Benefit Plans - Pension Plans with Accumulated Benefit Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Accumulated benefit obligation exceeds the fair value of plan assets, accumulated benefit obligation	$ 3,309	$ 3,703
Accumulated benefit obligation exceeds the fair value of plan assets, fair value of plan assets	2,712	2,936
Projected benefit obligation exceeds the fair value of plan assets, projected benefit obligation	3,475	3,920
Projected benefit obligation exceeds the fair value of plan assets, fair value of plan assets	$ 2,780	$ 2,996

No definition available.

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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
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-Publisher FASB
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2417-114920

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