Basis of Presentation and Major Accounting Policies (Policies)	9 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying Consolidated Financial Statements are presented on a consolidated basis and include all of the accounts and operations of Versum and its majority-owned subsidiaries. The financial statements reflect the financial position, results of operations and cash flows of Versum in accordance with generally accepted accounting principles in the United States of America ("GAAP") for interim financial information.
Consolidation	The financial statements are unaudited and should be read in conjunction with the Annual Consolidated Financial Statements presented in the company's Annual Report on Form 10-K for our fiscal year ended September 30, 2018. The financial statements reflect all adjustments that, in the opinion of management, are necessary for a fair statement of the results of the interim periods presented; all adjustments have been included to provide a fair statement of the results for the reporting periods presented. All significant inter-company accounts and transactions have been eliminated. The results of operations for the three and nine months ended June 30, 2019 are not necessarily indicative of the results of operations for the full year.
Estimates and Assumptions	Estimates and Assumptions The Consolidated Financial Statements have been prepared in conformity with GAAP, using management’s best estimates and judgments where appropriate. These estimates and judgments affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. The estimates and judgments will also affect the reported amounts for certain revenues and expenses during the reporting period. Actual results could differ materially from these estimates and judgments.

Versum Materials, Inc. 10-Q