Versum Materials (VSM) 10-Q 8 Feb 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2017	Jan. 26, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Versum Materials, Inc.
Entity Central Index Key	1,660,690
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		108,934,561

CONSOLIDATED INCOME STATEMENTS

CONSOLIDATED INCOME STATEMENTS (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Sales	$ 330.8	$ 270.8
Cost of sales	191.6	150.9
Selling and administrative	35.3	30.2
Research and development	12.7	10.3
Business separation, restructuring and cost reduction actions	1.8	3.2
Other (income) expense, net	0.5	(2.9)
Operating Income (Loss)	88.9	79.1
Interest expense	11.3	11.5
Gain (Loss) on Extinguishment of Debt	2.1	0
Income Before Taxes	75.5	67.6
Income tax provision	54.9	15.3
Net Income	20.6	52.3
Less: Net Income Attributable to Non-Controlling Interests	2	1.5
Net Income Attributable to Versum	$ 18.6	$ 50.8
Net income attributable to Versum per common share:
Basic (usd per share)	$ 0.17	$ 0.47
Diluted (usd per share)	$ 0.17	$ 0.47
Shares used in computing per common share amounts:
Basic (shares)	108.9	108.7
Diluted (shares)	109.7	109.2

CONSOLIDATED COMPREHENSIVE INCO

CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 20.6	$ 52.3
Other Comprehensive Income (Loss), net of tax
Translation adjustments, net	19.7	(30.1)
Gain from hedging activities	0.1	0
Pension activity, net of tax of $0 and $1.5, respectively	0	(5.5)
Total Other Comprehensive Income (Loss)	19.8	(35.6)
Comprehensive Income	40.4	16.7
Net Income Attributable to Non-controlling Interests	2	1.5
Other Comprehensive Income (Loss) Attributable to Non-controlling Interests	0.7	(1)
Comprehensive Income Attributable to Versum	$ 37.7	$ 16.2

CONSOLIDATED COMPREHENSIVE INC4

CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS (Unaudited) (Parentheticals) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Pension activity, tax	$ 0	$ 1.5

CONSOLIDATED BALANCE SHEETS (Un

CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Current Assets
Cash and cash items	$ 278.3	$ 271.4
Trade receivables, net	157.7	145.3
Inventories	165.3	151.6
Contracts in progress, less progress billings	24.5	15.6
Prepaid expenses	17.4	12.2
Other current assets	9.1	10.8
Total Current Assets	652.3	606.9
Plant and equipment:
Plant and equipment, at cost	998	955.2
Less: accumulated depreciation	641.1	624.9
Plant and equipment, net	356.9	330.3
Goodwill	185.7	182.6
Intangible assets, net	68.9	70.8
Other noncurrent assets	58.3	56.2
Total Noncurrent Assets	669.8	639.9
Total Assets	1,322.1	1,246.8
Current Liabilities
Payables and accrued liabilities	100.5	120.8
Accrued income taxes	51.7	31.4
Current portion of long-term debt	5.8	5.8
Total Current Liabilities	158	158
Long-term debt	977.1	977
Noncurrent income tax payable	43.4	0
Deferred tax liabilities	30	37.3
Other noncurrent liabilities	53.9	49.9
Total Noncurrent Liabilities	1,104.4	1,064.2
Total Liabilities	1,262.4	1,222.2
Commitments and Contingencies - See Note 14
Stockholders’ Equity (Deficit)
Common stock (par value $1 per share; 250,000,000 shares authorized; outstanding 108,928,208 and 108,736,979 at December 31, 2017 and September 30, 2017, respectively)	108.9	108.8
Capital in excess of par	0	4.8
Accumulated deficit	(87.2)	(105.2)
Accumulated other comprehensive income (loss)	0.7	(18.4)
Total Versum’s Stockholders’ Equity (Deficit)	22.4	(10)
Non-controlling Interests	37.3	34.6
Total Stockholders’ Equity	59.7	24.6
Total Liabilities and Stockholders’ Equity	$ 1,322.1	$ 1,246.8

CONSOLIDATED BALANCE SHEETS (U6

CONSOLIDATED BALANCE SHEETS (Unaudited) (Parentheticals) - $ / shares	Dec. 31, 2017	Sep. 30, 2017
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)	108,928,208	108,736,979

