Versum Materials (VSM) 10-Q 7 May 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Apr. 26, 2019
Document and Entity Information [Abstract]
Entity Registrant Name		Versum Materials, Inc.
Entity Central Index Key		0001660690
Current Fiscal Year End Date		--09-30
Entity Filer Category		Large Accelerated Filer
Document Type		10-Q
Document Period End Date		Mar. 31, 2019
Document Fiscal Year Focus		2019
Document Fiscal Period Focus		Q2
Amendment Flag		false
Entity Common Stock, Shares Outstanding			109,240,997
Entity Small Business	false
Entity Emerging Growth Company	false

CONSOLIDATED INCOME STATEMENTS

CONSOLIDATED INCOME STATEMENTS (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenues	$ 326.2	$ 340.7	$ 665.7	$ 671.5
Cost of sales	189.8	195.8	385.9	387
Selling and administrative	32.6	36.5	68.1	71.8
Research and development	11.1	11.1	24	23.8
Business separation, restructuring and cost reduction actions	13.8	8.2	14.9	10
Other (income) expense, net	(3.7)	(0.5)	(5.6)	0
Operating Income (Loss)	82.6	89.6	178.4	178.9
Interest expense	13.2	11.9	26	23.2
Gain (Loss) on Extinguishment of Debt	0	0	0	2.1
Non-service components of net periodic pension costs	0.2	0.2	0.4	0.4
Income Before Taxes	69.2	77.5	152	153.2
Income tax provision	18.1	14.2	37.8	69.2
Net Income	51.1	63.3	114.2	84
Less: Net Income Attributable to Non-Controlling Interests	0.7	1.7	2.7	3.7
Net Income Attributable to Versum	$ 50.4	$ 61.6	$ 111.5	$ 80.3
Net income attributable to Versum per common share:
Basic (usd per share)	$ 0.46	$ 0.57	$ 1.02	$ 0.74
Diluted (usd per share)	$ 0.46	$ 0.56	$ 1.01	$ 0.73
Shares used in computing per common share amounts:
Basic (shares)	109.1	108.9	109.1	108.9
Diluted (shares)	110	109.7	109.9	109.8

CONSOLIDATED COMPREHENSIVE INCO

CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 51.1	$ 63.3	$ 114.2	$ 84
Other Comprehensive Income (Loss), net of tax
Translation adjustments	(6.9)	6.6	(6)	26.3
Gain from hedging activities	0	0	0	0.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(0.1)	0	(0.1)	0
Total Other Comprehensive Income (Loss)	(6.8)	6.6	(5.9)	26.4
Comprehensive Income	44.3	69.9	108.3	110.4
Net Income Attributable to Non-controlling Interests	0.7	1.7	2.7	3.7
Other Comprehensive Income (Loss) Attributable to Non-controlling Interests	(0.3)	0.9	(0.3)	1.6
Comprehensive Income Attributable to Versum	$ 43.9	$ 67.3	$ 105.9	$ 105.1

CONSOLIDATED BALANCE SHEETS (Un

CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Current Assets
Cash and cash items	$ 390.8	$ 399.8
Short-term Investments	11.4	0
Trade receivables, net	188.1	184.4
Inventories	203.1	177.1
Contracts in progress, less progress billings	32	20.3
Prepaid expenses	21.1	13.6
Other current assets	19.3	17.9
Total Current Assets	865.8	813.1
Plant and equipment:
Plant and equipment, at cost	1,105.7	1,072.1
Less: accumulated depreciation	683.4	667
Plant and equipment, net	422.3	405.1
Goodwill	182.5	183
Intangible assets, net	60.7	63.5
Other noncurrent assets	35.9	40.6
Total Noncurrent Assets	701.4	692.2
Total Assets	1,567.2	1,505.3
Current Liabilities
Payables and accrued liabilities	122.8	138.6
Accrued income taxes	35.4	43.3
Short-term Debt	0.3	0
Current portion of long-term debt	5.8	5.8
Total Current Liabilities	164.3	187.7
Long-term debt	972.2	974.2
Noncurrent income tax payable	32.3	37.3
Deferred tax liabilities	38.9	41.3
Other noncurrent liabilities	53.6	52.4
Total Noncurrent Liabilities	1,097	1,105.2
Total Liabilities	1,261.3	1,292.9
Commitments and Contingencies - See Note 15
Stockholders’ Equity
Common stock (par value $1 per share; 250,000,000 shares authorized; outstanding 109,232,063 and 108,951,596 at March 31, 2019 and September 30, 2018, respectively)	109.2	109
Capital in excess of par	8.7	6.1
Retained earnings	175.5	81.6
Accumulated other comprehensive loss	(23.8)	(18.2)
Total Versum’s Stockholders’ Equity	269.6	178.5
Non-controlling Interests	36.3	33.9
Total Stockholders’ Equity	305.9	212.4
Total Liabilities and Stockholders’ Equity	$ 1,567.2	$ 1,505.3

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (Unaudited) (Parentheticals) - $ / shares	Mar. 31, 2019	Sep. 30, 2018
Statement of Financial Position [Abstract]
Common stock, par value (usd per share)	$ 1	$ 1
Common stock, shares authorized (shares)	250,000,000	250,000,000
Common stock, shares outstanding (shares)	109,232,063	108,951,596

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities
Net income	$ 114.2	$ 84
Less: Net Income Attributable to Non-Controlling Interests	2.7	3.7
Net Income Attributable to Versum	111.5	80.3
Adjustments to reconcile income to cash provided by operating activities:
Depreciation and amortization	27.2	23.9
Deferred income taxes	(0.9)	(4.4)
Gain on sale of assets	0	(0.3)
Share-based compensation	5.2	5
Other adjustments	8.8	(1.2)
Working capital changes that provided (used) cash:
Trade receivables	(5.7)	(16.9)
Inventories	(27.2)	(10.8)
Contracts in progress, less progress billings	(11.7)	(18)
Payables and accrued liabilities	(11.8)	(46.4)
Accrued income taxes	(18.2)	39.2
Other working capital	(3.9)	6.1
Cash Provided by Operating Activities	73.3	56.5
Investing Activities
Additions to plant and equipment	(45)	(65.1)
Proceeds from sale of assets	0.7	1
Payments to Acquire Short-term Investments	11.4	0
Cash Used for Investing Activities	(55.7)	(64.1)
Financing Activities
Payments on long-term debt	(2.9)	(2.9)
Proceeds from Short-term Debt	0.3	0
Dividends paid to shareholders	(17.6)	(10.9)
Other financing activity	(4.9)	(2.8)
Cash Used for Financing Activities	(25.1)	(16.6)
Effect of Exchange Rate Changes on Cash	(1.5)	7.2
Increase (Decrease) in Cash and Cash Items	(9)	(17)
Cash and Cash items-Beginning of Year	399.8	271.4
Cash and Cash items-End of Period	390.8	254.4
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	24.7	21.8
Income Taxes Paid	$ 58.3	$ 37

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Total Versum’s Stockholders’ Equity (Deficit)	Non-controlling Interests
Stockholders' equity, beginning balance at Sep. 30, 2017	$ 30.2	$ 108.8	$ 4.8	$ (99.6)	$ (18.4)	$ (4.4)	$ 34.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84			80.3		80.3	3.7
Cash dividend paid	(10.9)		(7.7)	(3.2)		(10.9)
Issuance of common stock through shared based compensation plans	0.1	0.1				0.1
Other comprehensive loss	26.4				24.8	24.8	1.6
Share-based compensation	2.9		2.9			2.9
Stockholders' equity, ending balance at Mar. 31, 2018	132.7	108.9	0	(22.5)	6.4	92.8	39.9
Stockholders' equity, beginning balance at Sep. 30, 2018	212.4	109	6.1	81.6	(18.2)	178.5	33.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	114.2			111.5		111.5	2.7
Cash dividend paid	(17.6)		0	(17.6)		(17.6)
Issuance of common stock through shared based compensation plans	0.2	0.2				0.2
Other comprehensive loss	(5.9)				(5.6)	(5.6)	(0.3)
Share-based compensation	2.6		2.6			2.6
Stockholders' equity, ending balance at Mar. 31, 2019	$ 305.9	$ 109.2	$ 8.7	$ 175.5	$ (23.8)	$ 269.6	$ 36.3

Basis of Presentation and Major

Basis of Presentation and Major Accounting Policies	6 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Major Accounting Policies	BASIS OF PRESENTATION AND MAJOR ACCOUNTING POLICIES Versum is 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 operating segments, Materials and Delivery Systems and Services, under which we manage our operations and assess performance, and a Corporate segment. Versum’s common stock is listed under the symbol “VSM” on the New York Stock Exchange. 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. 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 six months ended March 31, 2019 are not necessarily indicative of the results of operations for the full year. Accounting Policies The policies used in preparing the Consolidated Financial Statements are the same as those used in our Annual Report on Form 10-K for our fiscal year ended September 30, 2018 . Other than our adoption of a new revenue recognition policy which did not have a material impact on the Consolidated Financial Statements, there have been no significant changes to these accounting policies during the three and six months ended March 31, 2019 . See Note 3 , Revenue from Contracts with Customers , for a discussion on the impacts of the new revenue recognition policy on our Consolidated Financial Statements. 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.

