controls	169	813		1,056	579
Comprehensive income attributable to noncontrolling interests	22	89		159	140
Total comprehensive income (loss)	191	902		1,215	719
Repurchase of ordinary shares	(56)	(307)		(255)	(426)
Ending balance	20,773			20,773
Ending balance	1,036			1,036
Ending balance	21,809			21,809
Net income attributable to Johnson Controls	723	555		1,391	736
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	20,874	19,388	$ 24,118	20,447	24,118
Foreign currency translation adjustments	(557)	268			(150)
Realized and unrealized gains (losses) on derivatives	3	(7)			(13)
Realized and unrealized gains (losses) on marketable securities	0	(3)			6
Other comprehensive income (loss)	(554)	258		(335)	(157)
Comprehensive income (loss) attributable to Johnson Controls	169	813		1,056	579
Cash dividends - ordinary shares	(240)	(234)		(722)	(705)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				0	0
Repurchase of ordinary shares	(56)	(307)		(255)	(426)
Change In noncontrolling interest share	0	0		0	0
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				179	0
Spin-off of Adient			(4,020)	0	(4,038)
Other, including options exercised	26	71		68	203
Ending balance	20,773	19,731		20,773	19,731
Net income attributable to Johnson Controls	723	555		1,391	736
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,006	813	972	920	972
Income attributable to noncontrolling interests	71	66		132	127
Foreign currency translation adjustments	(44)	3		3	(22)
Realized and unrealized gains on derivatives	(1)	(1)		1	1
Realized and unrealized gains on marketable securities	0	0		0	0
Other comprehensive income (loss)	(45)	2		4	(21)
Comprehensive income attributable to noncontrolling interests	26	68		136	106
Cash dividends - ordinary shares	0	0		0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(43)	(47)
Repurchase of ordinary shares	0	0		0	0
Change In noncontrolling interest share	4	3		23	(9)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				0	0
Spin-off of Adient				0	(138)
Other, including options exercised	0	0		0	0
Ending balance	1,036	884		1,036	884
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21,880	20,201	$ 25,090	21,367	25,090
Net income	794	621		1,523	863
Foreign currency translation adjustments	(601)	271		(328)	(172)
Realized and unrealized gains (losses) on derivatives	2	(8)		(1)	(12)
Realized and unrealized gains (losses) on marketable securities	0	(3)		(2)	6
Other comprehensive income (loss)	(599)	260		(331)	(178)
Total comprehensive income (loss)	195	881		1,192	685
Cash dividends - ordinary shares	(240)	(234)		(722)	(705)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(43)	(47)
Repurchase of ordinary shares	(56)	(307)		(255)	(426)
Change In noncontrolling interest share	4	3		(23)	9
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				179	0
Spin-off of Adient				0	4,176
Other, including options exercised	26	71		(68)	(203)
Ending balance	$ 21,809	$ 20,615		21,809	$ 20,615
Parent Company [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustments				(331)
Realized and unrealized gains (losses) on derivatives				(2)
Realized and unrealized gains (losses) on marketable securities				$ (2)