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Retirement and Postretirement Employee Benefit Plans - Asset Allocation (Details)	Sep. 30, 2025	Sep. 30, 2024
Employee Pension Plan \| Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	43.60%	42.80%
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	15.50%	15.80%
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	24.30%	22.30%
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	14.00%	16.70%
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	2.60%	2.40%
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	98.60%	97.80%
Postretirement Plan \| Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	1.40%	2.20%