New Accounting Guidance

New Accounting Guidance	6 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
New Accounting Guidance	NEW ACCOUNTING GUIDANCE Accounting Guidance Implemented Income Taxes In March 2018, the Financial Accounting Standards Board (“FASB”) issued guidance relative to Incomes Taxes (Topic 740) that adds various Securities and Exchange Commission (“SEC”) paragraphs pursuant to the issuance of the December 2017 SEC Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”), which was effective immediately. The SEC issued SAB 118 to address concerns about reporting entities’ ability to timely comply with the accounting requirements to recognize all of the effects of the Tax Cuts and Jobs Act (the “Tax Act”) in the period of enactment. SAB 118 allows disclosure that timely determination of some or all of the income tax effects from the Tax Cuts and Jobs Act are incomplete by the due date of the financial statements and if possible to provide a reasonable estimate. Our accounting for income tax effects associated with the enactment of the Tax Act are complete and recorded in our Consolidated Financial Statements as of December 31, 2018. See Note 8 for further discussion. Net Periodic Pension Costs In March 2017, the FASB issued guidance which requires an entity to report the service cost component of pension expense in the same line item as other compensation costs. The other components of net (benefit) cost will be required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. This standard is effective for annual reporting periods beginning after December 15, 2017 and interim periods within those annual periods. The components of the net (benefit) cost are shown in Note 11 , Retirement Benefits . The company adopted the standard effective October 1, 2018. The adoption required us to reclassify amounts out of Operating Income. This resulted in a decrease to Cost of Sales of $0.1 million , a decrease of Selling and Administrative costs of $0.1 million and an increase to Operating Income of $0.2 million for the three month period ending March 31, 2018. For the six months ending March 31, 2018 Cost of Sales decreased by $0.3 million , Selling and Administrative costs decreased by $0.1 million and Operating Income increased by $0.4 million . No other financial statement line items were impacted. We do not consider this to be a material impact on the Consolidated Financial Statements. Business Combinations In January 2017, the FASB issued guidance on the definition of a business in business combinations. The guidance clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill, and consolidation. The guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those periods. The company adopted the standard effective October 1, 2018. The adoption did not have a material impact on the Consolidated Financial Statements. Revenue Recognition In May 2014, the FASB issued guidance based on the principle that revenue is recognized in an amount expected to be collected and to which the entity expects to be entitled in exchange for the transfer of goods or services. In August 2015, the FASB deferred the effective date by one year, while providing the option to early adopt the standard on the original effective date. In December 2016 there were further updates to the original guidance that did not revise the effective date. The company adopted the standard effective October 1, 2018. See Note 3 , Revenue from Contracts with Customers , for a discussion on the impacts on our Consolidated Financial Statements. Cash Flow Statement Classification In August 2016, the FASB issued guidance to reduce diversity in practice on how certain cash receipts and cash payments are classified in the statement of cash flows. The guidance is effective beginning fiscal year 2019, with early adoption permitted, and should be applied retrospectively. The company adopted the standard effective October 1, 2018. The adoption did not have a material impact on the Consolidated Financial Statements. New Accounting Guidance to be Implemented Leases In February 2016, with updates in July 2018 and January 2019, the FASB issued guidance which requires lessees to recognize a right of use asset and lease liability on the balance sheet for all leases, including operating leases, with a term in excess of 12 months. The guidance also expands the quantitative and qualitative disclosure requirements. The guidance is effective in fiscal year 2020, with early adoption permitted, and originally required to be applied using a modified retrospective approach. The company is currently the lessee under various agreements for distribution equipment, vehicles and buildings that are currently accounted for as operating leases. The new guidance requires the lessee to record operating leases on the balance sheet with a right-of-use asset and corresponding liability for future payment obligations. The company will adopt the standard effective October 1, 2019. We are currently evaluating the impact of adopting this new guidance on our Consolidated Financial Statements.

Revenue from Contracts with Cus

Revenue from Contracts with Customers (Notes)	6 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	REVENUE FROM CONTRACTS WITH CUSTOMERS The company adopted ASC 606 on October 1, 2018 using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for the three and six months ended March 31, 2019 reflect the application of ASC 606 guidance while the reported results for 2018 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605). The company has determined the impact of ASC 606 on opening retained earnings was immaterial as of October 1, 2018. The impact to revenues for the three and six months ended March 31, 2019 was immaterial as a result of applying ASC 606. The adoption of ASC 606 represents a change in accounting principle that will more closely align revenue recognition with the delivery of the company's goods or services and will provide financial statement readers with enhanced disclosures. To achieve this core principle, the company applies the following five steps: • Identify the contract with a customer • Identify the performance obligations in the contract • Determine the transaction price • Allocate the transaction price to performance obligations in the contract • Recognize revenue when or as the company satisfies a performance obligation Revenue under ASC 606 is recognized when or as obligations under the terms of a contract with the company's customer have been satisfied and control has transferred to the customer. The majority of the company's performance obligations, and associated revenue, are transferred to customers at a point in time, generally upon shipment of a product to the customer or receipt of the product by the customer and without significant judgments. Installation services are not significant and are usually completed in a short period of time and therefore, recorded at a point in time when the installation services are completed, rather than over time as they are not material. Service contracts, which are transferred to the customer over time, are recorded as revenue as the services are performed. Customized equipment with no alternative future use to the company, and that have an enforceable right to payment for performance completed to date, are also recorded over time. The company considers this to be a faithful depiction of the transfer to the customer of revenue over time as the work or service is performed. Revenue is measured as the amount of consideration the company expects to receive in exchange for transferring goods or providing services. Performance obligations promised in a contract are identified based on the products or services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the product or service either on its own or together with other resources that are readily available from third parties or from the company, and are distinct in the context of the contract, whereby the transfer of the product or service is separately identifiable from other promises in the contract. Sales, value add, and other taxes the company collects concurrent with revenue-producing activities are excluded from revenue. The company's normal payment terms vary by the type and location of its customers and the products or services offered. The time between invoicing and when payment is due is not significant. None of the company's contracts as of March 31, 2019 contain a significant financing component. The company does not disclose information about remaining performance obligations that have original expected durations of one year or less. Costs to Obtain and Fulfill a Contract The company recognizes the incremental costs of obtaining contracts as an expense when incurred if the amortization period of the assets that the company otherwise would have recognized is one year or less. The incremental costs to obtain contracts was not material. In most transactions, we have no obligations to our customers after the date products are shipped, other than pursuant to warranty obligations. Our standard warranties provide assurance to customers that the goods as delivered are free from defect or within their provided specifications. Shipping and handling fees billed to customers, if any, are recognized as revenue. The related shipping and handling costs are recognized in cost of sales. Based on the nature of our business returns are not material. Shipping and handling costs associated with outbound freight after control over a product has transferred to a customer are accounted for as a fulfillment cost and are included in cost of sales. The company estimates its allowance for doubtful accounts. The company continuously monitors collections and payments from its customers and maintains a provision for estimated credit losses based upon its historical experience and any specific customer collection issues that it has identified. Disaggregation of Revenue We are comprised of two primary operating segments, Materials and Delivery Systems and Services (“DS&S”), under which we manage our operations and assess performance, and a Corporate segment. Our segments are differentiated by the types of product groups they sell. Materials The Materials operating segment is an integrated provider of specialty materials for the high-growth electronics industry, focusing on the integrated circuit and flat-panel display markets. This segment provides the global semiconductor industry with high purity process materials for deposition, metallization, chamber cleaning and etching, chemicals mechanical planarization slurries, organosilanes, organometallics and liquid dopants for thin film deposition, and formulated chemical products for post-etch cleaning primarily for the manufacture of silicon and compound semiconductors and thin film transistor liquid crystal displays. The Materials segment is further divided into two main product groups. • Advanced Materials (“AM”) - AM supplies products and services through three key product platforms that are employed in the fabrication of ICs. Advanced deposition materials products include high purity specialty gases and chemicals, such as organosilane and organometallic precursors that are used to deposit thin films which comprise an IC. Planarization products include chemical mechanical planarization (“CMP”) slurries and post CMP cleans that are used to prepare chips with deposited thin films for the next stage of fabrication. Surface prep and clean formulated products are designed to selectively etch and remove debris and contamination during multiple stages of the wafer fabrication process including advanced packaging. • Process Materials (“PM”) - PM supplies products such as high-purity gases and chemicals utilized in the processes of cleaning, etching, doping, and film deposition for our semiconductor, displays and light emitting diode customers. Given the nature of the Materials segment the majority of revenue is recognized at a point in time. DS&S The DS&S operating segment designs, manufactures, installs, operates, and maintains chemical and gas delivery and distribution systems for specialty gases and chemicals delivered directly to our customers’ manufacturing tools. In addition, the business provides turnkey installation services during facility construction and startup as well as onsite operating services. Below are the two product groups for DS&S. • Equipment and installation (Gas, chemical and slurry delivery systems) - DS&S develops, designs, manufactures and sells bulk gas, specialty gas and specialty chemical cabinets and systems that are critical to managing the delivery of key materials into the semiconductor manufacturing process. DS&S also offers resources to assist both new and refurbished semiconductor fabs in the design, installation, startup, and commissioning of the gases and specialty materials delivery systems and quality assurance. The scope of installation services includes project management for installation and startup of the gas and chemical delivery systems, and inventory management. Given the nature of equipment and installation services for DS&S the majority of the revenue is recognized at a point in time. • On-Site Services (MEGASYS): DS&S offers on-site contract services to assist customers in managing their inventory of gases and chemicals, including ordering, product changes and monitoring, quality assurance, operating our delivery systems, and managing the bulk gas and specialty gas operations. These services are typically performed on the customer site. Given the nature of the site services for DS&S the revenue is recognized over time. Corporate The Corporate segment includes certain administrative costs such as information technology, general services, human resources, legal, accounting, and other services, as well as foreign exchange gains and losses, and other income and expense that cannot be directly associated with operating segments. The company disaggregates its revenue from contracts with customers by product group, which it believes best depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. The following table summarizes revenue from contracts with customers disaggregated by product group: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Materials Advanced Materials $ 117.6 $ 119.4 $ 241.2 $ 231.3 Process Materials 98.9 99.5 197.0 202.2 Total Materials 216.5 218.9 438.2 433.5 DS&S Equipment and Installations 92.6 105.1 193.5 205.5 Site Services 16.5 16.0 32.8 30.9 Total DS&S 109.1 121.1 226.3 236.4 Corporate 0.6 0.7 1.2 1.6 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5 The following table summarizes revenue from contracts with customers related to the geographic area in which the company operates: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Sales to External Customers United States $ 96.5 $ 102.4 $ 196.6 $ 197.4 Taiwan 59.6 63.3 124.2 122.6 South Korea 111.1 112.7 227.1 231.2 China 19.4 26.8 38.6 47.8 Europe 16.3 15.0 32.0 30.5 Asia, excluding China, Taiwan, and South Korea 23.3 20.5 47.2 42.0 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5 Contract Balances The following tables provide information about contract assets and contract liabilities from contracts with customers. The contract assets primarily relate to our rights to consideration for products produced but not billed at the reporting date on contracts with certain customers. The contract assets are recognized as accounts receivables when the rights become unconditional and the customer has been billed. Contract liabilities represent obligations to transfer goods to a customer for which we have received consideration from our customer. A roll-forward of the company’s contracts in progress, less progress billings is as follows: Six Months Ended March 31, 2019 (In millions) Beginning balance (1) $ 20.3 Change related to revenue in excess of billings 11.7 Ending balance (1) $ 32.0 (1) Beginning and ending balances are current A roll-forward of the company’s deferred revenue is as follows: Six Months Ended March 31, 2019 (In millions) Beginning balance (1) $ 18.7 Amount of deferred revenue recognized in income (44.9 ) Additions to deferred revenue 32.6 Ending balance (1) $ 6.4 (1) Beginning and ending balances are current

Business Separation, Restructur

Business Separation, Restructuring, and Cost Reduction Actions	6 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Business Separation, Restructuring, and Cost Reduction Actions	BUSINESS SEPARATION, RESTRUCTURING AND COST REDUCTION ACTIONS The charges we record for business restructuring and cost reduction actions have been excluded from segment operating income. During the three and six months ended March 31, 2019 , we recognized a net charge of $13.8 million and $14.9 million , respectively. The net charge primarily consisted of costs associated with the previously planned merger with Entegris, Inc. (“Entegris”). During the three and six months ended March 31, 2018 , we recognized a net charge of $8.2 million and $10.0 million , respectively. The net charge primarily consisted of additional costs as a result of the relocation of certain research and development activities and our headquarters and set up of the stand-alone organization and infrastructure. The following table summarizes the carrying amount of the accrual for the business separation, restructuring and cost reduction actions at March 31, 2019 : Severance and Other Benefits (In millions) Balance, September 30, 2018 $ 3.2 Current Period Charge (0.3 ) Cash Payments (0.7 ) Balance, March 31, 2019 $ 2.2

Inventories

Inventories	6 Months Ended
	Mar. 31, 2019
Inventory Disclosure [Abstract]
Inventories	INVENTORIES The components of inventories are as follows: March 31, 2019 September 30, 2018 (In millions) Inventories at FIFO cost Finished goods $ 116.5 $ 104.3 Work in process 17.3 15.1 Raw materials, supplies and other 69.3 57.7 Inventories $ 203.1 $ 177.1 The September 30, 2018 inventory amounts have been adjusted for the company’s election to change its inventory valuation method of accounting for its U.S. inventories from the last-in, first-out (“LIFO”) method to the first-in, first-out (“FIFO”) method effective the fourth quarter of fiscal 2018. The cost for FIFO inventory approximates replacement cost.