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income	$ 20.6	$ 52.3
Less: Net Income Attributable to Non-Controlling Interests	2	1.5
Net Income Attributable to Versum	18.6	50.8
Adjustments to reconcile income to cash provided by operating activities:
Depreciation and amortization	11.6	10.9
Deferred income taxes	(7.5)	1.7
Gain on sale of assets	(0.3)	(0.2)
Share-based compensation	2.4	1.6
Other adjustments	(4.9)	(1.1)
Working capital changes that provided (used) cash:
Trade receivables	(10.1)	(8.6)
Inventories	(9.7)	(1.3)
Contracts in progress, less progress billings	(7.6)	2.4
Payables and accrued liabilities	(22.4)	19.2
Accrued income taxes	60.2	10.2
Other working capital	8.8	4.2
Cash Provided by Operating Activities	39.1	89.8
Investing Activities
Additions to plant and equipment	(28.7)	(9.6)
Proceeds from sale of assets and investments	0.4	0.8
Cash Used for Investing Activities	(28.3)	(8.8)
Financing Activities
Payments on long-term debt	(1.4)	(1.4)
Debt issuance costs	0	(1.7)
Dividends paid to shareholders	(5.5)	0
Other financing activity	(1.6)	0.1
Cash Used for Financing Activities	(8.5)	(3)
Effect of Exchange Rate Changes on Cash	4.6	(4.9)
Increase in Cash and Cash Items	6.9	73.1
Cash and Cash items-Beginning of Year	271.4
Cash and Cash items-End of Period	278.3	178.7
Interest Paid	4.9	4.9
Income Taxes Paid	$ 2.3	$ 2.4

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par	Accumulated Deficit	Air Products’ Net Investment	Accumulated Other Comprehensive Income (Loss)	Total Versum’s Stockholders’ Equity (Deficit)	Non-controlling Interests
Stockholders' equity, beginning balance at Sep. 30, 2016	$ (103.4)	$ 0	$ 0	$ 0	$ (127.3)	$ (10)	$ (137.3)	$ 33.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	52.3				50.8		50.8	1.5
Net Transfer to Air Products	(158.5)			(292.1)	135.4	(1.8)	(158.5)	0
Reclassification of Air Products' net investment to additional paid in capital			8.1		(8.1)
Issuance of common stock at separation	108.7	108.7					108.7
Other comprehensive income	(33.8)					(32.8)	(32.8)	(1)
Share-based compensation	0.5		0.5		0		0.5
Stockholders' equity, ending balance at Dec. 31, 2016	(134.2)	108.7	8.6	(241.3)	0	(44.6)	(168.6)	34.4
Stockholders' equity, beginning balance at Sep. 30, 2017	24.6	108.8	4.8	(105.2)	0	(18.4)	(10)	34.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20.6			18.6			18.6	2
Cash dividend paid	(5.5)		(4.9)	(0.6)			(5.5)
Issuance of common stock through shared based compensation plans	0.1	0.1					0.1
Other comprehensive income	19.8					19.1	19.1	0.7
Share-based compensation	0.1		0.1				0.1
Stockholders' equity, ending balance at Dec. 31, 2017	$ 59.7	$ 108.9	$ 0	$ (87.2)	$ 0	$ 0.7	$ 22.4	$ 37.3

Basis of Presentation and Major

Basis of Presentation and Major Accounting Policies	3 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Major Accounting Policies	BASIS OF PRESENTATION AND MAJOR ACCOUNTING POLICIES In September 2016, Versum Materials, Inc. was formed and after its Separation from Air Products on October 1, 2016, Versum began operating as an independent public company with its common stock listed under the symbol “VSM” on the New York Stock Exchange. We are a global business that provides innovative solutions for specific customer applications within niche markets based upon expertise in specialty materials. Our business employs applications technology to provide solutions to the semiconductor industry through chemical synthesis, analytical technology, process engineering, and surface science. We are comprised of two operating segments, Materials and Delivery Systems and Services, under which we manage our operations and assess performance, and a Corporate segment. 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, 2017 . 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 months ended December 31, 2017 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, 2017 . There have been no significant changes to these accounting policies during the three months ended December 31, 2017 . 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	3 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
New Accounting Guidance	NEW ACCOUNTING GUIDANCE Accounting Guidance Implemented Goodwill Impairment In January 2017, the Financial Accounting Standards Board (“FASB”) issued guidance simplifying the test for goodwill impairment, which removes certain steps from the goodwill impairment test. The guidance is effective for annual periods beginning after December 15, 2019, including interim periods within those periods, with early adoption permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company adopted the standard effective October 1, 2017. The adoption did not have a material impact on the Consolidated Financial Statements. Measurement of Inventory In July 2015, the FASB issued guidance to simplify the measurement of inventory recorded using either the first-in, first-out (“FIFO”) or average cost basis by changing the subsequent measurement guidance from lower of cost or market to the lower of cost or net realizable value. Inventory measured using last-in, first-out (“LIFO”) is not impacted. The Company adopted the standard effective October 1, 2017. This guidance did not have a significant impact on our Consolidated Financial Statements. New Accounting Guidance to be Implemented 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 10 , Retirement Benefits . The Company is currently evaluating the impact of adopting this guidance. Derecognition of Non-financial Assets In February 2017, the FASB issued guidance which clarifies the scope of the derecognition of nonfinancial assets, the definition of in-substance financial assets, and impacts the accounting for partial sales of nonfinancial assets by requiring full gain recognition upon the sale. The guidance is effective for reporting periods beginning after December 15, 2017 and permits the use of either retrospective or modified retrospective methods of adoption. In addition, an entity is required to apply the amendments in this update at the same time that it applies the amendments in the revenue recognition standard. The Company will adopt the standard effective October 1, 2018. The adoption is not expected to have 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 will adopt the standard effective October 1, 2018. The adoption is not expected to 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 guidance can be adopted either retrospectively or as a cumulative-effect adjustment as of the date of adoption. The Company will adopt the standard effective October 1, 2018. The standard could impact the amount and timing of revenue that we recognize. We are currently evaluating the adoption alternatives and impact that this standard and respective updates will have on our Consolidated Financial Statements. Leases In February 2016, 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 must 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. We are currently evaluating the impact of adopting this new guidance 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. We are currently evaluating the impact of adopting this new guidance on our Consolidated Financial Statements.

