Restructuring and Impairment Costs (Details) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($) employee plant	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Underspend			$ 7
Restructuring and impairment costs	$ 31	$ 0
Number of positions eliminated to date | employee	6,800
Number of positions eliminated | employee	4,300
Number of plants expected to close | plant	14
Number of plants closed | plant	9
2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross	$ 25
2019 Restructuring Plan | SS&M
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross	12
2019 Restructuring Plan | Seating
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross	$ 13
2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			71
2018 Restructuring Plan | SS&M
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			23
2018 Restructuring Plan | Seating
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs, gross			48
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				$ 46
2016 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Underspend			20
Restructuring and impairment costs					$ 332
2016 Restructuring Plan | Employee Severance and Termination Benefits
Restructuring Cost and Reserve [Line Items]
Underspend			$ 20
2016 Restructuring Plan | SS&M
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					98
2016 Restructuring Plan | Seating
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					217
2016 Restructuring Plan | Interiors
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 17