Goodwill

Goodwill	6 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	GOODWILL Changes to the carrying amount of goodwill by segment are as follows: Materials Delivery Systems and Services Total (In millions) Balance, September 30, 2018 $ 165.6 $ 17.4 $ 183.0 Currency translation adjustment (0.4 ) (0.1 ) (0.5 ) Balance, March 31, 2019 $ 165.2 $ 17.3 $ 182.5 Goodwill is subject to impairment testing in the fourth quarter of each fiscal year and whenever events and changes in circumstances indicate that the carrying value of goodwill might not be recoverable. There were no events or circumstances indicating that goodwill might be impaired at March 31, 2019 .

Debt

Debt	6 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	DEBT Components of Debt March 31, 2019 September 30, 2018 (In millions) Short-term borrowings (A) $ 0.3 $ — Current portion of long-term debt 5.8 5.8 Long-term debt 972.2 974.2 Total Debt $ 978.3 $ 980.0 (A) Represents borrowing under foreign lines of credit by non-U.S. subsidiaries which are short term in nature. Availability under these lines of credit at March 31, 2019 was $19.9 million . Long-term debt March 31, 2019 September 30, 2018 (In millions) Term loan facility under Credit Agreement $ 560.6 $ 563.5 Revolving facility under Credit Agreement — — 5.5% Senior Notes due 2024 425.0 425.0 Total debt 985.6 988.5 Less debt discount 1.6 1.8 Less deferred debt costs 6.0 6.7 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 972.2 $ 974.2 Credit Agreement On September 30, 2016, Versum entered into a credit agreement (the “Credit Agreement”) providing for a senior secured first lien term loan B facility of $575 million (the “Term Facility”) and a senior secured first lien revolving credit facility of $200 million (the “Revolving Facility” and, together with the Term Facility, the “Senior Credit Facilities”). The Senior Credit Facilities are guaranteed by Versum’s material direct and indirect wholly-owned domestic restricted subsidiaries and secured by substantially all of the assets of Versum and its subsidiary guarantors. Borrowings under the Term Facility bore interest at a rate of either LIBOR (adjusted for statutory reserve requirements), subject to a minimum floor of 0.75% , plus a margin of 2.50% or an alternate base rate , subject to a minimum floor of 1.75% , plus a margin of 1.50% . On October 10, 2017, Versum amended its Credit Agreement. The amendment decreased the interest rate on borrowings under the Term Facility to LIBOR plus a margin of 2.00% , or an alternate base rate plus a margin of 1.00% (effective rate of 4.60% as of March 31, 2019 ). The amendment removed the minimum floor on LIBOR and the alternate base rate. If our total leverage ratio is equal to or less than 2.00 : 1.00 (calculated without any netting of cash on hand) the interest rate will decrease further to LIBOR plus a margin of 1.75% , or an alternate base rate plus a margin of 0.75% . The Term Facility matures on September 30, 2023 , and will amortize in equal quarterly installments in aggregate annual amounts equal to 1.00% of the original principal amount of the Term Facility, with the balance payable on September 30, 2023 . Borrowings under the Revolving Facility bear interest initially at a rate of either LIBOR (adjusted for statutory reserve requirements) plus a margin of 2.00% or an alternate base rate plus a margin of 1.00% , subject to a 0.25% margin reduction based on achieving a first lien net leverage ratio of 1.00 :1.00. A commitment fee of 0.375% initially, subject to a reduction to 0.25% based on achieving a first lien net leverage ratio of 1.00 :1.00, on the unused portion of the Revolving Facility is payable quarterly in arrears. Letter of credit fees are payable on outstanding letters of credit under the Revolving Facility, and fronting fees equal to a percentage to be agreed with each issuing bank (not to exceed 0.125% ) are payable to the issuing banks. The Revolving Facility matures on September 30, 2021 . A maximum first lien net leverage ratio covenant (total debt net of cash on hand to total adjusted EBITDA) of 3.25 :1.00 will apply if we draw upon the Revolving Facility. As of March 31, 2019 , we had availability of $200 million under the Revolving Facility. The Credit Agreement, as amended, provides that, commencing with Versum’s fiscal year ending on September 30, 2017, a percentage of excess cash flow ranging from 0% to 50% , depending on the first lien net leverage ratio, is required to be used to prepay the Term Facility. As of March 31, 2019 , there was no requirement to prepay due to excess cash flows. Senior Notes On September 30, 2016, Versum issued $425 million of 5.5% Senior Notes due 2024 . The Notes are unsecured senior obligations of Versum, guaranteed by each of Versum’s subsidiaries that is a guarantor under the Senior Credit Facilities. The Notes bear interest at a rate of 5.5% per annum payable semiannually on March 15 and September 15 of each year, commencing on March 15, 2017. The Notes will mature on September 30, 2024 . Versum may, at its option, redeem some or all of the Notes during such times and at such prices as described in the Indenture governing the Senior Notes, plus accrued and unpaid interest, if any, to the date of redemption. The agreements governing our indebtedness contain a number of affirmative and negative covenants. We were in compliance with all of our covenants at March 31, 2019 .

Income Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES For fiscal year 2019, Versum’s statutory income tax rate increased in non-U.S. jurisdictions including Taiwan and Korea, which increased Versum’s global effective tax rate by 1.7% . The statutory tax rate in Taiwan increased to 20.0% in fiscal year 2019 from 17.0% in the prior year. Korea had unfavorable changes in their tax laws that effectively increased Versum’s tax rate in Korea by approximately 2.2% . In fiscal 2019, Versum became subject to additional provisions in accordance with the effective dates in the U.S. Tax Act, which was enacted into law on December 22, 2017. The statutory U.S. federal income tax rate is 21.0% for the fiscal year 2019. This is a decrease from fiscal year 2018’s U.S. federal tax rate of 24.5% which represented a blending of the 35.0% statutory rate under prior law and the new 21.0% statutory rate effective January 1, 2018. Additionally, Versum became subject to other new U.S. provisions including the Global Intangible Low Taxed Income (GILTI), Foreign Derived Intangible Income (FDII) deduction, Base Erosion and Anti-Abuse Tax (BEAT) and expanded business interest limitation provisions. The company has elected to treat changes to the GILTI inclusion as a period cost in the period incurred. The income tax effect of all U.S. Tax Act provisions has been considered in the current period tax expense and their net impact on the global effective tax rate for fiscal year 2019 is immaterial. The company will continue to actively monitor and analyze legal developments and new guidance throughout the year and adjust applicable calculations as necessary. Certain other provisions of the U.S. Tax Act, described below, were recorded initially in the quarter ended December 31, 2017 and adjusted during a twelve-month measurement period in accordance with the SEC’s Staff Accounting Bulletin No. 118. The company recorded a final measurement period benefit of $1.7 million during its three-month period ended December 31, 2018, which was the final measurement period available to record provisional adjustments related to the U.S. Tax Act. As of December 31, 2018, the accounting for the income tax effects of the enactment of the U.S. Tax Act have been completed and recorded in the company’s financial statements and no provisional adjustments will be made in subsequent quarters, including the three months ended March 31, 2019 . The measurement period adjustment recorded in the first quarter was a benefit related to federal and state taxes on the mandatory deemed repatriation of certain of the company’s foreign accumulated earnings and reduces the company’s tax on the mandatory deemed repatriation to $52.1 million . The measurement period adjustment is non-recurring and it reduced our U.S. GAAP effective tax rate by 1.1% for the six months ended March 31, 2019 . We expect to elect to pay the federal portion of the resulting liability, net of available tax credits, over the eight-year period provided in the U.S. Tax Act. Versum records U.S. income and foreign withholding taxes on the undistributed earnings of our foreign subsidiaries and corporate joint ventures unless those earnings are indefinitely reinvested. For the six months ended March 31, 2019 , the accrued expense related to withholding taxes on undistributed earnings is $1.4 million .

Financial Instruments

Financial Instruments	6 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments	FINANCIAL INSTRUMENTS We enter into forward exchange contracts to hedge the fair value exposure on inter-company loans. During the three months ended March 31, 2019 and 2018 , this portfolio of forward exchange contracts consisted primarily of Japanese Yen and U.S. Dollars as well as Euros and U.S. Dollars. The maximum remaining term of any forward exchange contract currently outstanding at March 31, 2019 and 2018 was approximately 1 year and 6 months , respectively. At March 31, 2019 and September 30, 2018 , the total notional principal amount of our outstanding hedge contracts was $31.5 million and $36.1 million , respectively. As of March 31, 2019 and September 30, 2018 , there were no derivatives designated as hedging instruments. The tables below summarize the fair values of our derivatives not designated as hedging instruments and balance sheet location of these outstanding derivatives: March 31, 2019 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ — Payables and accrued liabilities $ 0.3 September 30, 2018 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.4 Payables and accrued liabilities $ — Refer to Note 10 , Fair Value , which defines fair value, describes the method for measuring fair value, and provides additional disclosures regarding fair value measurements. The table below summarizes the gain or loss related to our forward contracts: Three Months Ended March 31, Six Months Ended March 31, (In millions) 2019 2018 2019 2018 Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ 0.2 $ 1.9 $ 1.1 $ 1.9 (A) The impact of the non-designated hedges noted above was largely offset by gains and losses resulting from the impact of changes in exchange rates on recognized assets and liabilities denominated in nonfunctional currencies. The cash flows related to all derivative contracts are reported in the operating activities section of the consolidated statements of cash flows.