Business Separation, Restructur

Business Separation, Restructuring, and Cost Reduction Actions	3 Months Ended
	Dec. 31, 2017
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 months ended December 31, 2017 , we recognized a net charge of $1.8 million . The net charge primarily consisted of additional costs as a result of the relocation of certain research and development activities and headquarters and set up of the stand-alone organization and infrastructure. During the three months ended December 31, 2016 , we recognized a net charge of $3.2 million . The net charge primarily consisted of additional costs as a result of the relocation of certain research and development activities and headquarters and set up of the stand-alone organization and infrastructure. The following table summarizes the carrying amount of the accrual for the business realignment and reorganization at December 31, 2017 : Severance and Other Benefits Total (In millions) Balance, September 30, 2017 $ 4.2 $ 4.2 Current Period Charge 0.2 0.2 Cash Payments (1.1 ) (1.1 ) Balance, December 31, 2017 $ 3.3 $ 3.3

Inventories

Inventories	3 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	INVENTORIES The components of inventories are as follows: December 31, 2017 September 30, 2017 (In millions) Inventories at FIFO cost Finished goods $ 95.1 $ 87.6 Work in process 23.2 20.3 Raw materials, supplies and other 56.0 52.5 174.3 160.4 Less: Excess of FIFO cost over LIFO cost (9.0 ) (8.8 ) Inventories $ 165.3 $ 151.6 FIFO cost approximates replacement cost.

Goodwill

Goodwill	3 Months Ended
	Dec. 31, 2017
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, 2017 $ 165.3 $ 17.3 $ 182.6 Currency translation adjustment 2.7 0.4 3.1 Balance, December 31, 2017 $ 168.0 $ 17.7 $ 185.7 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 December 31, 2017 .

Debt

Debt	3 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	DEBT Components of Debt December 31, 2017 September 30, 2017 (In millions) Short-term borrowings (A) $ — $ — Current portion of long-term debt 5.8 5.8 Long-term debt 977.1 977.0 Total Debt $ 982.9 $ 982.8 (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 December 31, 2017 is $20.7 million . Long-term debt December 31, 2017 September 30, 2017 (In millions) Term loan facility under Credit Agreement $ 567.8 $ 569.3 Revolving facility under Credit Agreement — — 5.500% Senior Notes due 2024 425.0 425.0 Total debt 992.8 994.3 Less debt discount 2.1 2.5 Less deferred debt costs 7.8 9.0 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 977.1 $ 977.0 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 3.69% as of December 31, 2017 ). 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% , and after delivery of the financial statements for the first full fiscal quarter, subject to a 0.25% margin reduction based on achieving a first lien net leverage ratio of 1.00 :1.00 for the prior four-quarter period. 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 for the prior four-quarter period after delivery of the financial statements for the first full fiscal quarter, 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 December 31, 2017 , 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 December 31, 2017 , 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 December 31, 2017 .

