EMPLOYEE BENEFIT PLANS - WEIGHTED AVERAGE ASSUMPTIONS (Details)	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Represented
Obligations:
Compensation increase		3.00%	3.00%
Nonrepresented
Obligations:
Compensation increase		3.50%	3.50%
Pension
Benefit costs:
Expected asset return	6.75%	7.25%	7.00%
Pension \| Represented
Benefit costs:
Discount rate	2.95%	3.37%	4.36%
Compensation increase	3.00%	3.00%	3.25%
Obligations:
Discount rate	3.10%	2.95%	3.37%
Compensation increase	3.00%	3.00%	3.00%
Pension \| Nonrepresented
Benefit costs:
Discount rate	2.92%	3.35%	4.35%
Compensation increase	3.50%	3.50%	3.50%
Obligations:
Discount rate	3.07%	2.92%	3.35%
Compensation increase	3.50%	3.50%	3.50%
OPEB
Benefit costs:
Expected asset return	6.75%	7.25%	7.00%
OPEB \| Represented
Benefit costs:
Discount rate	3.08%	3.48%	4.38%
Compensation increase	3.00%	3.00%	3.25%
Obligations:
Discount rate	3.24%	3.08%	3.48%
Compensation increase	3.00%
OPEB \| Nonrepresented
Benefit costs:
Discount rate	3.03%	3.44%	4.37%
Compensation increase	3.50%	3.50%	3.50%
Obligations:
Discount rate	3.17%	3.03%	3.44%
Compensation increase	3.50%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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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

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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.

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

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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

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