Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 20,447
Beginning balance	920
Beginning balance	21,367
Foreign currency translation adjustments	79	$ (703)
Realized and unrealized gains (losses) on derivatives	(1)	4
Realized and unrealized losses on marketable securities	0	(2)
Other comprehensive income (loss)	78	(701)
Comprehensive income (loss) attributable to Johnson Controls	289	(332)
Comprehensive income attributable to noncontrolling interests	60	9
Total comprehensive income (loss)	349	(323)
Repurchase of ordinary shares	(150)	0
Ending balance	20,535
Ending balance	965
Ending balance	21,500
Net income attributable to Johnson Controls	230	329
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	20,447	24,118
Foreign currency translation adjustments	58	(659)
Realized and unrealized gains (losses) on derivatives	1	0
Realized and unrealized losses on marketable securities	0	(2)
Other comprehensive income (loss)	59	(661)
Comprehensive income (loss) attributable to Johnson Controls	289	(332)
Cash dividends - ordinary shares	(242)	(236)
Repurchase of ordinary shares	(150)	0
Change In noncontrolling interest share	0	0
Spin-off of Adient	0	(4,020)
Other, including options exercised	12	47
Ending balance	20,535	19,577
Net income attributable to Johnson Controls	230	329
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	920	972
Income attributable to noncontrolling interests	28	36
Foreign currency translation adjustments	16	(35)
Realized and unrealized gains on derivatives	1	4
Realized and unrealized gains on marketable securities	0	0
Other comprehensive income (loss)	17	(31)
Comprehensive income attributable to noncontrolling interests	45	5
Cash dividends - ordinary shares	0	0
Repurchase of ordinary shares	0	0
Change In noncontrolling interest share	0	(20)
Spin-off of Adient	0	(138)
Other, including options exercised	0	0
Ending balance	965	819
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21,367	25,090
Net income	258	365
Foreign currency translation adjustments	74	(694)
Realized and unrealized gains (losses) on derivatives	2	4
Realized and unrealized losses on marketable securities	0	(2)
Other comprehensive income (loss)	76	(692)
Total comprehensive income (loss)	334	(327)
Cash dividends - ordinary shares	(242)	(236)
Repurchase of ordinary shares	(150)	0
Change In noncontrolling interest share	0	(20)
Spin-off of Adient	0	(4,158)
Other, including options exercised	12	47
Ending balance	21,500	20,396
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		(659)
Realized and unrealized gains (losses) on derivatives	1	0
Realized and unrealized losses on marketable securities	0	(2)
Other comprehensive income (loss)	59	(661)
Comprehensive income (loss) attributable to Johnson Controls	289	(332)
Comprehensive income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	289	(332)
Ending balance	20,535
Ending balance	0
Ending balance	20,535
Net income attributable to Johnson Controls	230	329
Parent Company [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustments	58
Adjustments for New Accounting Pronouncement [Member] | Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	179	0
Adjustments for New Accounting Pronouncement [Member] | Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	0	0
Adjustments for New Accounting Pronouncement [Member] | Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 179	$ 0