Retirement and Postretirement Employee Benefit Plans - Asset Allocation (Details)	Sep. 30, 2023	Sep. 30, 2022
Employee Pension Plan | Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	42.90%	39.70%
Employee Pension Plan | Domestic equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	35.00%
Employee Pension Plan | Domestic equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	55.00%
Employee Pension Plan | International equities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	16.00%	14.60%
Employee Pension Plan | International equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	10.00%
Employee Pension Plan | International equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	20.00%
Employee Pension Plan | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	19.80%	16.00%
Employee Pension Plan | Fixed income | Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	5.00%
Employee Pension Plan | Fixed income | Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	45.00%
Employee Pension Plan | Company stock
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	15.10%	15.30%
Employee Pension Plan | Company stock | Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	0.00%
Employee Pension Plan | Company stock | Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	15.00%
Employee Pension Plan | Other assets
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	6.20%	14.40%
Employee Pension Plan | Other assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	0.00%
Employee Pension Plan | Other assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Targeted Allocation Range	20.00%
Postretirement Plan | Diversified investment funds
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	98.20%	97.70%
Postretirement Plan | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	1.80%	2.30%