Income Taxes

Income Taxes	3 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was enacted in the U.S. Certain provisions of the Tax Act are effective for the Company’s fiscal year 2018, whereas other provisions of the Tax Act will not apply to the Company until the Company’s fiscal year 2019. For fiscal year 2018, Versum’s statutory U.S. federal income tax rate is expected to be 24.5% , which represents a blending of the 35.0% statutory rate under prior law and the new 21.0% statutory rate effective January 1, 2018, prorated based on the number of days during the Company’s current fiscal year that each rate was effective. For fiscal years 2019 and later, the Company’s statutory U.S. federal income tax rate will be 21.0% . As a result of the Tax Act, during the quarter the Company recorded a provisional net one-time charge of $37.6 million . This charge is comprised of a $49.0 million charge for federal and state taxes on the mandatory deemed repatriation of certain of the Company’s foreign accumulated earnings. We expect to elect to pay the federal portion of the resulting liability over the eight year period provided in the Tax Act, with $3.8 million of the federal liability payable in connection with our fiscal year 2018. The deemed repatriation charge was partially offset by an $11.4 million tax benefit related to the estimated revaluation of the Company’s deferred tax assets and liabilities using the U.S. statutory federal and state income tax rates that are anticipated to apply when the deferred tax assets and liabilities will become current and the impact of compensation related charges under the Tax Act on deferred taxes. The methodology used in calculating these provisional items incorporates assumptions about required tax adjustments to book earnings, foreign taxes paid, future executive compensation levels, estimated temporary book to tax differences, pending guidance and other items. We will continue to obtain information, actively monitor developments, complete our tax compliance cycles, analyze and review the available information, and expect to adjust the provisional tax accrual consistent with the SEC’s Staff Accounting Bulletin No. 118. Beginning in the Company’s fiscal year 2019, Versum’s U.S. interest expense deductions will be limited to 30.0% of the Company’s U.S. adjusted taxable income, as defined in the Tax Act. Any deduction limited by this provision could be carried forward. In addition, certain international and executive compensation provisions in the Tax Act will not apply to us until our fiscal year 2019. 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. As a result, foreign withholding tax cost of $1.2 million was recognized.

Financial Instruments

Financial Instruments	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 , this portfolio of forward exchange contracts consisted primarily of Japanese Yen and U.S. Dollars as well as Euros and U.S. Dollars. During the three months ended December 31, 2016 , this portfolio of forward exchange contracts consisted primarily of Korean Won and U.S. Dollars as well as Euros and U.S. Dollars. The maximum remaining term of any forward exchange contract currently outstanding at December 31, 2017 and 2016 was approximately 9 months. At December 31, 2017 and September 30, 2017 , the total notional principal amount of our outstanding hedge contracts was $32.1 million and $158.4 million , respectively. As of December 31, 2017 and September 30, 2017 , 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: December 31, 2017 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.3 Payables and accrued liabilities $ 0.1 September 30, 2017 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.9 Payables and accrued liabilities $ 1.5 Refer to Note 9 , 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: (In millions) Three Months Ended December 31, 2017 Three Months Ended December 31, 2016 Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ — $ 0.2 (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	3 Months Ended
	Dec. 31, 2017
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 8 , 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: December 31, 2017 September 30, 2017 Fair Value Carrying Value Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ 0.3 $ 0.3 $ 0.9 $ 0.9 Liabilities Forward Exchange Contracts $ 0.1 $ 0.1 $ 1.5 $ 1.5 Long-term Debt Senior Notes $ 456.9 $ 425.0 $ 450.5 $ 425.0 Term Facility 571.7 567.8 575.7 569.3 Total Long-term Debt $ 1,028.6 $ 992.8 $ 1,026.2 $ 994.3 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	3 Months Ended
	Dec. 31, 2017
Compensation and Retirement Disclosure [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 December 31, 2017 2016 (In millions) Service cost $ 0.5 $ 0.6 Interest cost 0.2 0.1 Actuarial loss amortization — 0.1 Net periodic pension cost $ 0.7 $ 0.8 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 December 31, 2017 2016 (In millions) Defined contribution expense $ 2.1 $ 1.9

