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Retirement Plan and Other Post-Retirement Benefits - Schedule of Health Care Cost Trend Rates (Details) | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Retirement Benefits [Abstract] |  |  |  |  |  |
Rate of Medical Cost Increase for Pre Age 65 Participants | 7.25% | [1] | 6.25% | [2] | 6.25% | [3]
Rate of Medical Cost Increase for Post Age 65 Participants | 5.75% | [1] | 5.75% | [2] | 5.00% | [3]
Annual Rate of Increase in the Per Capita Cost of Covered Prescription Drug Benefits | 11.75% | [1] | 10.25% | [2] | 6.85% | [3]
Annual Rate of Increase in the Per Capita Medicare Part B Reimbursement | 5.75% | [1] | 5.75% | [2] | 5.00% | [3]
Annual Rate of Increase in the Per Capita Medicare Part D Subsidy | 4.00% | [1] | 4.00% | [2] | 6.60% | [3]
Ultimate health care trend rate | 4.00% |  | 4.00% |  | 4.00% |
[1] | It was assumed that this rate would gradually decline to 4% by 2050.
[2] | It was assumed that this rate would gradually decline to 4% by 2049.
[3] | It was assumed that this rate would gradually decline to 4% by 2048.

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- Definition Estimated Gross Other Post Retirement Benefit Payments Rate Of Increase For Post Age Sixty Five Participants + References No definition available. + Details
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- Definition Ultimate trend rate for health care cost for defined benefit postretirement plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (k) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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