The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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

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-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

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The ultimate trend rate for health care costs.

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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The amount of the cost recognized during the period for defined contribution plans.

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Defined Benefit Plan Contribution Percent Of Compensation

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Defined Benefit Plan, Postretirement Benefit Termination Age

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Pension, Postretirement and Other Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cash balance formula contributions, rate of eligible compensation	6.00%
Postretirement benefit plan, age when benefits terminate	65 years
Assumed annual rate of future increases in health benefits for the other postretirement benefits plan for fiscal 2011	8.00%
Assumed annual rate of future decreases in health benefits for the other postretirement benefits plan by 2017	5.00%
Increasing or decreasing the healthcare cost trend by one per cent would increase decrease the postretirement accumulated plan benefit obligation by less than	$ 1
Target allocation for plan assets, other	7.00%
Defined contribution plan, personnel costs	$ 49	$ 46	$ 44
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation for plan assets, equity securities, minimum	50.00%
Target allocation for plan assets, equity securities, maximum	80.00%
Plan asset allocation, equity securities	66.00%
Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation for plan assets, equity securities, minimum	25.00%
Target allocation for plan assets, equity securities, maximum	35.00%
Plan asset allocation, equity securities	33.00%
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan asset allocation, equity securities	1.00%