Basis of Presentation	12 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	1.BASIS OF PRESENTATION In September 2016, Versum Materials, Inc. was formed and after its Separation from Air Products on October 1, 2016, Versum began operating as an independent public company and its common stock is listed under the symbol “VSM” on the New York Stock Exchange. We are a global business that provides innovative solutions for specific customer applications within niche markets based upon expertise in specialty materials. Our business employs applications technology to provide solutions to the semiconductor industry through chemical synthesis, analytical technology, process engineering, and surface science. We are comprised of two primary operating segments, Materials and Delivery Systems and Services, under which we manage our operations and assess performance, and a Corporate segment. Prior to the Separation, the accompanying Annual Consolidated Financial Statements of Versum, were prepared on a stand-alone basis and were derived from Air Products’ consolidated financial statements and accounting records where Versum was a division of Air Products. For all periods presented, the Annual Consolidated Financial Statements were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Versum. All significant intercompany transactions and balances have been eliminated in the preparation of the accompanying Annual Consolidated Financial Statements. Prior to the Separation, transactions between Versum and Air Products were reflected in the annual consolidated statements of cash flows as a financing activity in “Net transfers to Air Products.” Prior to the Separation, Air Products provided us with centrally managed services and corporate functions. Accordingly, certain shared costs including but not limited to administrative expenses for information technology, general services, human resources, legal, accounting and other services, had been allocated to us and were reflected as expenses in the Annual Consolidated Financial Statements. Expenses had been allocated on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed costs, revenue, operating income or headcount. We consider the expense allocation methodology and results to be reasonable and consistently applied for all periods presented prior to the Separation. After the Separation, Versum has performed most of these functions using its own resources or purchased services. However, the remainder of these functions continued to be provided by Air Products under various agreements. See Note 4, Related Party Transactions, for a description of the agreements between Versum and Air Products. For periods prior to October 1, 2016, included within our Annual Consolidated Financial Statements were the results of certain product lines which had historically been managed by us but were retained by Air Products after the Separation. These product lines represented approximately 1% and 1% of annual combined sales and operating income, respectively, for fiscal year 2016. For periods prior to the Separation, Versum’s income tax expense was calculated using the separate return method as if Versum was a separate taxpayer. The majority of the accrued U.S. federal, state, and foreign income tax balances were treated as settled with Air Products as of the end of each year. After the Separation, income tax expense and income tax balances represent Versum’s federal, state and foreign income taxes as an independent company.

1.BASIS OF PRESENTATION

In September 2016, Versum Materials, Inc. was formed and after its Separation from Air Products on October 1, 2016, Versum began operating as an independent public company and its common stock is listed under the symbol “VSM” on the New York Stock Exchange.

We are a global business that provides innovative solutions for specific customer applications within niche markets based upon expertise in specialty materials. Our business employs applications technology to provide solutions to the semiconductor industry through chemical synthesis, analytical technology, process engineering, and surface science. We are comprised of two primary operating segments, Materials and Delivery Systems and Services, under which we manage our operations and assess performance, and a Corporate segment.

Prior to the Separation, the accompanying Annual Consolidated Financial Statements of Versum, were prepared on a stand-alone basis and were derived from Air Products’ consolidated financial statements and accounting records where Versum was a division of Air Products. For all periods presented, the Annual Consolidated Financial Statements were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Versum. All significant intercompany transactions and balances have been eliminated in the preparation of the accompanying Annual Consolidated Financial Statements. Prior to the Separation, transactions between Versum and Air Products were reflected in the annual consolidated statements of cash flows as a financing activity in “Net transfers to Air Products.”

Prior to the Separation, Air Products provided us with centrally managed services and corporate functions. Accordingly, certain shared costs including but not limited to administrative expenses for information technology, general services, human resources, legal, accounting and other services, had been allocated to us and were reflected as expenses in the Annual Consolidated Financial Statements. Expenses had been allocated on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed costs, revenue, operating income or headcount. We consider the expense allocation methodology and results to be reasonable and consistently applied for all periods presented prior to the Separation.

After the Separation, Versum has performed most of these functions using its own resources or purchased services. However, the remainder of these functions continued to be provided by Air Products under various agreements. See Note 4, Related Party Transactions, for a description of the agreements between Versum and Air Products.

For periods prior to October 1, 2016, included within our Annual Consolidated Financial Statements were the results of certain product lines which had historically been managed by us but were retained by Air Products after the Separation. These product lines represented approximately 1% and 1% of annual combined sales and operating income, respectively, for fiscal year 2016.

For periods prior to the Separation, Versum’s income tax expense was calculated using the separate return method as if Versum was a separate taxpayer. The majority of the accrued U.S. federal, state, and foreign income tax balances were treated as settled with Air Products as of the end of each year. After the Separation, income tax expense and income tax balances represent Versum’s federal, state and foreign income taxes as an independent company.