Fair Value

Fair Value	6 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE Fair value is defined as an exit price, i.e., the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three broad levels as follows: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 - Inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the asset or liability. Level 3 - Inputs that are unobservable for the asset or liability based on our own assumptions (about the assumptions market participants would use in pricing the asset or liability). The methods and assumptions used to measure the fair value of financial instruments are as follows: Derivatives The fair value of our forward exchange contracts is quantified using the income approach and are based on estimates using standard pricing models. These models take into account the value of future cash flows as of the balance sheet date, discounted to a present value using discount factors that match both the time to maturity and currency of the underlying instruments. The computation of the fair values of these instruments is generally performed by the company. These standard pricing models utilize inputs which are derived from or corroborated by observable market data such as interest rate yield curves and currency spot and forward rates. Therefore, the fair value of our derivatives is classified as a level 2 measurement. Refer to Note 9 , Financial Instruments , for a description of derivative instruments, including details on the balance sheet line classifications. Long-term Debt The fair value of our Senior Notes is based primarily on quoted market prices reported on or near the respective balance sheet date and is therefore level 1. The fair value of our Term Facility debt is based on estimates using standard pricing models that take into account the value of future cash flows as of the balance sheet date, discounted to a present value using market based assumptions including published interest rates. This standard valuation model utilizes observable market data. Therefore, the fair value of our debt is classified as a level 2 measurement. The carrying values and fair values of our derivatives and debt are as follows: March 31, 2019 September 30, 2018 Fair Value Carrying Value Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ — $ — $ 0.4 $ 0.4 Liabilities Forward Exchange Contracts $ 0.3 $ 0.3 $ — $ — Long-term Debt Senior Notes $ 446.3 $ 425.0 $ 435.6 $ 425.0 Term Facility 560.6 560.6 567.0 563.5 Total Long-term Debt $ 1,006.9 $ 985.6 $ 1,002.6 $ 988.5 The carrying amounts reported in the consolidated balance sheet for cash and cash items, short-term investments, trade receivables, payables and accrued liabilities, and accrued income taxes approximate fair value due to the short-term nature of these instruments. Accordingly, these items have been excluded from the above table.

Retirement Benefits

Retirement Benefits	6 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Retirement Benefits	RETIREMENT BENEFITS Defined Benefit Pensions Our plans provide certain international employees in Germany, Korea and Taiwan various pension benefits. Charges to expense are based upon actuarial analysis. The components of net periodic pension costs for Versum’s defined benefit pension plans are as follows: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Service cost $ 0.5 $ 0.5 $ 1.0 $ 1.0 Interest cost 0.2 0.2 0.4 0.4 Expected return on assets (0.1 ) — (0.1 ) — Actuarial loss amortization 0.1 — 0.1 — Net periodic pension cost $ 0.7 $ 0.7 $ 1.4 $ 1.4 Defined Contribution Plan Versum provides benefits for all U.S. employees and certain non-U.S. employees under a Versum defined contribution plan. The following table summarizes our defined contribution expense: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Defined contribution expense $ 2.1 $ 2.1 $ 4.3 $ 4.2

Share Based Compensation

Share Based Compensation	6 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	SHARE-BASED COMPENSATION We have the following outstanding share-based compensation awards: (a) stock options; (b) time-based restricted stock units; and (c) market-based restricted stock units. During the six months ended March 31, 2019 , under the Versum Long-Term Incentive Plan we granted annual awards of time-based restricted stock units and market-based restricted stock units, consisting of performance-based restricted stock units. In addition, during the six months ended March 31, 2018 we granted annual awards of market-based restricted stock units, consisting of performance-based restricted stock units and performance-based market stock units. Under all programs, the terms of the awards are fixed at the grant date. Generally we issue new shares upon the payout of restricted stock units and the exercise of stock options. For our Korean employees we pay cash in lieu of issuing shares with respect to restricted stock units. As of March 31, 2019 , there were 4.5 million shares available for future grant under the Versum Long-Term Incentive Plan. Total after-tax share-based compensation awards cost recognized in the consolidated income statement is summarized below: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Before-Tax Share-Based Compensation Award Cost $ 2.6 $ 2.6 $ 5.2 $ 5.0 Income Tax Benefit 0.5 0.6 1.0 1.2 After-Tax Share-Based Compensation Award Cost $ 2.1 $ 2.0 $ 4.2 $ 3.8 Before-tax share-based compensation award cost is primarily included in selling and administrative expense on our consolidated income statements. Total before-tax share-based compensation award cost by type of program was as follows: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Restricted stock units $ 2.4 $ 2.4 $ 4.8 $ 4.7 Director awards 0.2 0.2 0.4 0.3 Before-Tax Share-Based Compensation Cost $ 2.6 $ 2.6 $ 5.2 $ 5.0 Restricted Stock Units New share-based compensation awards During the six months ended March 31, 2019 , under its Long-Term Incentive Plan Versum granted 297,564 time-based restricted stock units and market-based restricted stock units, consisting of performance-based restricted stock units. The time-based restricted stock units were granted at a weighted-average grant-date fair value of $31.83 per unit which vest on September 30, 2021, subject to the holder’s continued employment with the company. The performance-based restricted stock units are earned at the end of a performance period beginning October 1, 2018 and ending September 30, 2021, conditioned on the level of Versum’s total shareholder return in relation to a defined peer group over the three -year performance period. In addition, during the six months ended March 31, 2018 , under its Long-Term Incentive Plan Versum granted 200,088 market-based restricted stock units, consisting of performance-based restricted stock units and performance-based market stock units. The performance-based restricted stock units are earned at the end of a performance period beginning October 1, 2017 and ending September 30, 2020, conditioned on the level of Versum’s total shareholder return in relation to a defined peer group over the three -year performance period. The performance-based market stock units are earned based on the percentage change in the price of Versum’s common stock over the performance period beginning October 1, 2017 and ending September 30, 2020. Subject to the recipient’s continued employment, these market-based restricted stock units granted during the six months ended March 31, 2019 and 2018 generally vest on the date that the Versum Compensation Committee certifies the payout determination under the performance goals, which date must be within 90 days after the end of the performance period. Under GAAP, both the performance-based restricted stock units and performance-based market stock units are considered market-based awards. Vesting for time-based restricted stock units and market based restricted stock units is subject to certain exceptions in the event of involuntary termination by Versum, death, disability or retirement. Upon vesting, restricted stock units represent the right to receive shares of our common stock with the exception of our Korean employees. Our Korean employees are paid in cash based on the fair value of their vested units. Dividend equivalent rights accrue for these awards, but do not vest unless the underlying awards vest. The time-based restricted stock units awarded during the six months ended March 31, 2019 had an estimated grant-date fair value of $31.83 per unit. The market based restricted stock units awarded during the six months ended March 31, 2019 and 2018 had an estimated grant-date fair value of $40.86 and $50.18 , respectively, per unit for the performance-based restricted stock units. The market based restricted stock units awarded during the six months ended March 31, 2018 had an estimated grant-date fair value of $45.71 per unit for the performance-based market stock units. The fair value of market-based restricted stock units was estimated using a Monte Carlo simulation model as these equity awards are tied to a market condition. The model utilizes multiple input variables that determine the probability of satisfying the market condition stipulated in the grant and calculates the fair value of the awards. We generally expense the grant-date fair value of these awards on a straight-line basis over the vesting period; however, expense recognition is accelerated for retirement eligible individuals who meet the requirements for vesting upon retirement. The calculation of the fair value of market-based restricted stock units during the six months ended March 31, 2019 and 2018 used the following assumptions: Six Months Ended March 31, 2019 2018 (In percentages) Expected volatility 29.0 % 28.0 % Risk-free interest rate 2.8 % 1.9 % Expected dividend yield 0.7 % 0.5 % A summary of restricted stock unit activity is presented below: Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average fair value) Outstanding, September 30, 2018 1.1 $ 29.47 Granted 0.3 36.48 Paid out (0.3 ) 24.20 Outstanding, March 31, 2019 1.1 $ 32.63 Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average fair value) Outstanding, September 30, 2017 1.1 $ 25.30 Granted 0.2 47.23 Paid out (0.2 ) 29.68 Outstanding, March 31, 2018 1.1 $ 29.40 Cash payments of $0.2 million for the three and six months ended March 31, 2019 and 2018 were made for restricted stock units paid out of Korea. As of March 31, 2019 and 2018 , there was $18.3 million and $18.9 million , respectively, of unrecognized compensation cost related to restricted stock units. The cost is expected to be recognized over a weighted average period of 2.0 and 2.3 years, respectively. The total fair value of restricted stock units paid out during the three and six months ended March 31, 2019 was $0.5 million and $6.3 million , respectively. The total fair value of restricted stock units paid out during the three and six months ended March 31, 2018 was $0.0 million and $4.8 million , respectively. Stock Options We may grant awards of options to purchase common stock to executive officers and selected employees. All of our outstanding stock options are a result of the conversion in connection with the Separation. The exercise price of stock options equals the market price of our stock on the date of the grant. Options generally vest incrementally over three years and remain exercisable for ten years from the date of grant. During the three and six months ended March 31, 2019 and 2018 , no stock options were granted. A summary of stock option activity is presented below: Shares Weighted Average Exercise Price (In millions, except weighted average exercise price) Outstanding, September 30, 2018 0.5 $ 18.66 Granted — — Exercised (0.1 ) 15.37 Outstanding, March 31, 2019 0.4 $ 19.68 Shares Weighted Average Exercise Price (In millions, except weighted average exercise price) Outstanding, September 30, 2017 0.5 $ 18.55 Granted — — Exercised — — Outstanding, March 31, 2018 0.5 $ 18.61 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, March 31, 2019 4.7 $ 10.7 Exercisable, March 31, 2019 4.7 10.7 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, March 31, 2018 5.2 $ 8.8 Exercisable, March 31, 2018 5.2 8.8 The aggregate intrinsic value represents the amount by which our closing stock price of $50.31 and $37.63 as of March 31, 2019 and 2018 exceeds the exercise price multiplied by the number of in-the-money options outstanding or exercisable. The total intrinsic value of stock options exercised during the three and six months ended March 31, 2019 and 2018 was $3.6 million and $0.3 million , respectively. Compensation cost is generally recognized over the stated vesting period consistent with the terms of the arrangement (i.e., either on a straight-line or graded-vesting basis). Expense recognition is accelerated for retirement-eligible individuals who would meet the requirements for vesting of awards upon their retirement. As of March 31, 2019 , the stock options were fully expensed. Director Awards In November 2018, the Board of Directors increased the annual equity awards under the Versum Long-Term Incentive Plan granted to non-employee directors from a grant date fair value of $100,000 annually to $115,000 annually. In the second quarter 2019 non-employee directors were granted restricted stock units for service on our Board of Directors through the 2020 annual meeting of stockholders. Subject to continued service on the Board of Directors, the restricted stock units vest on the earlier of February 7, 2020, and the date immediately prior to Versum's next annual meeting of stockholders, and will be settled in common stock upon vesting. The grant date fair value per share is equal to the closing sales price of our common stock as reported on the New York Stock Exchange on the date of grant. During the three and six months ended March 31, 2019 , $0.2 million and $0.4 million , respectively, in share-based compensation expense was recognized related to these awards. During the three and six months ended March 31, 2018 , $0.2 million and $0.3 million , respectively, in share-based compensation expense was recognized related to these awards.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS' EQUITY Accumulated Other Comprehensive Income (Loss) The table below summarizes changes in accumulated other comprehensive income (loss) (“AOCL”), net of tax: Net income on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2018 $ — $ (14.8 ) $ (3.4 ) $ (18.2 ) Other comprehensive loss before reclassifications — (6.0 ) — (6.0 ) Amounts reclassified from AOCL — — 0.1 0.1 Net current period other comprehensive income (loss) — (6.0 ) 0.1 (5.9 ) Other comprehensive loss attributable to non-controlling interest — (0.3 ) — (0.3 ) Balance, March 31, 2019 $ — $ (20.5 ) $ (3.3 ) $ (23.8 ) Net income on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 ) Other comprehensive income before reclassifications 0.1 26.3 — 26.4 Amounts reclassified from AOCL — — — — Net current period other comprehensive income 0.1 26.3 — 26.4 Other comprehensive income attributable to non-controlling interest — 1.6 — 1.6 Balance, March 31, 2018 $ (0.1 ) $ 8.7 $ (2.2 ) $ 6.4 The amounts reclassified out of accumulated other comprehensive loss for the six months ended March 31, 2019 and 2018 were $0.1 million and zero , respectively. Cash Dividend On October 31, 2018, the company’s Board of Directors declared a quarterly cash dividend of $0.08 per share, totaling $8.8 million , which was paid on November 27, 2018 to shareholders of record as of November 13, 2018. On January 29, 2019, the company’s Board of Directors declared a quarterly cash dividend of $0.08 per share, totaling $8.8 million , which was paid on February 26, 2019 to shareholders of record as of February 12, 2019. Future dividend declarations, if any, as well as the record and payment dates for such dividends, are subject to the final determination of the company’s Board of Directors.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE The following table sets forth the computation of basic and diluted earnings per share: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 50.4 $ 61.6 $ 111.5 $ 80.3 Denominator Weighted average number of common shares - Basic 109.1 108.9 109.1 108.9 Effect of dilutive securities Employee stock option and other award plans 0.9 0.8 0.8 0.9 Weighted average number of common shares - Diluted 110.0 109.7 109.9 109.8 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 0.46 $ 0.57 $ 1.02 $ 0.74 Net Income Attributable to Versum - Diluted 0.46 0.56 1.01 0.73 For the three and six months ended March 31, 2019 , outstanding share-based awards of 0.0 million and 0.1 million shares were anti-dilutive and therefore excluded from the computation of diluted earnings per share. For the three and six months ended March 31, 2018 , outstanding share-based awards of 0.2 million and 0.1 million shares were anti-dilutive and therefore excluded from the computation of diluted earnings per share.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Litigation Following the public announcement of the merger agreement signed between Versum and Entegris, Inc. (“ Entegris Merger ”), purported stockholders of Versum filed three putative class action lawsuits and one individual lawsuit in the United States District Court for the District of Delaware against Versum and the members of the Versum Board (and, in the case of one of the putative class actions, also against Entegris): Price v. Versum Materials, Inc. et al. , 1:19-cv-00427 (filed on March 1, 2019), Wang v. Versum Materials, Inc. et al. , 1:19-cv-00460 (filed on March 5, 2019), Wheby v. Versum Materials, Inc. et al. , 1:19-cv-00472 (filed on March 6, 2019), and Robert v. Versum Materials, Inc. et al. , 1:19-cv-00511 (filed on March 14, 2019). The lawsuits contain similar allegations contending, among other things, that the registration statement on Form S-4 misstates or fails to disclose certain allegedly material information in violation of federal securities laws. The individual lawsuit ( Wang ) additionally alleges that the members of the Versum Board breached their fiduciary duties in connection with the offer made by Merck KGaA, Darmstadt, Germany (“Merck KGaA”) to purchase all of the issued and outstanding shares of Versum’s common stock at a purchase price of $48.00 per share (the “Initial Merck KGaA Proposal”). Additionally, purported stockholders of Versum filed two putative class action lawsuits in the Court of Chancery of the State of Delaware against Versum, the members of the Versum Board, and Broadridge Corporate Issuer Solutions, Inc.: Plumbers and Steamfitters Local 60 Pension Trust v. Versum Materials, Inc. et al. , 2019-0190-JTL (filed on March 8, 2019) and City of Providence v. Versum Materials, Inc. et al. , 2019-0206-JTL (filed on March 14, 2019). The lawsuits contain similar allegations contending, among other things, that the members of the Versum Board breached their fiduciary duties in connection with the Initial Merck KGaA Proposal and in instituting a shareholder rights agreement (the “Rights Agreement”). One lawsuit ( City of Providence ) additionally contains breach of fiduciary duty allegations arising out of alleged negotiations by members of the Versum Board with Entegris without board authorization and without full disclosure to the board. The lawsuits seek relief declaring that the Rights Agreement is unenforceable or enjoining its use, damages and costs, and other remedies. One lawsuit ( City of Providence ) additionally seeks to enjoin the Entegris Merger. On March 19, 2019, the Delaware Chancery Court entered an order consolidating the two lawsuits under the caption In re Versum Materials, Inc. Stockholder Litigation , Consolidated C.A. No. 2019-0206-JTL. The complaint previously filed by the City of Providence was designated the operative complaint. On March 31, 2019, Plaintiffs in the consolidated lawsuits filed a motion for leave to supplement the complaint. The supplement contains additional breach of fiduciary duty allegations arising out of, among other things, the Board’s consideration of the Initial Merck KGaA Proposal. On April 7, 2019 the Delaware Chancery Court granted Plaintiffs’ motion and on April 8, 2019 Plaintiffs filed their supplement to the operative complaint. Additionally, Plaintiffs and Versum executed a stipulation dated as of March 31, 2019 pursuant to which Plaintiffs agreed to withdraw their motion seeking to enjoin consummation of the Entegris Merger upon termination of the Rights Agreement. On April 3, following Versum’s announcement of the termination of the Rights Agreement, Plaintiffs filed a letter with the court stating that Plaintiffs will no longer seek an injunction and withdrawing their request for expedited proceedings. On April 2, 2019, a purported California class action lawsuit captioned Inocencio Ventura v. Versum Materials, Inc. was filed in the Superior Court of the State of California for the County of Los Angeles, containing various class action allegations under California state wage-and-hour laws, including failure to pay overtime and minimum wages and failure to provide meal and rest breaks, to persons employed in California as hourly-paid, non-exempt employees since April 2015, and other derivative claims, and seeking unspecified monetary damages and attorneys’ fees. Although we cannot predict the ultimate outcome of the litigation described in this Note 15 with certainty, the Company believes that these purported class action lawsuits are without merit and intends to defend against them vigorously. In the normal course of business, Versum may be involved in various other legal proceedings, including commercial, environmental, health, safety, and product liability matters. Although litigation with respect to these matters is routine and incidental to the conduct of our business, such litigation may result in large monetary awards for compensatory and punitive damages. Versum does not currently believe that there are any legal proceedings, individually or in the aggregate, that are reasonably possible to have a material impact on its financial condition, results of operations, or cash flows. While Versum cannot predict the outcome of any litigation, environmental, or regulatory matter or the potential for future litigation or regulatory action, we have evaluated all litigation, environmental and regulatory proceedings, claims and assessments in which Versum is involved, and do not believe that any of these matters, individually or in the aggregate, will result in losses that are materially in excess of amounts accrued or recognized. Refer to Note 21 of "Notes to the Annual Consolidated Financial Statements" in Item 8 of Part II of our Annual Report on Form 10-K for the fiscal year ended September 30, 2018 , for additional information regarding commitments and contingencies.

