Fair Value Measurements - Schedule of the Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2025	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Other current assets
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other noncurrent assets	Other noncurrent assets
Total assets	$ 33	$ 18
Total liabilities	13	41
Foreign currency exchange derivatives \| Other current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	30	15
Foreign currency exchange derivatives \| Other noncurrent assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3	3
Foreign currency exchange derivatives \| Other current liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	10	32
Foreign currency exchange derivatives \| Other noncurrent liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	3	9
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Total liabilities	0	0
Quoted Prices in Active Markets (Level 1) \| Foreign currency exchange derivatives \| Other current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Quoted Prices in Active Markets (Level 1) \| Foreign currency exchange derivatives \| Other noncurrent assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Quoted Prices in Active Markets (Level 1) \| Foreign currency exchange derivatives \| Other current liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Quoted Prices in Active Markets (Level 1) \| Foreign currency exchange derivatives \| Other noncurrent liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	33	18
Total liabilities	13	41
Significant Other Observable Inputs (Level 2) \| Foreign currency exchange derivatives \| Other current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	30	15
Significant Other Observable Inputs (Level 2) \| Foreign currency exchange derivatives \| Other noncurrent assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3	3
Significant Other Observable Inputs (Level 2) \| Foreign currency exchange derivatives \| Other current liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	10	32
Significant Other Observable Inputs (Level 2) \| Foreign currency exchange derivatives \| Other noncurrent liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	3	9
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Total liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Foreign currency exchange derivatives \| Other current assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Significant Unobservable Inputs (Level 3) \| Foreign currency exchange derivatives \| Other noncurrent assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Significant Unobservable Inputs (Level 3) \| Foreign currency exchange derivatives \| Other current liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Significant Unobservable Inputs (Level 3) \| Foreign currency exchange derivatives \| Other noncurrent liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 0	$ 0

Adient plc 10-Q