Stock-Based Compensation - Stock Appreciation Rights (Details) - Stock appreciation rights (SARs) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares
Weighted Average SAR Price
Shares outstanding, weighted average exercise price at beginning period (in dollars per share) | $ / shares	$ 32.78
Shares exercised, weighted average exercise price (in dollars per share) | $ / shares	30.14
Shares forfeited or expired, weighted average exercise price (in dollars per share) | $ / shares	39.52
Shares outstanding, weighted average exercise price at ending period (in dollars per share) | $ / shares	33.29
Shares exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 33.29
Shares Subject to SAR
Shares outstanding at beginning of period (In shares) | shares	103,884
Shares exercised (in shares) | shares	(53,844)
Shares forfeited or expired (In shares) | shares	(13,372)
Shares outstanding at ending of period (In shares) | shares	171,100
Shares exercisable (in shares) | shares	103,884
Weighted Average Remaining Contractual Life (years)
Shares outstanding, weighted average remaining contractual life	1 year 9 months 18 days
Shares exercisable, weighted average remaining contractual life	1 year 9 months 18 days
Aggregate Intrinsic Value (in millions)
Shares outstanding, aggregate intrinsic value | $	$ 3
Shares exercisable, aggregate intrinsic value | $	$ 3
Former Parent plan
Weighted Average SAR Price
Shares exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 33.00
Shares Subject to SAR
Shares exercisable (in shares) | shares	94,340
Weighted Average Remaining Contractual Life (years)
Shares exercisable, weighted average remaining contractual life	1 year 9 months 18 days
Aggregate Intrinsic Value (in millions)
Shares exercisable, aggregate intrinsic value | $	$ 3
Adient plan
Weighted Average SAR Price
Shares exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 36.17
Shares Subject to SAR
Shares exercisable (in shares) | shares	9,544
Weighted Average Remaining Contractual Life (years)
Shares exercisable, weighted average remaining contractual life	1 year 8 months 12 days
Aggregate Intrinsic Value (in millions)
Shares exercisable, aggregate intrinsic value | $	$ 0