Pension and Retirement Plans - Defined Benefit Plan, Plan with Projected Benefit Obligation in Excess of Plan Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Pension Plan
Schedule Of Retirement Plans [Line Items]
Accumulated benefit obligation	$ 1,758	$ 331
Projected benefit obligation	1,806	344
Fair value of plan assets	1,595	149
Fair value of plan assets	1,607	163
Postretirement Benefits
Schedule Of Retirement Plans [Line Items]
Projected benefit obligation	48	56
Fair value of plan assets	$ 24	$ 26

Schedule Of Retirement Plans [Line Items]

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- Definition

Amount of plan asset for defined benefit pension plan with projected benefit obligation in excess of plan assets.

+ References

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- Definition

Amount of projected benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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- Definition

Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-3

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- Definition

Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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