Benefit Plans - Changes in Benefit Obligation for Postemployment Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Change in benefit obligation:
Beginning obligation	$ 184	$ 186
Service cost	18	20	$ 22
Interest cost	6	7	6
Benefits paid	(25)	(30)
Actuarial (gain) loss	(22)	1
Benefit obligation at September 30	$ 163	$ 184	$ 186

Changes in Post Employment Benefit Obligation [Abstract]

No definition available.

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- Definition

Amount of gain (loss) from a change in the postemployment benefit obligation from changes in actuarial assumptions.

+ References

No definition available.

+ Details

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- Definition

The amount of payments made for which participants are entitled under a postemployment plan.

+ References

No definition available.

+ Details

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- Definition

The increase in the postemployment plan's projected benefit obligation due to the passage of time.

+ References

No definition available.

+ Details

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- Definition

The actuarial present value of benefits attributed by the postemployment benefit formula to services rendered by employees during the period. The portion of the expected postemployment benefit obligation attributed to employee service during the period.

+ References

No definition available.

+ Details

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- Definition

The carrying amount as of the balance sheet date of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 712

-SubTopic 10

-Section 25

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79691-111665

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 712

-SubTopic 10

-Section 25

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79708-111665

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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