Debt and Financing Arrangements Long-Term Debt (Details)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Sep. 30, 2018 JPY (¥)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Other Long-term Debt	$ 23,000,000			$ 90,000,000
Capital lease obligations	36,000,000			19,000,000
Long-term Debt and Capital Lease Obligations, Including Current Maturities	9,724,000,000			12,403,000,000
Less: current portion	26,000,000			394,000,000
Debt Issuance Costs, Line of Credit Arrangements, Gross	44,000,000			45,000,000
Net long-term debt	$ 9,654,000,000			11,964,000,000
Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Long-term Debt					$ 4,000,000,000
1.4% Due in 2018
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.40%	1.40%	1.40%
1.4% Due in 2018 | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.40%	1.40%	1.40%
Debt instrument, face amount	$ 41,000,000
Long-term Debt	$ 0			42,000,000
1.4% Due in 2018 | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.40%	1.40%	1.40%
Debt instrument, face amount	$ 259,000,000
Long-term Debt	$ 0			259,000,000
Three Point Seven Five Percent Due in Two Thousand Eighteen [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%	3.75%
Debt instrument, face amount	$ 49,000,000
Long-term Debt	$ 0			49,000,000
Three Point Seven Five Percent Due in Two Thousand Eighteen [Member] | Tyco International Finance S.A. (TIFSA) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%	3.75%
Debt instrument, face amount	$ 18,000,000
Long-term Debt	$ 0			18,000,000
5.0 % Due in 2020 | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%	5.00%	5.00%
Debt instrument, face amount	$ 47,000,000
Long-term Debt	$ 47,000,000			47,000,000
5.0 % Due in 2020 | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%	5.00%	5.00%
Debt instrument, face amount	$ 453,000,000
Long-term Debt	$ 452,000,000			452,000,000
Zero Point Zero Percent Due Two Thousand Twenty-One [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.00%	0.00%	0.00%
Debt instrument, face amount | €		€ 750,000,000
Long-term Debt	$ 868,000,000			0
4.25% Due in 2021 | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.25%	4.25%	4.25%
Debt instrument, face amount	$ 53,000,000
Long-term Debt	$ 53,000,000			53,000,000
4.25% Due in 2021 | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.25%	4.25%	4.25%
Debt instrument, face amount	$ 447,000,000
Long-term Debt	$ 446,000,000			446,000,000
3.75 % Due in 2022 | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%	3.75%
Debt instrument, face amount	$ 22,000,000
Long-term Debt	$ 22,000,000			22,000,000
3.75 % Due in 2022 | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%	3.75%	3.75%
Debt instrument, face amount	$ 428,000,000
Long-term Debt	$ 427,000,000			427,000,000
Four Point Six Two Five Percent Due in Two Thousand Twenty Three [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.625%	4.625%	4.625%
Debt instrument, face amount	$ 35,000,000
Long-term Debt	$ 37,000,000			38,000,000
Four Point Six Two Five Percent Due in Two Thousand Twenty Three [Member] | Tyco International Finance S.A. (TIFSA) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.625%	4.625%	4.625%
Debt instrument, face amount	$ 7,000,000
Long-term Debt	$ 8,000,000			8,000,000
One Point Zero Percent Due Two Thousand Twenty Three | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.00%	1.00%	1.00%
Debt instrument, face amount | €		€ 1,000,000,000
Long-term Debt	$ 1,154,000,000			1,171,000,000
Three Point Six Two Five Percent Due Two Thousand Twenty Four [Member] | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.625%	3.625%	3.625%
Debt instrument, face amount	$ 31,000,000
Long-term Debt	$ 31,000,000			31,000,000
Three Point Six Two Five Percent Due Two Thousand Twenty Four [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.625%	3.625%	3.625%
Debt instrument, face amount	$ 468,000,000
Long-term Debt	$ 468,000,000			468,000,000
One Point Three Seven Five Percent Due in Two Thousand Twenty Five [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.375%	1.375%	1.375%
Debt instrument, face amount | €		€ 423,000,000
Long-term Debt	$ 501,000,000			510,000,000
One Point Three Seven Five Percent Due in Two Thousand Twenty Five [Member] | Tyco International Finance S.A. (TIFSA) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.375%	1.375%	1.375%
Debt instrument, face amount | €		€ 58,000,000
Long-term Debt	$ 69,000,000			70,000,000
One Point Three Seven Five Percent Due in Two Thousand Twenty Five [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | €		€ 215,000,000
Three Point Ninety Percent Due in Two Thousand Twenty Six [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.90%	3.90%	3.90%
