EMPLOYEE BENEFIT PLANS - WEIGHTED AVERAGE ASSUMPTIONS (Details)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Pension
Benefit costs:
Expected asset return	7.00%	6.75%	6.75%
Pension | Represented
Benefit costs:
Discount rate	5.50%	3.10%	2.95%
Compensation increase	3.00%	3.00%	3.00%
Obligations:
Discount rate	5.89%	5.50%	3.10%
Compensation increase	3.00%	3.00%	3.00%
Pension | Nonrepresented
Benefit costs:
Discount rate	5.50%	3.07%	2.92%
Compensation increase	3.50%	3.50%	3.50%
Obligations:
Discount rate	5.87%	5.50%	3.07%
Compensation increase	3.50%	3.50%	3.50%
OPEB
Benefit costs:
Expected asset return	7.00%	6.75%	6.75%
OPEB | Represented
Benefit costs:
Discount rate	5.51%	3.24%	3.08%
Compensation increase	3.00%	3.00%	3.00%
Obligations:
Discount rate	5.97%	5.51%	3.24%
Compensation increase	3.00%	3.00%	3.00%
OPEB | Nonrepresented
Benefit costs:
Discount rate	5.51%	3.17%	3.03%
Compensation increase	3.50%	3.50%	3.50%
Obligations:
Discount rate	5.94%	5.51%	3.17%
Compensation increase	3.50%	3.50%	3.50%