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Retirement and Postretirement Employee Benefit Plans - Asset Allocation (Details) | Sep. 30, 2025 | Sep. 30, 2024
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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%

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