Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Beginning balance	$ 4	$ 6
Charges to continuing operations	0	2
Cash payments – continuing operations	(1)	(3)
Ending balance	3	5
Less: non-current restructuring reserves	(1)	(2)	$ (1)
Restructuring reserves – current	2	3	$ 3
Employee Termination Benefits
Restructuring Reserve [Roll Forward]
Beginning balance	4	5
Charges to continuing operations	0	2
Cash payments – continuing operations	(1)	(2)
Ending balance	3	5
Less: non-current restructuring reserves	(1)	(2)
Restructuring reserves – current	2	3
Employee Termination Benefits | Commercial Truck & Trailer and Aftermarket and Industrial Segments
Restructuring Reserve [Roll Forward]
Charges to continuing operations		2
Plant Shutdown & Other
Restructuring Reserve [Roll Forward]
Beginning balance	0	1
Charges to continuing operations	0	0
Cash payments – continuing operations	0	(1)
Ending balance	0	0
Less: non-current restructuring reserves	0	0
Restructuring reserves – current	$ 0	$ 0