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Benefit Plans Sensitivity to Certain Changes in Pension Assumptions (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	25.00%
Discount rate
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 17,000,000
Impact on Projected Benefit Obligation	$ 418,000,000
Rate of return on plan assets
Defined Benefit Plan Disclosure
Change in Assumption	(0.25%)
Impact on Pension Cost	$ 18,000,000
Cost of Living Adjustments [Domain]
Defined Benefit Plan Disclosure
Change in Assumption	0.25%
Impact on Pension Cost	$ 30,000,000
Impact on Projected Benefit Obligation	$ 270,000,000
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Discount rate	3.05%	3.30%
Actuarial assumption COLA	$ 1.54	$ 0.0221	$ 0.0184
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
COLA percentage increase (decrease)	600.00%
Discount rate	2.75%	3.20%	4.35%
Pre-Medicare Eligible [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%	5.00%

X

- Definition

Actuarial assumption COLA

+ References

No definition available.

+ Details

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X

- Definition

COLA percentage increase (decrease)

+ References

No definition available.

+ Details

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X

- Definition

The change in the discount date or the rate of return on plan assets assumption that is used in disclosure of sensitivity of the net periodic pension cost and the projected benefit obligation to changes in those rates.

+ References

No definition available.

+ Details

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X

- Definition

The cost of living adjustment percentage used for defined benefit plans.

+ References

No definition available.

+ Details

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X

- Definition

Amount of effect of change in rate on the net periodic benefit cost for pension benefits.

+ References

No definition available.

+ Details

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X

- Definition

Amount of effect of change in rate on the projected benefit obligation for pension benefits.

+ References

No definition available.

+ Details

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X

- 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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X

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement 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 (l)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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