Shareholders' Equity - Changes in Certain Components of Shareholders' Equity (Detail II) - $ / shares	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Stockholders' Equity Note [Abstract]
Common stock dividend per share (USD per share)	$ 2.92	$ 2.64	$ 2.40

Aggregate dividends paid during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration