Debt and Financing Arrangements Financing Arrangements (Details) ¥ in Billions				3 Months Ended					12 Months Ended
	Oct. 04, 2017 USD ($)	Dec. 28, 2016 USD ($)	Dec. 28, 2016 EUR (€)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 JPY (¥)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 JPY (¥)	Mar. 31, 2017 EUR (€)	Dec. 28, 2016 EUR (€)	Sep. 30, 2016 EUR (€)	Mar. 31, 2016 USD ($)
Debt Instrument [Line Items]
Debt traunches									4
Amount Of Credit Facility Retired | €											€ 390,000,000
Number of term loans repaid									3
LIBOR plus One Point Zero Zero Five Percent Due Two Thousand Twenty One [Member]
Debt Instrument [Line Items]
Interest rate on notes								1.005%		1.005%					1.005%
Three Point Five Percent Due Two Thousand Twenty Four [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | €											€ 1,000,000,000
Interest rate on notes				3.50%					3.50%		3.50%	3.50%
Committed Five-year Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Term					5 years
Amount Of Credit Facility Retired								$ 2,500,000,000		$ 2,500,000,000
Dollar denominated notes [Member]
Debt Instrument [Line Items]
Debt Conversion, Converted Instrument, Amount		$ 5,600,000,000
Debt Conversion, Original Debt, Amount		6,000,000,000
Aggregrate principal amount of existing notes outstanding		$ 380,900,000
Series of existing notes outstanding		17
Euro denominated notes [Member]
Debt Instrument [Line Items]
Debt Conversion, Converted Instrument, Amount | €			€ 423,000,000
Debt Conversion, Original Debt, Amount | €			€ 500,000,000
Aggregrate principal amount of existing notes outstanding | €														€ 77,400,000
Series of existing notes outstanding		1
Four Point Eight Seven Five Percent Due Two Thousand Twenty Six [Member]
Debt Instrument [Line Items]
Debt Instrument, Term								10 years
Three Point Five Percent Due Two Thousand Twenty Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Term								8 years
500 million USD floating rate term loan maturing in September 2016 [Member]
Debt Instrument [Line Items]
Debt retired, amount								$ 500,000,000
100 Million USD floating rate term loan maturing in Nov 2016 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Term						9 months	9 months
Debt retired, amount						$ 100,000,000
125 Million USD floating rate term loan maturing in Sept 2016 [Member]
Debt Instrument [Line Items]
Debt retired, amount								125,000,000
200 Million USD floating rate term loan maturing in Sept 2016 [Domain]
Debt Instrument [Line Items]
Debt retired, amount								200,000,000
90 million USD revolving credit facility
Debt Instrument [Line Items]
Debt retired, amount										90,000,000
35 billion yen floating rate syndicated term loan maturing in September 2022 [Domain]
Debt Instrument [Line Items]
Debt instrument, face amount | ¥												¥ 35
Debt Instrument, Term				5 years
Seven Point One Two Five Percent Due Two Thousand Seventeen [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms				0.07125
Debt retired, amount				$ 150,000,000
One percent maturing in fiscal 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | €													€ 1,000,000,000
Debt Instrument, Interest Rate Terms					0.01
Two Point Three Five Five Percent Due Two Thousand Seventeen
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms					0.02355
Debt retired, amount					$ 46,000,000
One Point Three Seven Five Percent Due in Two Thousand Twenty Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms				0.01375	0.01375
Debt Instrument, Repurchase Amount | €											€ 4,000,000		€ 15,000,000
Four point five percent maturing in fiscal 2047 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 500,000,000
Debt Instrument, Interest Rate Terms					0.045
Two Point Six Percent Due Two Thousand Seventeen
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms						0.026	0.026
Debt retired, amount						$ 400,000,000
37 billion yen floating rate syndicated term loan maturing in June 2020 [Member]
Debt Instrument [Line Items]
Debt retired, amount | ¥							¥ 37
Contingent on consumation of Tyco merger [Domain] | 2.0 billion USD revolving credit facility [Domain]
Debt Instrument [Line Items]
Debt Instrument, Term									4 years
Line of Credit Facility, Maximum Borrowing Capacity																$ 2,000,000,000
Proceeds from Lines of Credit									$ 0	0
Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Long-term Debt								4,000,000,000		4,000,000,000
Repayments of Debt									300,000,000
Tyco International Holding S.a.r.L. (TSarL) [Member] | LIBOR plus One Point Five Percent Due in Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 3,700,000,000				4,000,000,000	3,700,000,000	4,000,000,000
Johnson Controls International plc [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Unsecured Debt									1,500,000,000
Johnson Controls International plc [Member] | 1.4% Due in 2018
Debt Instrument [Line Items]
Long-term Debt				259,000,000				0	259,000,000	0
Debt instrument, face amount				$ 259,000,000					$ 259,000,000
Interest rate on notes				1.40%					1.40%		1.40%	1.40%
Johnson Controls International plc [Member] | Three Point Six Two Five Percent Due Two Thousand Twenty Four [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 468,000,000				0	$ 468,000,000	0
Debt instrument, face amount				$ 468,000,000					$ 468,000,000
Interest rate on notes				3.625%					3.625%		3.625%	3.625%
Johnson Controls International plc [Member] | Four Point Nine Five Percent Due Two Thousand Sixty Four [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 434,000,000				$ 0	$ 434,000,000	0
Debt instrument, face amount				$ 435,000,000					$ 435,000,000
Interest rate on notes				4.95%					4.95%		4.95%	4.95%
Adient
Debt Instrument [Line Items]
Debt Instrument, Term								5 years
Line of Credit Facility, Maximum Borrowing Capacity								$ 1,500,000,000		1,500,000,000
Proceeds from Issuance of Unsecured Debt									$ 500,000,000
Proceeds from Lines of Credit									0
Adient | LIBOR plus One Point Zero Zero Five Percent Due Two Thousand Twenty One [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 0				$ 1,500,000,000	0	1,500,000,000
Debt Instrument, Term								5 years
Adient | Three Point Five Percent Due Two Thousand Twenty Four [Member]
Debt Instrument [Line Items]
Long-term Debt				$ 0				$ 1,119,000,000	$ 0	$ 1,119,000,000
Debt instrument, face amount | €															€ 1,000,000,000
Interest rate on notes								3.50%		3.50%					3.50%
Subsequent Event [Member] | Tyco International Holding S.a.r.L. (TSarL) [Member]
Debt Instrument [Line Items]
Repayments of Debt	$ 1,900,000,000