Debt instrument, face amount	$ 698,000,000
Long-term Debt	$ 755,000,000			763,000,000
Three Point Ninety Percent Due in Two Thousand Twenty Six [Member] | Tyco International Finance S.A. (TIFSA) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.90%	3.90%	3.90%
Debt instrument, face amount	$ 51,000,000
Long-term Debt	$ 52,000,000			53,000,000
Six Point Zero Percent Due Two Thousand Thirty Six [Member] | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%	6.00%
Debt instrument, face amount	$ 8,000,000
Long-term Debt	$ 8,000,000			8,000,000
Six Point Zero Percent Due Two Thousand Thirty Six [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%	6.00%
Debt instrument, face amount	$ 392,000,000
Long-term Debt	$ 388,000,000			388,000,000
Five Point Seven Percent Due Two Thousand Forty One | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.70%	5.70%	5.70%
Debt instrument, face amount	$ 30,000,000
Long-term Debt	$ 30,000,000			30,000,000
Five Point Seven Percent Due Two Thousand Forty One | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.70%	5.70%	5.70%
Debt instrument, face amount	$ 270,000,000
Long-term Debt	$ 269,000,000			269,000,000
Five Point Two Five Percent Due Two Thousand Forty Two | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.25%	5.25%	5.25%
Debt instrument, face amount	$ 8,000,000
Long-term Debt	$ 8,000,000			8,000,000
Five Point Two Five Percent Due Two Thousand Forty Two | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.25%	5.25%	5.25%
Debt instrument, face amount	$ 242,000,000
Long-term Debt	$ 242,000,000			242,000,000
Four Point Six Two Five Percent Due Two Thousand Forty Four | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.625%	4.625%	4.625%
Debt instrument, face amount	$ 6,000,000
Long-term Debt	$ 6,000,000			6,000,000
Four Point Six Two Five Percent Due Two Thousand Forty Four | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.625%	4.625%	4.625%
Debt instrument, face amount	$ 445,000,000
Long-term Debt	$ 441,000,000			441,000,000
Five Point One Two Five Percent Due in Two Thousand Forty Five [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.125%	5.125%	5.125%
Debt instrument, face amount	$ 727,000,000
Long-term Debt	$ 867,000,000			872,000,000
Five Point One Two Five Percent Due in Two Thousand Forty Five [Member] | Tyco International Finance S.A. (TIFSA) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.125%	5.125%	5.125%
Debt instrument, face amount	$ 23,000,000
Long-term Debt	$ 23,000,000			23,000,000
Six Point Nine Five Percent Due Two Thousand Forty Six | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.95%	6.95%	6.95%
Debt instrument, face amount	$ 4,000,000
Long-term Debt	$ 4,000,000			4,000,000
Six Point Nine Five Percent Due Two Thousand Forty Six | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.95%	6.95%	6.95%
Debt instrument, face amount	$ 121,000,000
Long-term Debt	$ 121,000,000			121,000,000
Four point five percent maturing in fiscal 2047 [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.50%	4.50%	4.50%
Debt instrument, face amount	$ 500,000,000
Long-term Debt	$ 496,000,000			495,000,000
Four Point Nine Five Percent Due Two Thousand Sixty Four [Member] | Johnson Controls Inc. [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.95%	4.95%	4.95%
Debt instrument, face amount	$ 15,000,000
Long-term Debt	$ 15,000,000			15,000,000
Four Point Nine Five Percent Due Two Thousand Sixty Four [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.95%	4.95%	4.95%
Debt instrument, face amount	$ 435,000,000
Long-term Debt	$ 434,000,000			434,000,000
LIBOR plus One Point Two Five Percent Due in Two Thousand Twenty [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.25%	1.25%	1.25%
Long-term Debt	$ 364,000,000
EURIBOR plus Zero Point Six Two Percent due in Two Thousand Twenty [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.62%	0.62%	0.62%
Long-term Debt	$ 250,000,000
LIBOR JPY Plus Zero Point Four Two Percent Due in Two Thousand Twenty Two [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	0.40%	0.40%	0.40%
Debt instrument, face amount | ¥			¥ 35,000,000,000
Long-term Debt	$ 309,000,000
LIBOR JPY Plus Zero Point Four Two Percent Due in Two Thousand Twenty Two [Member] | Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Long-term Debt				311,000,000
EURIBOR plus Zero Point Six Two Percent due in Two Thousand Twenty [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Long-term Debt				0
LIBOR plus One Point Two Five Percent Due in Two Thousand Twenty [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 3,700,000,000	$ 4,000,000,000