EMPLOYEE BENEFIT PLANS - ADDITIONAL INFORMATION (Details) - USD ($)	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 0	$ 0
OPEB | Minimum
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions	5,000,000
OPEB | Maximum
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions	$ 10,000,000