Document and Entity Information
| Document and Entity Information | Oct. 07, 2019 |
| Cover [Abstract] | |
| Title of 12(b) Security | Common Stock, par value $1.00 per share |
| Current Fiscal Year End Date | --09-30 |
| Amendment Flag | false |
| Entity Central Index Key | 0001660690 |
| Document Type | 8-K |
| Document Period End Date | Oct. 7, 2019 |
| Entity Registrant Name | Versum Materials, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 1-37664 |
| Entity Tax Identification Number | 47-5632014 |
| Entity Address, Address Line One | 8555 South River Parkway |
| Entity Address, City or Town | Tempe |
| Entity Address, State or Province | AZ |
| Entity Address, Postal Zip Code | 85284 |
| City Area Code | 602 |
| Local Phone Number | 282-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Trading Symbol | VSM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |