Segment Information - Reportable Segment Adjusted EBITDA is Reconciled to Income (Loss) Before Income Taxes (Details)	1 Months Ended	3 Months Ended			12 Months Ended
	Nov. 30, 2023 USD ($)	Sep. 30, 2025 USD ($)	Mar. 31, 2025 segment	Dec. 31, 2024 USD ($)	Sep. 30, 2025 USD ($) segment	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			3		3
Segment Reporting Information [Line Items]
Net sales					$ 14,535,000,000	$ 14,688,000,000	$ 15,395,000,000
Administrative, engineering and allocated costs					522,000,000	507,000,000	554,000,000
Equity income					68,000,000	90,000,000	84,000,000
Adjusted EBITDA					966,000,000	969,000,000	1,032,000,000
Corporate - related costs					(85,000,000)	(89,000,000)	(94,000,000)
Restructuring and impairment costs					(392,000,000)	(168,000,000)	(40,000,000)
Purchase accounting amortization					(47,000,000)	(48,000,000)	(52,000,000)
Restructuring-related activities					(11,000,000)	0	2,000,000
Gain (loss) on disposal transactions					4,000,000	(7,000,000)	(6,000,000)
Depreciation expense					(279,000,000)	(285,000,000)	(290,000,000)
Equity based compensation					(32,000,000)	(31,000,000)	(34,000,000)
Other items					(9,000,000)	2,000,000	5,000,000
Net financing charges					(193,000,000)	(189,000,000)	(195,000,000)
Other pension expense					(10,000,000)	(21,000,000)	(33,000,000)
Income (loss) before income taxes					(88,000,000)	133,000,000	295,000,000
Impairment		$ 0			333,000,000
Restructuring charges					58,000,000	169,000,000	39,000,000
(Gain) on sale of / impairment of nonconsolidated partially-owned affiliates						1,000,000
Consulting fees					10,000,000
One-time gain					2,000,000	3,000,000
Transaction costs						1,000,000
Gain on business divestitures					4,000,000	1,000,000
Integration-related costs							3,000,000
BRAZIL
Segment Reporting Information [Line Items]
Tax adjustments						1,000,000	4,000,000
TURKEY
Segment Reporting Information [Line Items]
One-time divestiture related tax impact						1,000,000
Gain on business divestitures							4,000,000
Disposed of By Sale | Adient (Langfang) Seating Co., Ltd
Segment Reporting Information [Line Items]
Loss on disposal	$ 8,000,000
Subsidiary, ownership percentage disposed (as percent)	51.00%
Restructured Facility
Segment Reporting Information [Line Items]
Restructuring charges					29,000,000	10,000,000	6,000,000
Gain on disposition of property plant equipment					23,000,000	10,000,000	10,000,000
Adient Aerospace
Segment Reporting Information [Line Items]
(Gain) on sale of / impairment of nonconsolidated partially-owned affiliates					8,000,000	9,000,000
Nonconsolidated Investees, Other
Segment Reporting Information [Line Items]
Restructuring charges					5,000,000
Nonconsolidated Investees, Other | Restructured Facility
Segment Reporting Information [Line Items]
Restructuring charges					5,000,000		2,000,000
Setex, Inc.
Segment Reporting Information [Line Items]
Realized gain on disposal				$ 4,000,000	4,000,000
Affilliates
Segment Reporting Information [Line Items]
Equity income					(1,000,000)
Americas
Segment Reporting Information [Line Items]
Impairment					0
EMEA
Segment Reporting Information [Line Items]
Impairment					333,000,000
Restructuring charges					51,000,000	159,000,000	40,000,000
(Gain) on sale of / impairment of nonconsolidated partially-owned affiliates							3,000,000
Asia
Segment Reporting Information [Line Items]
Impairment					0
(Gain) on sale of / impairment of nonconsolidated partially-owned affiliates							3,000,000
Reportable Segments
Segment Reporting Information [Line Items]
Net sales					14,612,000,000	14,781,000,000	15,500,000,000
Reportable Segments | Americas
Segment Reporting Information [Line Items]
Net sales					6,856,000,000	6,763,000,000	7,220,000,000
Material costs					4,444,000,000	4,394,000,000	4,755,000,000
Labor and overhead					1,819,000,000	1,841,000,000	1,926,000,000
Administrative, engineering and allocated costs					191,000,000	156,000,000	206,000,000
Equity income					0	3,000,000	3,000,000
Adjusted EBITDA					402,000,000	375,000,000	336,000,000
Reportable Segments | EMEA
Segment Reporting Information [Line Items]
Net sales					4,773,000,000	5,029,000,000	5,195,000,000
Material costs					2,958,000,000	3,123,000,000	3,268,000,000
Labor and overhead					1,495,000,000	1,568,000,000	1,517,000,000
Administrative, engineering and allocated costs					213,000,000	198,000,000	193,000,000
Equity income					17,000,000	15,000,000	15,000,000
Adjusted EBITDA					124,000,000	155,000,000	232,000,000
Reportable Segments | Asia
Segment Reporting Information [Line Items]
Net sales					2,983,000,000	2,989,000,000	3,085,000,000
Material costs					2,056,000,000	2,061,000,000	2,096,000,000
Labor and overhead					419,000,000	426,000,000	463,000,000
Administrative, engineering and allocated costs					122,000,000	136,000,000	134,000,000
Equity income					54,000,000	73,000,000	72,000,000
Adjusted EBITDA					440,000,000	439,000,000	464,000,000
Inter-segment elimination
Segment Reporting Information [Line Items]
Net sales					$ (77,000,000)	$ (93,000,000)	$ (105,000,000)