Retirement and Postretirement Employee Benefit Plans - Actuarial Assumptions For Net Periodic Pension Cost (Details) - Postretirement Plan	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Discount rate pension asset	5.47%	5.01%
Discount rate postretirement cost	5.01%	6.06%	5.61%
Expected return on plan assets pension asset	5.14%	5.14%
Expected return on plan assets postretirement cost	5.14%	4.94%	4.94%
Initial trend rate pension asset	7.00%	6.75%
Initial trend rate postretirement cost	6.75%	6.50%	6.25%
Ultimate trend rate pension asset	5.00%	5.00%
Ultimate trend rate postretirement cost	5.00%	5.00%	4.75%