Retirement and Postretirement Employee Benefit Plans - Schedule of Assumptions Used (Details)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Employee Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate pension liability	6.10%	5.66%
Discount rate pension cost	5.66%	2.97%	2.80%
Rate of compensation increase pension liability	3.50%	3.50%
Rate of compensation increase pension cost	3.50%	3.50%	3.50%
Expected return on plan assets pension liability	6.25%	6.25%
Expected return on plan assets pension cost	6.25%	6.25%	6.25%
Interest crediting rate increase pension liability	4.69%	4.69%
Interest crediting rate increase pension cost	4.69%	4.69%	4.69%
Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate pension liability	6.17%	5.71%
Discount rate pension cost	5.50%	2.57%	2.90%
Rate of compensation increase pension liability	3.50%	3.50%
Rate of compensation increase pension cost	3.50%	3.50%	3.50%
Interest crediting rate increase pension liability	4.69%	4.69%
Interest crediting rate increase pension cost	4.69%	4.69%	4.69%