Restructuring Costs - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019	Sep. 27, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring reserves	$ 7	$ 7	$ 2	$ 8		$ 4
Restructuring costs		15	$ (1)
Global Restructuring Programs | Commercial Truck
Restructuring Cost and Reserve [Line Items]
Restructuring costs	8
Restructuring costs incurred to date	19	$ 19
Global Restructuring Programs | Employee severance
Restructuring Cost and Reserve [Line Items]
Restructuring costs expected to be incurred					$ 20
Increase in restructuring costs expected to be incurred	$ 6