Segment Information

Segment Information	6 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION 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. Our segments are differentiated by the types of products sold. Segment Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Sales Materials $ 216.5 $ 218.9 $ 438.2 $ 433.5 Delivery Systems and Services 109.1 121.1 226.3 236.4 Corporate 0.6 0.7 1.2 1.6 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5 Operating Income (Loss) Materials $ 65.4 $ 71.7 $ 133.0 $ 137.8 Delivery Systems and Services 34.9 32.9 69.6 66.4 Corporate (3.9 ) (6.8 ) (9.3 ) (15.3 ) Segment Total $ 96.4 $ 97.8 $ 193.3 $ 188.9 Business separation, restructuring and cost reduction actions (13.8 ) (8.2 ) (14.9 ) (10.0 ) Total $ 82.6 $ 89.6 $ 178.4 $ 178.9 March 31, 2019 September 30, 2018 (In millions) Total Assets Materials $ 889.3 $ 862.5 Delivery Systems and Services 175.3 144.9 Corporate 502.6 497.9 Total $ 1,567.2 $ 1,505.3

Proposed Merger Proposed Merger

Proposed Merger Proposed Merger	6 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions Disclosures [Text Block]	17. PROPOSED MERGER On January 28, 2019, the company announced an agreement and plan of merger, dated January 27, 2019, between the company and Entegris, pursuant to which the company would merge with and into Entegris, with Entegris as the surviving corporation. Under the terms of the Entegris merger agreement, which was unanimously approved by the Boards of Directors of both companies, Versum stockholders would receive 1.120 shares of Entegris for each existing share of Versum common stock. Immediately following completion of the merger, Entegris stockholders would own approximately 52.5% and company stockholders would own approximately 47.5% of the issued and outstanding shares of the combined company (based on fully diluted shares outstanding including exercisable options only). The transaction was expected to close in the second half of 2019, subject to the satisfaction of customary closing conditions, including receipt of U.S. and international regulatory approvals and approval by the stockholders of Versum and Entegris. On February 27, 2019, Merck KGaA sent a letter to the Versum board of directors setting forth a non-binding unsolicited proposal to acquire Versum for $48.00 per share in cash. Following discussions between Versum and Merck KGaA, on April 7, 2019, Merck KGaA submitted a revised proposal to the company to acquire the company for $53.00 in cash per share. Later on April 7, 2019, the company notified Entegris that the company’s Board of Directors, in consultation with its legal and financial advisors, had unanimously determined that this revised proposal from Merck KGaA constituted a “Superior Proposal” as defined in the merger agreement with Entegris and that Versum’s Board of Directors intended to consider whether to terminate the merger agreement with Entegris and enter into a definitive merger agreement with Merck KGaA. Consistent with the terms of the merger agreement with Entegris, Entegris had the right, during the four business day period following such notice and ending on April 11, 2019, to propose revisions to the existing merger agreement between Versum and Entegris but declined to do so. On April 12, 2019, the company terminated the merger agreement with Entegris and paid a termination fee of $140 million pursuant thereto to Entegris. Immediately thereafter, Versum and Merck KGaA signed an agreement and plan of merger pursuant to which a wholly owned subsidiary of Merck KGaA would merge with and into Versum, with Versum surviving the merger as a wholly owned subsidiary of Merck KGaA. Upon completion of the merger with Merck KGaA, Versum’s stockholders will have the right to receive $53.00 per share in cash for each share of common stock that they own immediately prior to the completion of the merger. The transaction is expected to close in the second half of 2019, subject to the approval of the company’s stockholders at a special meeting, regulatory clearances and the satisfaction of other customary closing conditions.

