Business Segment Information - Sales and Operating Results of Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Sales and operating results of reportable segments
Sales	$ 1,586.6	$ 1,490.3
Income before income taxes	297.8	257.6
Interest expense	(20.0)	(18.7)
Third-party advisory fees	11.2
Operating Segments [Member]
Sales and operating results of reportable segments
Income before income taxes	355.5	316.6
Segment Reconciling Items [Member]
Sales and operating results of reportable segments
Purchase accounting depreciation and amortization	(4.4)	(5.6)
Non-operating pension costs	(5.9)	(19.8)
Costs related to unsolicited Emerson proposals	(11.2)	0.0
Interest expense	(20.0)	(18.7)
Corporate, Non-Segment [Member]
Sales and operating results of reportable segments
General corporate – net	(16.2)	(14.9)
Architecture & Software [Member]
Sales and operating results of reportable segments
Sales	746.9	696.4
Income before income taxes	224.6	208.6
Control Products & Solutions [Member]
Sales and operating results of reportable segments
Sales	839.7	793.9
Income before income taxes	$ 130.9	$ 108.0