Share Based Compensation

Share Based Compensation	3 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	SHARE-BASED COMPENSATION In accordance with the Employee Matters Agreement entered into between Versum and Air Products on September 29, 2016 in connection with the Separation, all share-based compensation awards previously granted to Versum employees under Air Products’ Long-Term Incentive Plan that were outstanding on October 1, 2016, other than restricted stock, were adjusted and converted into Versum equity with substantially the same terms and conditions as the original Air Products awards. To preserve the aggregate intrinsic value of these share-based compensation awards, as measured immediately before and immediately after the Separation. The converted awards will continue to vest over the original vesting period defined at the grant date. Versum was allocated share-based compensation expense associated with its employees based on these adjusted and converted share-based compensation awards. As a result of the conversion, 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 three months ended December 31, 2016, under the Versum Long-Term Incentive Plan we made a one-time Founders grant of time-based restricted stock units. In addition, during the three months ended December 31, 2017 and 2016 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. We issue new shares upon the payout of restricted stock units and the exercise of stock options. As of December 31, 2017 , there were 3.2 million shares available for future grant under the Versum Long-Term Incentive Plan. Share-based compensation awards cost recognized in the consolidated income statement is summarized below: Three Months Ended December 31, 2017 2016 (In millions) Before-Tax Share-Based Compensation Award Cost $ 2.4 $ 1.6 Income Tax Benefit 0.6 0.5 After-Tax Share-Based Compensation Award Cost $ 1.8 $ 1.1 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 December 31, 2017 2016 (In millions) Restricted stock units $ 2.3 $ 1.5 Stock options — 0.1 Director awards 0.1 — Before-Tax Share-Based Compensation Cost $ 2.4 $ 1.6 Restricted Stock Units Converted share-based compensation awards . As a result of the conversion in connection with the Separation described above, Versum executive officers and employees have outstanding time-based restricted stock units and market-based restricted stock units. These converted restricted stock units entitle the recipient to shares of common stock and accumulated dividends upon vesting. The payout of the converted market-based restricted stock units is conditioned on continued employment during a three year deferral period subject to payout upon death, disability, or retirement. The earn-out amount of these awards is based on a formula to be determined by the Versum Compensation Committee. The converted time-based restricted stock units vest four years after the grant date subject to payout upon death, disability or retirement. Upon involuntary termination without cause, a pro rata portion of restricted stock units will vest. Dividend equivalents are paid in cash and equal the dividends that would have accrued on a share of stock from the grant date to the vesting date. New share-based compensation awards During the three months ended December 31, 2017 , 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. During the three months ended December 31, 2016, under the Versum Long-Term Incentive Plan we made a one-time Founders grant of 424,247 time-based restricted stock units at a weighted-average grant-date fair value of $22.53 per unit. One third of the Founders RSUs vest on October 1, 2018, one third vest on October 1, 2019, and one third vest on October 1, 2020, subject to the holder’s continued employment with the Company. In addition, during the three months ended December 31, 2016 , under its Long-Term Incentive Plan Versum granted 304,520 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, 2016 and ending September 30, 2019, 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, 2016 and ending September 30, 2019. Subject to the recipient’s continued employment, these restricted stock units granted in 2017 and 2016 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. Vesting is subject to certain exceptions in the event of involuntary termination by Versum, death, disability or retirement. Under GAAP, both the performance-based restricted stock units and performance-based market stock units are considered market-based awards. Upon vesting, restricted stock units represent the right to receive shares of our common stock. Dividend equivalent rights accrue for these awards, but do not vest unless the underlying awards vest. The market-based restricted stock units awarded during the three months ended December 31, 2017 and 2016 had an estimated grant-date fair value of $50.18 and $29.68 , respectively, per unit for the performance-based restricted stock units and $45.71 and $28.37 , respectively, 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 three months ended December 31, 2017 and 2016 used the following assumptions: Three Months Ended December 31, 2017 2016 (In percentages) Expected volatility 28.0 % 28.7 % Risk-free interest rate 1.9 % 1.4 % Expected dividend yield 0.5 % — % A summary of restricted stock unit activity is presented below: Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average) Outstanding, September 30, 2017 1.1 $ 25.30 Granted 0.2 48.39 Paid out (0.2 ) 29.68 Outstanding, December 31, 2017 1.1 $ 29.31 Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average) Outstanding, September 30, 2016 — $ — Converted on October 1, 2016 0.5 22.85 Granted 0.7 25.30 Paid out (0.1 ) 15.55 Outstanding, December 31, 2016 1.1 $ 25.18 No cash payments were made for restricted stock units for the three months ended December 31, 2017 and 2016 . As of December 31, 2017 and 2016 , there was $21.2 million and $21.0 million , respectively, of unrecognized compensation cost related to restricted stock units. The cost is expected to be recognized over a weighted average period of 2.6 and 3.2 years, respectively. The total fair value of restricted stock units paid out during the three months ended December 31, 2017 and 2016 , including shares vested in prior periods, was $5.0 million and $1.5 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 as described above. 