Debt and Financing Arrangements - Long-Term Debt (Details) € in Millions, ¥ in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2022 EUR (€)	Sep. 30, 2022 JPY (¥)
Debt Instrument [Line Items]
Other	$ 36	$ 25
Total	8,498	8,324
Less: current portion	645	865
Less: debt issuance costs	35	33
Long-term debt	$ 7,818	7,426
4.625% Due in 2023 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.625%
Debt instrument, face amount		25
Long-term debt	$ 0	25
4.625% Due in 2023 | Tyco International Finance S.A. (TIFSA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.625%
Debt instrument, face amount		7
Long-term debt	$ 0	7
1.00% Due in 2023 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.00%
Debt instrument, face amount | €			€ 846
Long-term debt	$ 0	830
3.625% Due in 2024 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.625%
Debt instrument, face amount		453
Long-term debt	$ 453	453
3.625% Due in 2024 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.625%
Debt instrument, face amount		31
Long-term debt	$ 31	31
EURIBOR Plus 0.70% | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, face amount | €			150
Long-term debt	$ 159	0
EURIBOR Plus 0.70% | Johnson Controls International plc | Tokyo Term Risk Free Rate (TORF)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.70%
1.375% Due in 2025 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.375%
Debt instrument, face amount | €			423
Long-term debt	$ 450	419
1.375% Due in 2025 | Tyco International Finance S.A. (TIFSA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.375%
Debt instrument, face amount | €			54
Long-term debt	$ 57	53
3.90% Due in 2026 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.90%
Debt instrument, face amount		487
Long-term debt	$ 499	505
3.90% Due in 2026 | Tyco International Finance S.A. (TIFSA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.90%
Debt instrument, face amount		51
Long-term debt	$ 50	51
TORF JPY Plus 0.40% Due in 2027 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, face amount | ¥				¥ 30,000
Long-term debt	$ 202	208
TORF JPY Plus 0.40% Due in 2027 | Johnson Controls International plc | Tokyo Term Risk Free Rate (TORF)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.40%
0.375% Due in 2027 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.375%
Debt instrument, face amount | €			500
Long-term debt	$ 528	488
3.00 % Due in 2028 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.00%
Debt instrument, face amount | €			600
Long-term debt	$ 634	586
1.75% Due in 2030 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.75%
Debt instrument, face amount		625
Long-term debt	$ 624	623
2.00% Due in 2031 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%
Debt instrument, face amount		500
Long-term debt	$ 497	496
1.00% Due in 2032 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.00%
Debt instrument, face amount | €			500
Long-term debt	$ 529	489
4.90% Due in 2032 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.90%
Debt instrument, face amount		400
Long-term debt	$ 394	394
4.25% Due in 2035 | Johnson Controls International plc (JCI) and Tyco Fire & Security Finance S.C.A. (TFSCA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.25%
Debt instrument, face amount | €			€ 800
Long-term debt	$ 839	0
6.00% Due in 2036 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.00%
Debt instrument, face amount		342
Long-term debt	$ 339	339
6.00% Due in 2036 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.00%
Debt instrument, face amount		8
Long-term debt	$ 8	8
5.70% Due in 2041 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.70%
Debt instrument, face amount		190
Long-term debt	$ 189	189
5.70% Due in 2041 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.70%
Debt instrument, face amount		30
Long-term debt	$ 30	30
5.25% Due in 2042 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
Debt instrument, face amount		155
Long-term debt	$ 155	155
5.25% Due in 2042 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
Debt instrument, face amount		6
Long-term debt	$ 6	6
4.625% Due in 2044 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.625%
Debt instrument, face amount		444
Long-term debt	$ 442	441
4.625% Due in 2044 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.625%
Debt instrument, face amount		6
Long-term debt	$ 6	6
5.125% Due in 2045 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.125%
Debt instrument, face amount		477
Long-term debt	$ 431	557
5.125% Due in 2045 | Tyco International Finance S.A. (TIFSA)
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.125%
Debt instrument, face amount		23
Long-term debt	$ 23	23
6.95% Due in 2046 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.95%
Debt instrument, face amount		32
Long-term debt	$ 32	32
6.95% Due in 2046 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.95%
Debt instrument, face amount		4
Long-term debt	$ 4	4
4.50% Due in 2047 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.50%
Debt instrument, face amount		500
Long-term debt	$ 496	496
4.95% Due in 2064 | Johnson Controls International plc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.95%
Debt instrument, face amount		341
Long-term debt	$ 340	340
4.95% Due in 2064 | Johnson Controls Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.95%
Debt instrument, face amount		15
Long-term debt	$ 15	$ 15