Retirement and Postretirement Employee Benefit Plans - Asset Allocation (Details)	Sep. 30, 2024	Sep. 30, 2023
Employee Pension Plan | Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	42.80%	42.90%
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	15.80%	16.00%
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	22.30%	19.80%
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	16.70%	15.10%
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	2.40%	6.20%
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	97.80%	98.20%
Postretirement Plan | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	2.20%	1.80%