Restructuring and related charges - Summarization of Remaining Accrual Balance Associated with Initiatives and Activity (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Restructuring Reserve [Roll Forward]
Non-Cash Items	$ (6.4)	$ (20.1)	$ (9.2)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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