CONSOLIDATED INCOME STATEMENTS (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues	$ 324.3	$ 350.0	$ 990.0	$ 1,021.5
Cost of sales	185.6	200.3	571.5	587.3
Selling and administrative	34.5	35.2	102.6	107.0
Research and development	11.9	12.4	35.9	36.2
Business separation, restructuring and cost reduction actions	141.4	6.7	156.3	16.7
Other (income) expense, net	(1.6)	(0.9)	(7.2)	(0.9)
Operating Income (Loss)	(47.5)	96.3	130.9	275.2
Interest expense	13.0	12.5	39.0	35.7
Gain (Loss) on Extinguishment of Debt	0.0	0.0	0.0	2.1
Non-service components of net periodic pension costs	0.2	0.1	0.6	0.5
(Loss) Income Before Taxes	(60.7)	83.7	91.3	236.9
Income tax provision	24.5	19.6	62.3	88.8
Net (Loss) Income	(85.2)	64.1	29.0	148.1
Less: Net Income Attributable to Non-Controlling Interests	(1.5)	(0.8)	(4.2)	(4.5)
Net (Loss) Income Attributable to Versum	$ (86.7)	$ 63.3	$ 24.8	$ 143.6
Net (Loss) income attributable to Versum per common share:
Basic (usd per share)	$ (0.79)	$ 0.58	$ 0.23	$ 1.32
Diluted (usd per share)	$ (0.79)	$ 0.58	$ 0.23	$ 1.31
Shares used in computing per common share amounts:
Basic (shares)	109.2	108.9	109.1	108.9
Diluted (shares)	109.2	109.8	110.0	109.7