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 months ended December 31, 2017 and 2016 , no stock options were granted. A summary of stock option activity is presented below: Shares Weighted Average Exercise Price (In millions, except weighted average) Outstanding, September 30, 2017 0.5 $ 18.55 Granted — — Exercised — — Outstanding, December 31, 2017 0.5 $ 18.56 Shares Weighted Average Exercise Price (In millions, except weighted average) Outstanding, September 30, 2016 — $ — Converted on October 1, 2016 0.5 18.37 Granted — — Exercised — — Outstanding, December 31, 2016 0.5 $ 18.36 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, December 31, 2017 5.4 $ 9.1 Exercisable, December 31, 2017 5.4 9.1 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, December 31, 2016 6.1 $ 5.1 Exercisable, December 31, 2016 6.0 5.1 The aggregate intrinsic value represents the amount by which our closing stock price of $37.85 and $28.07 as of December 31, 2017 and 2016 exceeds the exercise price multiplied by the number of in-the-money options outstanding or exercisable. The total intrinsic value of stock options exercised was zero during the three months ended December 31, 2017 and 2016 . 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 December 31, 2017 and 2016 , there was $0.0 million and $0.1 million , respectively, of unrecognized compensation cost related to non-vested stock options, which is expected to be recognized over a weighted average period of zero and 0.9 years, respectively. Director Awards Non-employee directors are granted equity awards under the Versum Long-Term Incentive Plan, with a grant date fair value of $100,000 annually. 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 months ended December 31, 2017 and 2016 , $0.1 million and $0.0 million , respectively, in share-based compensation expense was recognized related to these awards.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS' EQUITY Accumulated Other Comprehensive Income (Loss) The table below summarizes changes in accumulated other comprehensive 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, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 ) Other comprehensive income before reclassifications 0.1 19.7 — 19.8 Net transfers from Air Products — — — — Amounts reclassified from AOCL — — — — Net current period other comprehensive income 0.1 19.7 — 19.8 Other comprehensive income attributable to non-controlling interest — 0.7 — 0.7 Balance, December 31, 2017 $ (0.1 ) $ 3.0 $ (2.2 ) $ 0.7 Net loss on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2016 $ (0.2 ) $ (9.8 ) $ — $ (10.0 ) Other comprehensive loss before reclassifications (3.4 ) (33.9 ) — (37.3 ) Net transfers from Air Products — 3.8 (5.6 ) (1.8 ) Amounts reclassified from AOCL 3.4 — 0.1 3.5 Net current period other comprehensive loss — (30.1 ) (5.5 ) (35.6 ) Other comprehensive loss attributable to non-controlling interest — (1.0 ) — (1.0 ) Balance, December 31, 2016 $ (0.2 ) $ (38.9 ) $ (5.5 ) $ (44.6 ) The table below summarizes the reclassifications out of accumulated other comprehensive loss and the affected line item on the consolidated income statements: Three Months Ended December 31, 2017 2016 (In millions) Pension and Postretirement Benefits, net of tax (A) $ — $ 0.1 (A) The components include actuarial loss amortization and are reflected in net periodic benefit cost. Refer to Note 10 , Retirement Benefits , for further information. Cash Dividend Holders of the Company’s common stock are entitled to receive dividends when they are declared by the Company’s Board of Directors. On October 31, 2017, the Company’s Board of Directors declared a quarterly cash dividend of $0.05 per share, totaling $5.5 million , which was paid on November 27, 2017 to shareholders of record as of November 13, 2017. 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	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 2016 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 18.6 $ 50.8 Denominator Weighted average number of common shares - Basic 108.9 108.7 Effect of dilutive securities Employee stock option and other award plans 0.8 0.5 Weighted average number of common shares - Diluted 109.7 109.2 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 0.17 $ 0.47 Net Income Attributable to Versum - Diluted 0.17 0.47 For the three months ended December 31, 2017 and 2016 , outstanding share-based awards of 0.1 million and 0.2 million shares, respectively, were anti-dilutive and therefore excluded from the computation of diluted earnings per share.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Litigation In the normal course of business, Versum may be involved in various 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 already recognized, if any. 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, 2017 , for additional information regarding commitments and contingencies.

