CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net (Loss) Income	$ (85.2)	$ 64.1	$ 29.0	$ 148.1
Other Comprehensive (Loss) Income, net of tax
Translation adjustments	(5.1)	(23.3)	(11.1)	3.0
Gain from hedging activities	0.0	0.1	0.0	0.2
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0.0	0.4	(0.1)	0.4
Total Other Comprehensive (Loss) Income	(5.1)	(23.6)	(11.0)	2.8
Comprehensive (Loss) Income	(90.3)	40.5	18.0	150.9
Net Income Attributable to Non-controlling Interests	1.5	0.8	4.2	4.5
Other Comprehensive Loss Attributable to Non-controlling Interests	(0.2)	(1.6)	(0.5)	0.0
Comprehensive (Loss) Income Attributable to Versum	$ (91.6)	$ 41.3	$ 14.3	$ 146.4