Subsequent Event

Subsequent Event	6 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Event	SUBSEQUENT EVENT Cash Dividend On April 30, 2019, the company’s Board of Directors declared a quarterly cash dividend of $0.08 per share, to be paid on May 28, 2019 to all shareholders of record as of May 14, 2019.

Basis of Presentation and Maj_2

Basis of Presentation and Major Accounting Policies (Policies)	6 Months Ended
	Mar. 31, 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 six months ended March 31, 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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	6 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table summarizes revenue from contracts with customers related to the geographic area in which the company operates: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Sales to External Customers United States $ 96.5 $ 102.4 $ 196.6 $ 197.4 Taiwan 59.6 63.3 124.2 122.6 South Korea 111.1 112.7 227.1 231.2 China 19.4 26.8 38.6 47.8 Europe 16.3 15.0 32.0 30.5 Asia, excluding China, Taiwan, and South Korea 23.3 20.5 47.2 42.0 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5 The following table summarizes revenue from contracts with customers disaggregated by product group: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Materials Advanced Materials $ 117.6 $ 119.4 $ 241.2 $ 231.3 Process Materials 98.9 99.5 197.0 202.2 Total Materials 216.5 218.9 438.2 433.5 DS&S Equipment and Installations 92.6 105.1 193.5 205.5 Site Services 16.5 16.0 32.8 30.9 Total DS&S 109.1 121.1 226.3 236.4 Corporate 0.6 0.7 1.2 1.6 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5
Contract with Customer, Asset and Liability	A roll-forward of the company’s contracts in progress, less progress billings is as follows: Six Months Ended March 31, 2019 (In millions) Beginning balance (1) $ 20.3 Change related to revenue in excess of billings 11.7 Ending balance (1) $ 32.0 (1) Beginning and ending balances are current A roll-forward of the company’s deferred revenue is as follows: Six Months Ended March 31, 2019 (In millions) Beginning balance (1) $ 18.7 Amount of deferred revenue recognized in income (44.9 ) Additions to deferred revenue 32.6 Ending balance (1) $ 6.4 (1) Beginning and ending balances are current

Business Separation, Restruct_2

Business Separation, Restructuring, and Cost Reduction Actions (Tables)	6 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Summary of the Carrying Amount of the Accrual for the Business Alignment and Reorganization	The following table summarizes the carrying amount of the accrual for the business separation, restructuring and cost reduction actions at March 31, 2019 : Severance and Other Benefits (In millions) Balance, September 30, 2018 $ 3.2 Current Period Charge (0.3 ) Cash Payments (0.7 ) Balance, March 31, 2019 $ 2.2

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Mar. 31, 2019
Inventory Disclosure [Abstract]
Components of Inventories	The components of inventories are as follows: March 31, 2019 September 30, 2018 (In millions) Inventories at FIFO cost Finished goods $ 116.5 $ 104.3 Work in process 17.3 15.1 Raw materials, supplies and other 69.3 57.7 Inventories $ 203.1 $ 177.1

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Changes to the Carrying Amount of Goodwill by Segment	Changes to the carrying amount of goodwill by segment are as follows: Materials Delivery Systems and Services Total (In millions) Balance, September 30, 2018 $ 165.6 $ 17.4 $ 183.0 Currency translation adjustment (0.4 ) (0.1 ) (0.5 ) Balance, March 31, 2019 $ 165.2 $ 17.3 $ 182.5

Debt (Tables)

Debt (Tables)	6 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Components of Debt	Components of Debt March 31, 2019 September 30, 2018 (In millions) Short-term borrowings (A) $ 0.3 $ — Current portion of long-term debt 5.8 5.8 Long-term debt 972.2 974.2 Total Debt $ 978.3 $ 980.0 (A) Represents borrowing under foreign lines of credit by non-U.S. subsidiaries which are short term in nature. Availability under these lines of credit at March 31, 2019 was $19.9 million .
Long-term Debt	Long-term debt March 31, 2019 September 30, 2018 (In millions) Term loan facility under Credit Agreement $ 560.6 $ 563.5 Revolving facility under Credit Agreement — — 5.5% Senior Notes due 2024 425.0 425.0 Total debt 985.6 988.5 Less debt discount 1.6 1.8 Less deferred debt costs 6.0 6.7 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 972.2 $ 974.2

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the Fair Value and Balance Sheet Location of Outstanding Derivatives	The tables below summarize the fair values of our derivatives not designated as hedging instruments and balance sheet location of these outstanding derivatives: March 31, 2019 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ — Payables and accrued liabilities $ 0.3 September 30, 2018 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.4 Payables and accrued liabilities $ —
Summary of Gain or Loss Related to Forward Contract Cash Flow Hedges and Forward Contracts Not Designated as Hedging Instrument	The table below summarizes the gain or loss related to our forward contracts: Three Months Ended March 31, Six Months Ended March 31, (In millions) 2019 2018 2019 2018 Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ 0.2 $ 1.9 $ 1.1 $ 1.9 (A) The impact of the non-designated hedges noted above was largely offset by gains and losses resulting from the impact of changes in exchange rates on recognized assets and liabilities denominated in nonfunctional currencies.

Fair Value (Tables)

Fair Value (Tables)	6 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Carrying Values and Fair Values of Derivatives and Debt	The carrying values and fair values of our derivatives and debt are as follows: March 31, 2019 September 30, 2018 Fair Value Carrying Value Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ — $ — $ 0.4 $ 0.4 Liabilities Forward Exchange Contracts $ 0.3 $ 0.3 $ — $ — Long-term Debt Senior Notes $ 446.3 $ 425.0 $ 435.6 $ 425.0 Term Facility 560.6 560.6 567.0 563.5 Total Long-term Debt $ 1,006.9 $ 985.6 $ 1,002.6 $ 988.5

Retirement Benefits (Tables)

Retirement Benefits (Tables)	6 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Components of Net Period Pension Costs	The components of net periodic pension costs for Versum’s defined benefit pension plans are as follows: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Service cost $ 0.5 $ 0.5 $ 1.0 $ 1.0 Interest cost 0.2 0.2 0.4 0.4 Expected return on assets (0.1 ) — (0.1 ) — Actuarial loss amortization 0.1 — 0.1 — Net periodic pension cost $ 0.7 $ 0.7 $ 1.4 $ 1.4
Defined Contribution Expense	The following table summarizes our defined contribution expense: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Defined contribution expense $ 2.1 $ 2.1 $ 4.3 $ 4.2

Share-Based Compensation (Table

Share-Based Compensation (Tables)	6 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Cost Recognized	Total after-tax share-based compensation awards cost recognized in the consolidated income statement is summarized below: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Before-Tax Share-Based Compensation Award Cost $ 2.6 $ 2.6 $ 5.2 $ 5.0 Income Tax Benefit 0.5 0.6 1.0 1.2 After-Tax Share-Based Compensation Award Cost $ 2.1 $ 2.0 $ 4.2 $ 3.8
Share-based Compensation Cost by Type of Program	Total before-tax share-based compensation award cost by type of program was as follows: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Restricted stock units $ 2.4 $ 2.4 $ 4.8 $ 4.7 Director awards 0.2 0.2 0.4 0.3 Before-Tax Share-Based Compensation Cost $ 2.6 $ 2.6 $ 5.2 $ 5.0
Assumptions Used in the Calculation of the Fair Value of Market-based Deferred Stock Units	The calculation of the fair value of market-based restricted stock units during the six months ended March 31, 2019 and 2018 used the following assumptions: Six Months Ended March 31, 2019 2018 (In percentages) Expected volatility 29.0 % 28.0 % Risk-free interest rate 2.8 % 1.9 % Expected dividend yield 0.7 % 0.5 %
Summary of Restricted Stock Unit Activity	A summary of restricted stock unit activity is presented below: Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average fair value) Outstanding, September 30, 2018 1.1 $ 29.47 Granted 0.3 36.48 Paid out (0.3 ) 24.20 Outstanding, March 31, 2019 1.1 $ 32.63 Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average fair value) Outstanding, September 30, 2017 1.1 $ 25.30 Granted 0.2 47.23 Paid out (0.2 ) 29.68 Outstanding, March 31, 2018 1.1 $ 29.40
Summary of Stock Option Activity	A summary of stock option activity is presented below: Shares Weighted Average Exercise Price (In millions, except weighted average exercise price) Outstanding, September 30, 2018 0.5 $ 18.66 Granted — — Exercised (0.1 ) 15.37 Outstanding, March 31, 2019 0.4 $ 19.68 Shares Weighted Average Exercise Price (In millions, except weighted average exercise price) Outstanding, September 30, 2017 0.5 $ 18.55 Granted — — Exercised — — Outstanding, March 31, 2018 0.5 $ 18.61 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, March 31, 2019 4.7 $ 10.7 Exercisable, March 31, 2019 4.7 10.7 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, March 31, 2018 5.2 $ 8.8 Exercisable, March 31, 2018 5.2 8.8

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss	The table below summarizes changes in accumulated other comprehensive income (loss) (“AOCL”), net of tax: Net income on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2018 $ — $ (14.8 ) $ (3.4 ) $ (18.2 ) Other comprehensive loss before reclassifications — (6.0 ) — (6.0 ) Amounts reclassified from AOCL — — 0.1 0.1 Net current period other comprehensive income (loss) — (6.0 ) 0.1 (5.9 ) Other comprehensive loss attributable to non-controlling interest — (0.3 ) — (0.3 ) Balance, March 31, 2019 $ — $ (20.5 ) $ (3.3 ) $ (23.8 ) Net income on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 ) Other comprehensive income before reclassifications 0.1 26.3 — 26.4 Amounts reclassified from AOCL — — — — Net current period other comprehensive income 0.1 26.3 — 26.4 Other comprehensive income attributable to non-controlling interest — 1.6 — 1.6 Balance, March 31, 2018 $ (0.1 ) $ 8.7 $ (2.2 ) $ 6.4

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted earnings per share: Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 50.4 $ 61.6 $ 111.5 $ 80.3 Denominator Weighted average number of common shares - Basic 109.1 108.9 109.1 108.9 Effect of dilutive securities Employee stock option and other award plans 0.9 0.8 0.8 0.9 Weighted average number of common shares - Diluted 110.0 109.7 109.9 109.8 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 0.46 $ 0.57 $ 1.02 $ 0.74 Net Income Attributable to Versum - Diluted 0.46 0.56 1.01 0.73

