Equity and Noncontrolling Interests - Equity Attributable to Johnson Controls and Noncontrolling Interests (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 21,164	$ 20,447
Beginning balance	1,294
Beginning balance	22,458
Foreign currency translation adjustments	(118)	79
Realized and unrealized gains (losses) on derivatives	2	(1)
Other comprehensive income (loss)	(116)	78
Comprehensive income attributable to Johnson Controls	229	289
Comprehensive income attributable to noncontrolling interests	54	60
Total comprehensive income	283	349
Cash dividends - ordinary shares	(240)	(242)
Repurchase of ordinary shares	(467)	(150)
Other, including options exercised	7	12
Ending balance	20,102	20,535
Ending balance	1,305
Ending balance	21,407
Net income (loss) attributable to Johnson Controls	355	230
Equity Attributable to Johnson Controls
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21,164	20,447
Foreign currency translation adjustments	(127)	58
Realized and unrealized gains (losses) on derivatives	1	1
Other comprehensive income (loss)	(126)	59
Comprehensive income attributable to Johnson Controls	229	289
Cash dividends - ordinary shares	(240)	(242)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	0	0
Repurchase of ordinary shares	(467)	(150)
Other, including options exercised	7	12
Ending balance	20,102	20,535
Net income (loss) attributable to Johnson Controls	355	230
Equity Attributable to Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,294	920
Income attributable to noncontrolling interests	44	28
Foreign currency translation adjustments	9	16
Realized and unrealized gains on derivatives	1	1
Other comprehensive income (loss)	10	17
Comprehensive income attributable to noncontrolling interests	54	45
Cash dividends - ordinary shares	0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(43)	0
Repurchase of ordinary shares	0	0
Other, including options exercised	0	0
Ending balance	1,305	965
Total Equity Excluding Redeemable Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	22,458	21,367
Net income	399	258
Foreign currency translation adjustments	(118)	74
Realized and unrealized gains (losses) on derivatives	2	2
Other comprehensive income (loss)	(116)	76
Total comprehensive income	283	334
Cash dividends - ordinary shares	(240)	(242)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(43)	0
Repurchase of ordinary shares	(467)	(150)
Other, including options exercised	7	12
Ending balance	21,407	21,500
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)	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)	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