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EMPLOYEE BENEFIT PLANS - WEIGHTED AVERAGE ASSUMPTIONS (Details) | 12 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Pension |  |  |
Benefit costs: |  |  |
Expected asset return | 7.00% | 7.00% | 6.75%
Pension | Represented |  |  |
Benefit costs: |  |  |
Discount rate | 5.89% | 5.50% | 3.10%
Compensation increase | 3.00% | 3.00% | 3.00%
Obligations: |  |  |
Discount rate | 5.01% | 5.89% | 5.50%
Compensation increase | 3.00% | 3.00% | 3.00%
Pension | Nonrepresented |  |  |
Benefit costs: |  |  |
Discount rate | 5.87% | 5.50% | 3.07%
Compensation increase | 3.50% | 3.50% | 3.50%
Obligations: |  |  |
Discount rate | 4.99% | 5.87% | 5.50%
Compensation increase | 3.50% | 3.50% | 3.50%
OPEB |  |  |
Benefit costs: |  |  |
Expected asset return | 7.00% | 7.00% | 6.75%
OPEB | Represented |  |  |
Benefit costs: |  |  |
Discount rate | 5.97% | 5.51% | 3.24%
Compensation increase | 3.00% | 3.00% | 3.00%
Obligations: |  |  |
Discount rate | 4.97% | 5.97% | 5.51%
Compensation increase | 3.00% | 3.00% | 3.00%
OPEB | Nonrepresented |  |  |
Benefit costs: |  |  |
Discount rate | 5.94% | 5.51% | 3.17%
Compensation increase | 3.50% | 3.50% | 3.50%
Obligations: |  |  |
Discount rate | 4.98% | 5.94% | 5.51%
Compensation increase | 3.50% | 3.50% | 3.50%

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation 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 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 increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + 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 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 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 2: 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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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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