Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 20,102	$ 21,164	$ 20,535	$ 21,164	$ 20,447
Beginning balance		1,294		1,294
Beginning balance		22,458		22,458
Net income (loss) attributable to Johnson Controls	515		438	870	668
Foreign currency translation adjustments	114		168
Foreign currency translation adjustments	117		204	(1)	283
Realized and unrealized gains (losses) on derivatives	17		(10)	19	(11)
Realized and unrealized losses on marketable securities	0		(2)	0	(2)
Other comprehensive income	134		192	18	270
Comprehensive income attributable to Johnson Controls	643		598	872	887
Comprehensive income attributable to noncontrolling interests	49		77	103	137
Total comprehensive income	692		675	975	1,024
Cash dividends - ordinary shares	(235)		(240)	(475)	(482)
Repurchase of ordinary shares	(533)		(49)	(1,000)	(199)
Other, including options exercised	59		30	66	42
Ending balance	20,036	20,102	20,874	20,036	20,874
Ending balance	1,265			1,265
Ending balance	21,301			21,301
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	20,102	21,164	20,535	21,164	20,447
Net income (loss) attributable to Johnson Controls	515		438	870	668
Foreign currency translation adjustments	114		168		226
Foreign currency translation adjustments				(13)
Realized and unrealized gains (losses) on derivatives	14		(6)	15	(5)
Realized and unrealized losses on marketable securities	0		(2)	0	(2)
Other comprehensive income (loss)	128		160	2	219
Comprehensive income attributable to Johnson Controls	643		598	872	887
Cash dividends - ordinary shares	(235)		(240)	(475)	(482)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	0		0	0	0
Repurchase of ordinary shares	(533)		(49)	(1,000)	(199)
Change In noncontrolling interest share	0		0	0	0
Other, including options exercised	59		30	66	42
Ending balance	20,036	20,102	20,874	20,036	20,874
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,305	1,294	965	1,294	920
Income attributable to noncontrolling interests	43		33	87	61
Foreign currency translation adjustments	3		31	12	47
Realized and unrealized gains on derivatives	3		1	4	2
Realized and unrealized gains on marketable securities	0		0	0	0
Other comprehensive income (loss)	6		32	16	49
Comprehensive income attributable to noncontrolling interests	49		65	103	110
Cash dividends - ordinary shares	0		0	0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(89)		(43)	(132)	(43)
Repurchase of ordinary shares	0		0	0	0
Change In noncontrolling interest share	0		19	0	19
Other, including options exercised	0		0	0	0
Ending balance	1,265	1,305	1,006	1,265	1,006
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21,407	22,458	21,500	22,458	21,367
Net income	558		471	957	729
Foreign currency translation adjustments	117		199	(1)	273
Realized and unrealized gains (losses) on derivatives	17		(5)	19	(3)
Realized and unrealized losses on marketable securities	0		(2)	0	(2)
Other comprehensive income	134		192	18	268
Total comprehensive income	692		663	975	997
Cash dividends - ordinary shares	(235)		(240)	(475)	(482)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(89)		(43)	(132)	(43)
Repurchase of ordinary shares	(533)		(49)	(1,000)	(199)
Change In noncontrolling interest share	0		19	0	19
Other, including options exercised	59		30	(66)	(42)
Ending balance	$ 21,301	21,407	$ 21,880	21,301	21,880
Accounting Standards Update 2016-09 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax					179
Accounting Standards Update 2016-09 [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				0	179
Accounting Standards Update 2016-09 [Member] | Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				0	0
Accounting Standards Update 2016-09 [Member] | Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				0	179
Accounting Standards Update 2016-16 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				(546)
Accounting Standards Update 2016-16 [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax		(546)		(546)	0
Accounting Standards Update 2016-16 [Member] | Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				0	0
Accounting Standards Update 2016-16 [Member] | Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				(546)	0
Accounting Standards Update 2014-09 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				(45)
Accounting Standards Update 2014-09 [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax		$ (45)		(45)	0
Accounting Standards Update 2014-09 [Member] | Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				0	0
Accounting Standards Update 2014-09 [Member] | Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax				$ (45)	$ 0