Cash Flows - Actual Employer Contributions (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	$ 16	$ 10
Expected employer contributions
Expected employer contributions 2016	9
Expected benefit payments
Expected benefit payments 2016	146
Expected benefit payments 2017	92
Expected benefit payments 2018	94
Expected benefit payments 2019	93
Expected benefit payments 2020	93
Expected benefit payments 2021-2025	462
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	3	$ 4
Expected employer contributions
Expected employer contributions 2016	3
Expected benefit payments
Expected benefit payments 2016	3
Expected benefit payments 2017	3
Expected benefit payments 2018	3
Expected benefit payments 2019	3
Expected benefit payments 2020	2
Expected benefit payments 2021-2025	$ 5

The increase in the fair value of plan assets from contributions made by the employer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References