Benefit Plans - Pension Plans with Accumulated Benefit Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Retirement Benefits [Abstract]
Accumulated benefit obligation exceeds the fair value of plan assets, projected benefit obligation	$ 3,623	$ 2,618
Accumulated benefit obligation exceeds the fair value of plan assets, accumulated benefit obligation	3,476	2,533
Accumulated benefit obligation exceeds the fair value of plan assets, fair value of plan assets	2,821	2,012
Projected benefit obligation exceeds the fair value of plan assets, projected benefit obligation	3,698	3,121
Projected benefit obligation exceeds the fair value of plan assets, fair value of plan assets	$ 2,882	$ 2,502

No definition available.

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

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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