Benefit Plans - Weighted Average Assumptions Determining Pension Plan Footnote (Detail)	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Postemployment benefits, discount rate	3.75%	3.75%	4.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rates	3.95%	3.85%	4.40%

The interest rate used to adjust for the time value of money for the plan.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(1)

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

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