Basis of Presentation and Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Millions		2 Months Ended	12 Months Ended
	Oct. 01, 2019 USD ($)	Apr. 30, 2020	Sep. 30, 2021 USD ($) entity $ / shares shares	Sep. 30, 2020 USD ($) entity	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Oct. 31, 2016 $ / shares shares
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common stock, shares authorized (in shares) | shares			500,000,000				500,000,000
Preferred stock, shares authorized (in shares) | shares			100,000,000				100,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.001				$ 0.001
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.001				$ 0.001
Common stock, shares issued (in shares) | shares			94,378,004				93,671,810
Number of VIE entities | entity			2	2
Engineering, research and development, and other design and development costs			$ 278	$ 293
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-02 [Member]
Operating lease right-of-use assets			335	334
Present value of lease liabilities			335	339
Increase in opening accumulated deficit			(2,718)	(1,535)	$ (2,189)	$ (2,717)
Research and development costs			316	370	454
Research and development costs reimbursed by customers			210	223	291
Foreign currency translation gain (loss)			$ (8)	(25)	(12)
Cumulative effect, period of adoption, adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating lease right-of-use assets	$ 380			380
Present value of lease liabilities	384			$ 384
Increase in opening accumulated deficit	$ 4				$ 4
Other Asia
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Percentage of plants shutdown		50.00%
Stellantis N.V. | Customer concentration risk | Net sales
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Concentration risk (as percent)			13.00%	10.00%	11.00%
Volkswagen Group | Customer concentration risk | Net sales
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Concentration risk (as percent)			11.00%	10.00%	9.00%
Minimum | Buildings and improvements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Useful life			3 years
Minimum | Machinery and equipment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Useful life			3 years
Maximum | Buildings and improvements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Useful life			40 years
Maximum | Machinery and equipment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Useful life			15 years
Current assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Engineering, research and development, and other design and development costs			$ 66	$ 85
Costs for molds, dies and other tools to be reimbursed by customer			77	78
Noncurrent assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Engineering, research and development, and other design and development costs			212	208
Costs for molds, dies and other tools to be reimbursed by customer			8	6
Property, plant and equipment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Costs for molds, dies and other tools with title			$ 62	$ 51