Basis of Presentation and Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income (loss) attributable to Adient	$ 1,108	$ (547)	$ (491)
Denominator:
Shares outstanding (in shares)	94.2	93.8	93.6
Effect of dilutive securities (in shares)	1.5	0.0	0.0
Diluted shares (in shares)	95.7	93.8	93.6
Earnings per share:
Basic (in dollars per share)	$ 11.76	$ (5.83)	$ (5.25)
Diluted (in dollars per share)	$ 11.58	$ (5.83)	$ (5.25)