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Reporting	Three Months Ended March 31, Six Months Ended March 31, 2019 2018 2019 2018 (In millions) Sales Materials $ 216.5 $ 218.9 $ 438.2 $ 433.5 Delivery Systems and Services 109.1 121.1 226.3 236.4 Corporate 0.6 0.7 1.2 1.6 Total $ 326.2 $ 340.7 $ 665.7 $ 671.5 Operating Income (Loss) Materials $ 65.4 $ 71.7 $ 133.0 $ 137.8 Delivery Systems and Services 34.9 32.9 69.6 66.4 Corporate (3.9 ) (6.8 ) (9.3 ) (15.3 ) Segment Total $ 96.4 $ 97.8 $ 193.3 $ 188.9 Business separation, restructuring and cost reduction actions (13.8 ) (8.2 ) (14.9 ) (10.0 ) Total $ 82.6 $ 89.6 $ 178.4 $ 178.9
Assets	March 31, 2019 September 30, 2018 (In millions) Total Assets Materials $ 889.3 $ 862.5 Delivery Systems and Services 175.3 144.9 Corporate 502.6 497.9 Total $ 1,567.2 $ 1,505.3

Basis of Presentation and Maj_3

Basis of Presentation and Major Accounting Policies (Details)	6 Months Ended
	Mar. 31, 2019segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of primary operating segments	2

New Accounting Guidance Text (D

New Accounting Guidance Text (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales	$ 189.8	$ 195.8	$ 385.9	$ 387
Selling, General and Administrative Expense	32.6	36.5	68.1	71.8
Operating Income (Loss)	$ 82.6	89.6	$ 178.4	178.9
Restatement Adjustment [Member] | Net Periodic Pension Non Employee Costs Reclassification [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		0.1		0.3
Selling, General and Administrative Expense		0.1		0.1
Operating Income (Loss)		$ 0.2		$ 0.4

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details)	6 Months Ended
	Mar. 31, 2019productsegmentproduct_group
Disaggregation of Revenue [Line Items]
Number of primary operating segments | segment	2
Materials
Disaggregation of Revenue [Line Items]
Number of product groups	2
Delivery Systems and Services
Disaggregation of Revenue [Line Items]
Number of product groups	2
Advanced Materials | Materials
Disaggregation of Revenue [Line Items]
Number of product platforms | product	3

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 326.2	$ 340.7	$ 665.7	$ 671.5
United States
Disaggregation of Revenue [Line Items]
Revenues	96.5	102.4	196.6	197.4
Taiwan
Disaggregation of Revenue [Line Items]
Revenues	59.6	63.3	124.2	122.6
South Korea
Disaggregation of Revenue [Line Items]
Revenues	111.1	112.7	227.1	231.2
China
Disaggregation of Revenue [Line Items]
Revenues	19.4	26.8	38.6	47.8
Europe
Disaggregation of Revenue [Line Items]
Revenues	16.3	15	32	30.5
Asia, excluding China, Taiwan, and South Korea
Disaggregation of Revenue [Line Items]
Revenues	23.3	20.5	47.2	42
Materials | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	216.5	218.9	438.2	433.5
Materials | Operating Segments | Advanced Materials
Disaggregation of Revenue [Line Items]
Revenues	117.6	119.4	241.2	231.3
Materials | Operating Segments | Process Materials
Disaggregation of Revenue [Line Items]
Revenues	98.9	99.5	197	202.2
Delivery Systems and Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	109.1	121.1	226.3	236.4
Delivery Systems and Services | Operating Segments | Equipment and Installations
Disaggregation of Revenue [Line Items]
Revenues	92.6	105.1	193.5	205.5
Delivery Systems and Services | Operating Segments | Site Services
Disaggregation of Revenue [Line Items]
Revenues	16.5	16	32.8	30.9
Corporate | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 0.6	$ 0.7	$ 1.2	$ 1.6

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Change in Contract Assets and Liabilities (Details) $ in Millions	6 Months Ended
	Mar. 31, 2019USD ($)
Change in Contract with Customer, Asset [Abstract]
Beginning balance	$ 20.3
Change related to revenue in excess of billings	11.7
Ending balance	32
Change in Contract with Customer, Liability [Abstract]
Beginning balance	18.7
Amount of deferred revenue recognized in income	(44.9)
Additions to deferred revenue	32.6
Ending balance	$ 6.4

Business Separation, Restruct_3

Business Separation, Restructuring, and Cost Reduction Actions (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Net restructuring charge (gain)	$ (13.8)	$ (8.2)	$ (14.9)	$ (10)

Business Separation, Restruct_4

Business Separation, Restructuring, and Cost Reduction Actions (Details) - Severance and Other Benefits $ in Millions	6 Months Ended
	Mar. 31, 2019USD ($)
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 3.2
Current Period Charge	(0.3)
Cash Payments	(0.7)
Restructuring reserve, ending balance	$ 2.2

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Inventories at FIFO cost
Finished goods	$ 116.5	$ 104.3
Work in process	17.3	15.1
Raw materials, supplies and other	69.3	57.7
Inventories at FIFO cost	$ 203.1	$ 177.1

Goodwill (Details)

Goodwill (Details) $ in Millions	6 Months Ended
	Mar. 31, 2019USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 183
Currency translation adjustment	(0.5)
Goodwill, ending balance	182.5
Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	165.6
Currency translation adjustment	(0.4)
Goodwill, ending balance	165.2
Delivery Systems and Services
Goodwill [Roll Forward]
Goodwill, beginning balance	17.4
Currency translation adjustment	(0.1)
Goodwill, ending balance	$ 17.3

Debt - Components of Debt (Deta

Debt - Components of Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Debt Disclosure [Abstract]
Short-term borrowings	$ 0.3	$ 0
Current portion of long-term debt	5.8	5.8
Long-term debt	972.2	974.2
Total Debt	978.3	$ 980
Foreign lines of credit
Short-term Debt [Line Items]
Availability under line of credit	$ 19.9

Debt - Components of Long Term

Debt - Components of Long Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2016
Debt Instrument [Line Items]
Total debt	$ 985.6	$ 988.5
Less debt discount	1.6	1.8
Less deferred debt costs	6	6.7
Less current portion of long-term debt	5.8	5.8
Long-term debt payable after one year	972.2	974.2
Term loan facility under Credit Agreement
Debt Instrument [Line Items]
Total debt	$ 560.6	563.5
Debt Instrument, Interest Rate, Effective Percentage	4.60%
Line of Credit | Revolving facility under Credit Agreement
Debt Instrument [Line Items]
Total debt	$ 0	0
Senior Notes | 5.5% Senior Notes due 2024
Debt Instrument [Line Items]
Total debt	$ 425	$ 425
Interest rate (as percent)	5.50%		5.50%

Debt (Narrative) (Details)

Debt (Narrative) (Details)	Oct. 10, 2017	Sep. 30, 2016USD ($)	Mar. 31, 2019USD ($)
Term Facility
Debt Instrument [Line Items]
Debt instrument, face amount		$ 575,000,000
Effective interest rate (as percent)			4.60%
Term facility, percent original principal annual amortization (as percent)		1.00%
Term Facility | Minimum
Debt Instrument [Line Items]
Prepayment amount of excess cash flows, percentage			0.00%
Term Facility | Maximum
Debt Instrument [Line Items]
Prepayment amount of excess cash flows, percentage			50.00%
Term Facility | Prior Four Quarter Period After Delivery of Financial Statements
Debt Instrument [Line Items]
Net leverage ratio	2
Term Facility | LIBOR
Debt Instrument [Line Items]
Minimum floor (as percent)		0.75%
Basis spread on variable rate (as percent)	2.00%	2.50%
Term Facility | LIBOR | Leverage Ratio is Met [Member]
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)	1.75%
Term Facility | Base Rate
Debt Instrument [Line Items]
Minimum floor (as percent)		1.75%
Basis spread on variable rate (as percent)	1.00%	1.50%
Term Facility | Base Rate | Leverage Ratio is Met [Member]
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)	0.75%
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 200,000,000
Commitment fee percentage (as percent)		0.375%
Fronting fee percentage (as percent)		0.125%
Maximum net leverage ratio		3.25
Remaining borrowing capacity			$ 200,000,000
Line of Credit | Revolving Credit Facility | Prior Four Quarter Period
Debt Instrument [Line Items]
Net leverage ratio		1
Line of Credit | Revolving Credit Facility | Prior Four Quarter Period After Delivery of Financial Statements
Debt Instrument [Line Items]
Net leverage ratio		1
Line of Credit | Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		2.00%
Basis spread on variable rate, reduction (as percent)		0.25%
Line of Credit | Revolving Credit Facility | LIBOR | Prior Four Quarter Period After Delivery of Financial Statements
Debt Instrument [Line Items]
Basis spread on variable rate, reduction (as percent)		0.25%
Line of Credit | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		1.00%
Senior Notes | 5.5% Senior Notes due 2024
Debt Instrument [Line Items]
Debt instrument, face amount		$ 425,000,000
Interest rate (as percent)		5.50%	5.50%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Income Tax Examination [Line Items]
Foreign Statutory Income Tax Rate Period Increase		1.70%
Foreign Statutory Income Tax Rate				17.00%
Statutory tax rate increase, Korea		2.20%
Statutory tax rate increase, Taiwan		20.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	24.50%
Tax Cuts and Jobs Act 2017 adjustment to the provisional tax accrual	$ 1.7
Expense related to repatriation tax and future repatriation effect on foreign investments		$ 52.1
Tax Cuts and Jobs Act of 2017 increase to effective tax rate		1.10%
Income taxes payable		$ 35.4		$ 43.3
Undistributed foreign earnings, tax		$ 1.4

Financial Instruments (Details)

Financial Instruments (Details) - Derivative Designated as Hedging Instruments $ in Millions	6 Months Ended
	Mar. 31, 2019USD ($)derivative_instrument	Mar. 31, 2018	Sep. 30, 2018USD ($)
Derivative [Line Items]
Number of derivatives | derivative_instrument	0
Cash Flow Hedge | Forward exchange contracts
Derivative [Line Items]
Maximum remaining term	1 year	6 months
Notional amount | $	$ 31.5		$ 36.1

Financial Instruments - Fair Va

Financial Instruments - Fair Value and Balance Sheet Location of Outstanding Derivatives (Details) - Forward exchange contracts - Fair Value - Level 2 - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 0	$ 0.4
Derivative Liability	$ 0.3	$ 0

Financial Instruments - Gain or

Financial Instruments - Gain or Loss Related to Forward Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Forward exchange contracts | Derivatives Not Designated as Hedging Instruments | Other (income) expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Net loss recognized in other (income) expense, net	$ 0.2	$ 1.9	$ 1.1	$ 1.9

Fair Value (Details)

Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	$ 1,006.9	$ 1,002.6
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	985.6	988.5
Level 2 | Fair Value | Term Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	560.6	567
Level 2 | Carrying Value | Term Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	560.6	563.5
Level 2 | Forward Exchange Contracts | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Forward Exchange Contracts	0	0.4
Liabilities, Forward Exchange Contracts	0.3	0
Level 2 | Forward Exchange Contracts | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Forward Exchange Contracts	0	0.4
Liabilities, Forward Exchange Contracts	0.3	0
Level 1 | Fair Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	446.3	435.6
Level 1 | Carrying Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	$ 425	$ 425