Segment Information

Segment Information	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 2016 (In millions) Sales Materials $ 214.6 $ 208.0 Delivery Systems and Services 115.3 61.9 Corporate 0.9 0.9 Total $ 330.8 $ 270.8 Operating Income (Loss) Materials $ 65.8 $ 72.9 Delivery Systems and Services 33.4 12.4 Corporate (8.5 ) (3.0 ) Segment Total $ 90.7 $ 82.3 Business separation, restructuring and cost reduction actions (1.8 ) (3.2 ) Total $ 88.9 $ 79.1 December 31, 2017 September 30, 2017 (In millions) Total Assets Materials $ 805.5 $ 773.8 Delivery Systems and Services 135.7 110.9 Corporate 380.9 362.1 Total $ 1,322.1 $ 1,246.8

Subsequent Event

Subsequent Event	3 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Event	SUBSEQUENT EVENT Cash Dividend On January 29, 2018, the Company’s Board of Directors declared a quarterly cash dividend of $0.05 per share, to be paid on February 27, 2018 to shareholders of record as of February 13, 2018.

Basis of Presentation and Maj25

Basis of Presentation and Major Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2017
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, 2017 . 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.
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.

Business Separation, Restruct26

Business Separation, Restructuring, and Cost Reduction Actions (Tables)	3 Months Ended
	Dec. 31, 2017
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 realignment and reorganization at December 31, 2017 : Severance and Other Benefits Total (In millions) Balance, September 30, 2017 $ 4.2 $ 4.2 Current Period Charge 0.2 0.2 Cash Payments (1.1 ) (1.1 ) Balance, December 31, 2017 $ 3.3 $ 3.3

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Components of Inventories	The components of inventories are as follows: December 31, 2017 September 30, 2017 (In millions) Inventories at FIFO cost Finished goods $ 95.1 $ 87.6 Work in process 23.2 20.3 Raw materials, supplies and other 56.0 52.5 174.3 160.4 Less: Excess of FIFO cost over LIFO cost (9.0 ) (8.8 ) Inventories $ 165.3 $ 151.6

Goodwill (Tables)

Goodwill (Tables)	3 Months Ended
	Dec. 31, 2017
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, 2017 $ 165.3 $ 17.3 $ 182.6 Currency translation adjustment 2.7 0.4 3.1 Balance, December 31, 2017 $ 168.0 $ 17.7 $ 185.7

Debt (Tables)

Debt (Tables)	3 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Components of Debt	Components of Debt December 31, 2017 September 30, 2017 (In millions) Short-term borrowings (A) $ — $ — Current portion of long-term debt 5.8 5.8 Long-term debt 977.1 977.0 Total Debt $ 982.9 $ 982.8 (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 December 31, 2017 is $20.7 million .
Long-term Debt	Long-term debt December 31, 2017 September 30, 2017 (In millions) Term loan facility under Credit Agreement $ 567.8 $ 569.3 Revolving facility under Credit Agreement — — 5.500% Senior Notes due 2024 425.0 425.0 Total debt 992.8 994.3 Less debt discount 2.1 2.5 Less deferred debt costs 7.8 9.0 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 977.1 $ 977.0

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Dec. 31, 2017
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: December 31, 2017 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.3 Payables and accrued liabilities $ 0.1 September 30, 2017 Balance Sheet Location Amount Balance Sheet Location Amount (In millions) Forward exchange contracts Other current assets $ 0.9 Payables and accrued liabilities $ 1.5
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: (In millions) Three Months Ended December 31, 2017 Three Months Ended December 31, 2016 Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ — $ 0.2 (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)	3 Months Ended
	Dec. 31, 2017
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: December 31, 2017 September 30, 2017 Fair Value Carrying Value Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ 0.3 $ 0.3 $ 0.9 $ 0.9 Liabilities Forward Exchange Contracts $ 0.1 $ 0.1 $ 1.5 $ 1.5 Long-term Debt Senior Notes $ 456.9 $ 425.0 $ 450.5 $ 425.0 Term Facility 571.7 567.8 575.7 569.3 Total Long-term Debt $ 1,028.6 $ 992.8 $ 1,026.2 $ 994.3

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Dec. 31, 2017
Compensation and Retirement Disclosure [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 December 31, 2017 2016 (In millions) Service cost $ 0.5 $ 0.6 Interest cost 0.2 0.1 Actuarial loss amortization — 0.1 Net periodic pension cost $ 0.7 $ 0.8
Defined Contribution Expense	The following table summarizes our defined contribution expense: Three Months Ended December 31, 2017 2016 (In millions) Defined contribution expense $ 2.1 $ 1.9

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Cost Recognized	Share-based compensation awards cost recognized in the consolidated income statement is summarized below: Three Months Ended December 31, 2017 2016 (In millions) Before-Tax Share-Based Compensation Award Cost $ 2.4 $ 1.6 Income Tax Benefit 0.6 0.5 After-Tax Share-Based Compensation Award Cost $ 1.8 $ 1.1
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 December 31, 2017 2016 (In millions) Restricted stock units $ 2.3 $ 1.5 Stock options — 0.1 Director awards 0.1 — Before-Tax Share-Based Compensation Cost $ 2.4 $ 1.6
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 three months ended December 31, 2017 and 2016 used the following assumptions: Three Months Ended December 31, 2017 2016 (In percentages) Expected volatility 28.0 % 28.7 % Risk-free interest rate 1.9 % 1.4 % Expected dividend yield 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) Outstanding, September 30, 2017 1.1 $ 25.30 Granted 0.2 48.39 Paid out (0.2 ) 29.68 Outstanding, December 31, 2017 1.1 $ 29.31 Shares Weighted Average Grant-Date Fair Value (In millions, except weighted average) Outstanding, September 30, 2016 — $ — Converted on October 1, 2016 0.5 22.85 Granted 0.7 25.30 Paid out (0.1 ) 15.55 Outstanding, December 31, 2016 1.1 $ 25.18
Summary of Stock Option Activity	A summary of stock option activity is presented below: Shares Weighted Average Exercise Price (In millions, except weighted average) Outstanding, September 30, 2017 0.5 $ 18.55 Granted — — Exercised — — Outstanding, December 31, 2017 0.5 $ 18.56 Shares Weighted Average Exercise Price (In millions, except weighted average) Outstanding, September 30, 2016 — $ — Converted on October 1, 2016 0.5 18.37 Granted — — Exercised — — Outstanding, December 31, 2016 0.5 $ 18.36 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, December 31, 2017 5.4 $ 9.1 Exercisable, December 31, 2017 5.4 9.1 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, December 31, 2016 6.1 $ 5.1 Exercisable, December 31, 2016 6.0 5.1

