BUSINESS SEGMENT INFORMATION - Additional Information (Details) - segment	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of reportable segments	2
AB Volvo
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	22.00%	23.00%	22.00%
Daimler AG
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	19.00%	17.00%	17.00%
PACCAR
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	13.00%	12.00%	10.00%
Revenue from Contract with Customer Benchmark | Customer Concentration Risk | Navistar
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of sales to major customers	10.00%	9.00%	9.00%