ANNUAL COMBINED COMPREHENSIVE INCOME STATEMENTS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 219.9	$ 191.2	$ 130.7
Other Comprehensive Income (Loss), net of tax
Translation adjustments, net of tax of $0, $0.7, and $0	22.8	(48.4)	(3.9)
Total Other Comprehensive Income (Loss)	22.8	(48.4)	(3.9)
Comprehensive Income	242.7	142.8	126.8
Net Income Attributable to Non-controlling Interests	7.9	7.1	7.1
Other Comprehensive Loss Attributable to Non-controlling Interests	0.0	(2.1)	(0.9)
Comprehensive Income Attributable to Versum	$ 234.8	$ 137.8	$ 120.6