Retirement and Post-Retirement Employee Benefit Plans - Schedule of Assumptions Used (Details)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate Pension Liability	2.80%	3.29%
Discount rate Pension Cost	3.29%	4.38%	3.89%
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%	6.50%
Expected return on plan assets Pension Cost	6.50%	6.75%	6.75%
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	2.80%	3.29%
Discount rate Pension Cost	3.19%	4.38%	4.08%
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%