CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par	Accumulated Deficit	Air Products’ Net Investment	Accumulated Other Comprehensive Income (Loss)	Total Versum’s Stockholders’ Equity (Deficit)	Non-controlling Interests
Stockholders' equity, beginning balance at Sep. 30, 2015	$ 740.7				$ 741.5	$ (32.8)	$ 708.7	$ 32.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	172.9				166.8		166.8	6.1
Net transfers to Air Products	(152.4)				(153.3)		(153.3)	0.9
Other comprehensive income (loss)	15.6					15.7	15.7	(0.1)
Share-based compensation	3.4				3.4		3.4
Dividends to non-controlling interests	(6.0)							(6.0)
Stockholders' equity, ending balance at Jun. 30, 2016	774.2				758.4	(17.1)	741.3	32.9
Stockholders' equity, beginning balance at Sep. 30, 2016	(103.4)	$ 0.0	$ 0.0	$ 0.0	(127.3)	(10.0)	(137.3)	33.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	153.8			148.4			148.4	5.4
Net transfers to Air Products	(158.1)			(291.5)	135.4	(2.1)	(158.2)	0.1
Reclassification of Air Products' net investment to additional paid in capital			8.1		(8.1)
Cash dividend paid	(5.4)		(5.4)				(5.4)
Issuance of common stock at separation	108.7	108.7					108.7
Issuance of common stock through shared based compensation plans	0.1	0.1					0.1
Other comprehensive income (loss)	(8.9)					(10.1)	(10.1)	1.2
Share-based compensation	4.7		4.7				4.7
Dividends to non-controlling interests	(1.2)							(1.2)
Stockholders' equity, ending balance at Jun. 30, 2017	$ (9.7)	$ 108.8	$ 7.4	$ (143.1)	$ 0.0	$ (22.2)	$ (49.1)	$ 39.4