Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Millions	6 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill
Balance at beginning of period	$ 1,077.7
Acquisition of business	6.8
Translation	19.8
Balance at end of period	1,104.3
Architecture & Software [Member]
Goodwill
Balance at beginning of period	417.2
Acquisition of business	6.8
Translation	5.0
Balance at end of period	429.0
Control Products & Solutions [Member]
Goodwill
Balance at beginning of period	660.5
Acquisition of business	0.0
Translation	14.8
Balance at end of period	$ 675.3