Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 20,447
Beginning balance				920
Beginning balance				21,367
Foreign currency translation adjustments	$ 204	$ 252		283	$ (451)
Realized and unrealized gains (losses) on derivatives	(10)	(8)		(11)	(4)
Realized and unrealized gains (losses) on marketable securities	(2)	11		(2)	9
Other comprehensive income (loss)	192	255		270	(446)
Comprehensive income (loss) attributable to Johnson Controls	598	98		887	(234)
Comprehensive income attributable to noncontrolling interests	77	42		137	51
Total comprehensive income (loss)	675	140		1,024	(183)
Repurchase of ordinary shares	(49)	(119)		(199)	(119)
Ending balance	20,874			20,874
Ending balance	1,006			1,006
Ending balance	21,880			21,880
Net income attributable to Johnson Controls	438	(148)		668	181
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	20,535	19,577	$ 24,118	20,447	24,118
Foreign currency translation adjustments	168	241			(418)
Realized and unrealized gains (losses) on derivatives	(6)	(6)			(6)
Realized and unrealized gains (losses) on marketable securities	(2)	11			9
Other comprehensive income (loss)	160	246		219	(415)
Comprehensive income (loss) attributable to Johnson Controls	598	98		887	(234)
Cash dividends - ordinary shares	(240)	(235)		(482)	(471)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	0	0		0	0
Repurchase of ordinary shares	(49)	(119)		(199)	(119)
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	0	(18)	(4,020)	0	4,038
Other, including options exercised	30	85		(42)	(132)
Ending balance	20,874	19,388	19,577	20,874	19,388
Net income attributable to Johnson Controls	438	(148)		668	181
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	965	819	972	920	972
Income attributable to noncontrolling interests	33	25		61	61
Foreign currency translation adjustments	31	10		47	(25)
Realized and unrealized gains on derivatives	1	(2)		2	2
Realized and unrealized gains on marketable securities	0	0		0	0
Other comprehensive income (loss)	32	8		49	(23)
Comprehensive income attributable to noncontrolling interests	65	33		110	38
Cash dividends - ordinary shares	0	0		0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(43)	(47)		(43)	(47)
Repurchase of ordinary shares	0	0		0	0
Change In noncontrolling interest share	19	8		(19)	12
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				0	0
Spin-off of Adient	0	0		0	138
Other, including options exercised	0	0		0	0
Ending balance	1,006	813	819	1,006	813
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21,500	20,396	25,090	21,367	25,090
Net income	471	(123)		729	242
Foreign currency translation adjustments	199	251		273	(443)
Realized and unrealized gains (losses) on derivatives	(5)	(8)		(3)	(4)
Realized and unrealized gains (losses) on marketable securities	(2)	11		(2)	9
Other comprehensive income (loss)	192	254		268	(438)
Total comprehensive income (loss)	663	131		997	(196)
Cash dividends - ordinary shares	(240)	(235)		(482)	(471)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(43)	(47)		(43)	(47)
Repurchase of ordinary shares	(49)	(119)		(199)	(119)
Change In noncontrolling interest share	19	8		(19)	12
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				179	0
Spin-off of Adient	0	(18)		0	4,176
Other, including options exercised	30	85		(42)	(132)
Ending balance	21,880	20,201	$ 20,396	21,880	20,201
Parent Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				20,447
Beginning balance				0
Beginning balance				20,447
Foreign currency translation adjustments	168	241			(418)
Realized and unrealized gains (losses) on derivatives	(6)	(6)			(6)
Realized and unrealized gains (losses) on marketable securities	(2)	11			9
Other comprehensive income (loss)	160	246		219	(415)
Comprehensive income (loss) attributable to Johnson Controls	598	98		887	(234)
Comprehensive income attributable to noncontrolling interests	0	0		0	0
Total comprehensive income (loss)	598	98		887	(234)
Ending balance	20,874			20,874
Ending balance	0			0
Ending balance	20,874			20,874
Net income attributable to Johnson Controls	$ 438	$ (148)		668	$ 181
Parent Company [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustments				226
Realized and unrealized gains (losses) on derivatives				(5)
Realized and unrealized gains (losses) on marketable securities				$ (2)