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Retirement and Postretirement Employee Benefit Plans - Actuarial Assumptions For Net Periodic Pension Cost (Details) - Postretirement Plan | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate pension asset | 5.47% | 5.01% |
Discount rate postretirement cost | 5.01% | 6.06% | 5.61%
Expected return on plan assets pension asset | 5.14% | 5.14% |
Expected return on plan assets postretirement cost | 5.14% | 4.94% | 4.94%
Initial trend rate pension asset | 7.00% | 6.75% |
Initial trend rate postretirement cost | 6.75% | 6.50% | 6.25%
Ultimate trend rate pension asset | 5.00% | 5.00% |
Ultimate trend rate postretirement cost | 5.00% | 5.00% | 4.75%

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- Definition Defined Benefit Plan, Assumptions Used Calculating Benefit Asset, Discount Rate + References No definition available. + Details
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- Definition Defined Benefit Plan, Assumptions Used Calculating Benefit Asset, Expected Long-term Return on Assets + References No definition available. + Details
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- Definition Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Benefit Asset + References No definition available. + Details
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- Definition The ultimate trend rate for health care costs. + References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(1) -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 (k)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(3) -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 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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