Retirement Benefits - Net Perio

Retirement Benefits - Net Periodic Pension Cost (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 0.5	$ 1	$ 1
Interest cost	0.2	0.2	0.4	0.4
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0.1	0	0.1	0
Defined Benefit Plan, Amortization of Gain (Loss)	(0.1)	0	(0.1)	0
Net periodic pension cost	$ 0.7	$ 0.7	$ 1.4	$ 1.4

Retirement Benefits - Defined B

Retirement Benefits - Defined Benefit Contribution (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Defined contribution expense	$ 2.1	$ 2.1	$ 4.3	$ 4.2

Share-Based Compensation (Detai

Share-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0	0	0	0
Closing stock price (in dollars per share)	$ 50.31	$ 37.63	$ 50.31	$ 37.63
Allocated Share-based Compensation Expense	$ 2,600	$ 2,600	$ 5,200	$ 5,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	3,600	300	$ 3,600	$ 300
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)			300,000	200,000
Weighted average grant-date fair value (in dollars per share)			$ 36.48	$ 47.23
Unrecognized compensation cost related to restricted stock units	18,300	18,900	$ 18,300	$ 18,900
Weighted average period to recognize compensation costs			2 years 10 days	2 years 3 months 18 days
Total fair value of shares paid out	500	0	$ 6,300	$ 4,800
Allocated Share-based Compensation Expense	2,400	2,400	$ 4,800	4,700
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Exercise period			10 years
Director Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual Director Award			$ 115,000		$ 100,000
Allocated Share-based Compensation Expense	$ 200	$ 200	$ 400	$ 300
Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)	4,500,000		4,500,000
Long-Term Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)			297,564	200,088
Weighted average grant-date fair value (in dollars per share)			$ 31.83
Long-Term Incentive Plan | Restricted stock units | Vesting period 1, October 1, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage (as percent)		33.33%
Long-Term Incentive Plan | Restricted stock units | Vesting period 2, October 1, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage (as percent)		33.33%
Long-Term Incentive Plan | Restricted stock units | Vesting period 3, October 1, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage (as percent)		33.33%
Long-Term Incentive Plan | Market-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout determination period			90 days
Long-Term Incentive Plan | Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value (in dollars per share)				$ 45.71
Long-Term Incentive Plan | Performance-based market stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value (in dollars per share)			$ 40.86	$ 50.18
Korea [Member] | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation costs paid	$ 0

Share-Based Compensation - Comp

Share-Based Compensation - Compensation Awards Cost Recognized (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Before-Tax Share-Based Compensation Award Cost	$ (2.6)	$ (2.6)	$ (5.2)	$ (5)
Income Tax Benefit	0.5	0.6	1	1.2
After-Tax Share-Based Compensation Award Cost	$ 2.1	$ 2	$ 4.2	$ 3.8

Share-Based Compensation - Befo

Share-Based Compensation - Before-tax Share-Based Compensation Award (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	$ 2.6	$ 2.6	$ 5.2	$ 5
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	2.4	2.4	4.8	4.7
Director Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	$ 0.2	$ 0.2	$ 0.4	$ 0.3

Share-Based Compensation - Assu

Share-Based Compensation - Assumptions used in Calculation of Fair Value of Market-based Restricted Stock Units (Details) - Market-based restricted stock units	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	29.00%	28.00%
Risk-free interest rate	2.80%	1.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.70%	0.50%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted stock units - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 0.5	$ 0	$ 6.3	$ 4.8
Shares
Outstanding, September 30, 2016 (in shares)			1.1	1.1
Paid out (in shares)			0.3	0.2
Forfeited/adjustments (in shares)			(0.3)	(0.2)
Outstanding at June 30, 2017 (in shares)	1.1	1.1	1.1	1.1
Weighted Average Grant-Date Fair Value
Outstanding, September 30, 2016 (in dollars per share)			$ 29.47	$ 25.30
Paid out (in dollars per share)			36.48	47.23
Forfeited/adjustments (in dollars per share)			24.20	29.68
Outstanding at June 30, 2017 (in dollars per share)	$ 32.63	$ 29.40	$ 32.63	$ 29.40

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 3.6	$ 0.3	$ 3.6	$ 0.3
Shares
Outstanding, September 30, 2016 (in shares)			500,000	500,000
Exercised (in shares)	0	0	0	0
Forfeited (in shares)			(100,000)	0
Outstanding at March 31, 2017 (in shares)	400,000	500,000	400,000	500,000
Weighted Average Exercise Price
Outstanding, September 30, 2016 (in dollars per share)			$ 18.66	$ 18.55
Exercised (in dollars per share)			0	0
Forfeited (in dollars per share)			15.37	0
Outstanding at March 31, 2017 (in dollars per share)	$ 19.68	$ 18.61	$ 19.68	$ 18.61
Weighted average remaining contractual terms, options outstanding			4 years 8 months 17 days	5 years 2 months 12 days
Aggregate intrinsic value, options outstanding	$ 10.7		$ 10.7		$ 8.8
Weighted average remaining contractual terms, options exercisable			4 years 8 months 17 days	5 years 2 months 12 days
Aggregate intrinsic value, options exercisable	$ 10.7		$ 10.7		$ 8.8

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			$ 212.4	$ 30.2
Other comprehensive loss before reclassifications			(6)	26.4
Amounts reclassified from AOCL			0.1	0
Total Other Comprehensive Income (Loss)	$ (6.8)	$ 6.6	(5.9)	26.4
Other comprehensive loss attributable to non-controlling interest	(0.3)	0.9	(0.3)	1.6
Stockholders' equity, ending balance	305.9	132.7	305.9	132.7
Accumulated other comprehensive loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			(18.2)	(18.4)
Stockholders' equity, ending balance	(23.8)	6.4	(23.8)	6.4
Net loss on derivatives qualifying as hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			0	(0.2)
Other comprehensive loss before reclassifications			0	0.1
Amounts reclassified from AOCL			0	0
Total Other Comprehensive Income (Loss)			0	0.1
Other comprehensive loss attributable to non-controlling interest			0	0
Stockholders' equity, ending balance	0	(0.1)	0	(0.1)
Foreign currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			(14.8)	(16)
Other comprehensive loss before reclassifications			(6)	26.3
Amounts reclassified from AOCL			0	0
Total Other Comprehensive Income (Loss)			(6)	26.3
Other comprehensive loss attributable to non-controlling interest			(0.3)	1.6
Stockholders' equity, ending balance	(20.5)	8.7	(20.5)	8.7
Pension and postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance			(3.4)	(2.2)
Other comprehensive loss before reclassifications			0	0
Amounts reclassified from AOCL			0.1	0
Total Other Comprehensive Income (Loss)			0.1	0
Other comprehensive loss attributable to non-controlling interest			0	0
Stockholders' equity, ending balance	$ (3.3)	$ (2.2)	$ (3.3)	$ (2.2)

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Postretirement Benefits, net of tax	$ 0.1	$ 0
Pension and Postretirement Benefits, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Postretirement Benefits, net of tax	$ 0.1	$ 0

Stockholders' Equity - Cash Div

Stockholders' Equity - Cash Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 29, 2019	Oct. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Quarterly cash dividend declared (usd per share)	$ 0.08	$ 0.08
Cash dividends paid	$ 8.8	$ 8.8	$ 17.6	$ 10.9
Payments of Dividends			$ 17.6	$ 10.9

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Numerator
Net Income Attributable to Versum	$ 50.4	$ 61.6	$ 111.5	$ 80.3
Denominator
Weighted average number of common shares - Basic (shares)	109.1	108.9	109.1	108.9
Effect of dilutive securities
Employee stock option and other award plans (shares)	0.9	0.8	0.8	0.9
Weighted average number of common shares - Diluted (shares)	110	109.7	109.9	109.8
Earnings Per Common Share Attributable to Versum
Net Income Attributable to Versum - Basic (usd per share)	$ 0.46	$ 0.57	$ 1.02	$ 0.74
Net Income Attributable to Versum - Diluted (usd per share)	$ 0.46	$ 0.56	$ 1.01	$ 0.73
Share-based awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from the computation of earnings per share (shares)	0	0.2	0.1	0.1

Segment Information (Narrative)

Segment Information (Narrative) (Details)	6 Months Ended
	Mar. 31, 2019segment
Segment Reporting [Abstract]
Number of primary operating segments	2

Segment Information - Segments

Segment Information - Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 326.2	$ 340.7	$ 665.7	$ 671.5
Business separation, restructuring and cost reduction actions	(13.8)	(8.2)	(14.9)	(10)
Operating Income (Loss)	82.6	89.6	178.4	178.9
Total Assets	1,567.2		1,567.2		$ 1,505.3
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)	96.4	97.8	193.3	188.9
Operating Segments | Materials
Segment Reporting Information [Line Items]
Revenues	216.5	218.9	438.2	433.5
Operating Income (Loss)	65.4	71.7	133	137.8
Total Assets	889.3		889.3		862.5
Operating Segments | Delivery Systems and Services
Segment Reporting Information [Line Items]
Revenues	109.1	121.1	226.3	236.4
Operating Income (Loss)	34.9	32.9	69.6	66.4
Total Assets	175.3		175.3		144.9
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Revenues	0.6	0.7	1.2	1.6
Operating Income (Loss)	(3.9)	(6.8)	(9.3)	(15.3)
Total Assets	502.6		502.6		$ 497.9
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation, restructuring and cost reduction actions	$ (13.8)	$ (8.2)	$ (14.9)	$ (10)

Proposed Merger (Details)

Proposed Merger (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 11, 2019	Apr. 07, 2019	Feb. 27, 2019	Jan. 28, 2019
Entegris Merger [Member] | Subsequent Event [Member]
Business Combination [Line Items]
End of agreement fee	$ 140
Former Versum Shareholders [Member]
Business Combination [Line Items]
Exchange Ratio				1.120
Shares, percentage owned				47.50%
Per Share			$ 48
Former Entegris Shareholders [Member]
Business Combination [Line Items]
Shares, percentage owned				52.50%
Former Versum Shareholders [Member] | Subsequent Event [Member]
Business Combination [Line Items]
Per Share		$ 53

Subsequent Event (Details)

Subsequent Event (Details) - $ / shares	Apr. 30, 2019	Jan. 29, 2019	Oct. 31, 2018
Subsequent Event [Line Items]
Quarterly cash dividend declared (usd per share)		$ 0.08	$ 0.08
Subsequent event
Subsequent Event [Line Items]
Quarterly cash dividend declared (usd per share)	$ 0.08

Subsequent Event Business Combi

Subsequent Event Business Combination (Details)	Jan. 28, 2019shares
Entegris Merger [Domain]
Business Combination [Line Items]
Shares, percentage owned	52.50%
Former Versum Shareholders [Member]
Business Combination [Line Items]
Exchange Ratio	1.120
Shares, percentage owned	47.50%