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss	The table below summarizes changes in accumulated other comprehensive 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, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 ) Other comprehensive income before reclassifications 0.1 19.7 — 19.8 Net transfers from Air Products — — — — Amounts reclassified from AOCL — — — — Net current period other comprehensive income 0.1 19.7 — 19.8 Other comprehensive income attributable to non-controlling interest — 0.7 — 0.7 Balance, December 31, 2017 $ (0.1 ) $ 3.0 $ (2.2 ) $ 0.7 Net loss on derivatives qualifying as hedges Foreign currency translation adjustments Pension and postretirement benefits Total (In millions) Balance, September 30, 2016 $ (0.2 ) $ (9.8 ) $ — $ (10.0 ) Other comprehensive loss before reclassifications (3.4 ) (33.9 ) — (37.3 ) Net transfers from Air Products — 3.8 (5.6 ) (1.8 ) Amounts reclassified from AOCL 3.4 — 0.1 3.5 Net current period other comprehensive loss — (30.1 ) (5.5 ) (35.6 ) Other comprehensive loss attributable to non-controlling interest — (1.0 ) — (1.0 ) Balance, December 31, 2016 $ (0.2 ) $ (38.9 ) $ (5.5 ) $ (44.6 )
Reclassification out of Accumulated Other Comprehensive Loss	The table below summarizes the reclassifications out of accumulated other comprehensive loss and the affected line item on the consolidated income statements: Three Months Ended December 31, 2017 2016 (In millions) Pension and Postretirement Benefits, net of tax (A) $ — $ 0.1 (A) The components include actuarial loss amortization and are reflected in net periodic benefit cost. Refer to Note 10 , Retirement Benefits , for further information.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 2016 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 18.6 $ 50.8 Denominator Weighted average number of common shares - Basic 108.9 108.7 Effect of dilutive securities Employee stock option and other award plans 0.8 0.5 Weighted average number of common shares - Diluted 109.7 109.2 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 0.17 $ 0.47 Net Income Attributable to Versum - Diluted 0.17 0.47

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	Three Months Ended December 31, 2017 2016 (In millions) Sales Materials $ 214.6 $ 208.0 Delivery Systems and Services 115.3 61.9 Corporate 0.9 0.9 Total $ 330.8 $ 270.8 Operating Income (Loss) Materials $ 65.8 $ 72.9 Delivery Systems and Services 33.4 12.4 Corporate (8.5 ) (3.0 ) Segment Total $ 90.7 $ 82.3 Business separation, restructuring and cost reduction actions (1.8 ) (3.2 ) Total $ 88.9 $ 79.1
Assets	December 31, 2017 September 30, 2017 (In millions) Total Assets Materials $ 805.5 $ 773.8 Delivery Systems and Services 135.7 110.9 Corporate 380.9 362.1 Total $ 1,322.1 $ 1,246.8

Basis of Presentation and Maj37

Basis of Presentation and Major Accounting Policies (Details)	3 Months Ended
	Dec. 31, 2017segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of primary operating segments	2

Business Separation, Restruct38

Business Separation, Restructuring, and Cost Reduction Actions (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Net restructuring charge (gain)	$ (1.8)	$ (3.2)

Business Separation, Restruct39

Business Separation, Restructuring, and Cost Reduction Actions (Details) $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 4.2
Current Period Charge	0.2
Cash Payments	(1.1)
Restructuring reserve, ending balance	3.3
Severance and Other Benefits
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	4.2
Current Period Charge	0.2
Cash Payments	(1.1)
Restructuring reserve, ending balance	$ 3.3

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Inventories at FIFO cost
Finished goods	$ 95.1	$ 87.6
Work in process	23.2	20.3
Raw materials, supplies and other	56	52.5
Inventories at FIFO cost	174.3	160.4
Less: Excess of FIFO cost over LIFO cost	(9)	(8.8)
Inventories	$ 165.3	$ 151.6

Goodwill (Details)

Goodwill (Details) $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 182.6
Currency translation adjustment	3.1
Goodwill, ending balance	185.7
Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	165.3
Currency translation adjustment	2.7
Goodwill, ending balance	168
Delivery Systems and Services
Goodwill [Roll Forward]
Goodwill, beginning balance	17.3
Currency translation adjustment	0.4
Goodwill, ending balance	$ 17.7

Debt - Components of Debt (Deta

Debt - Components of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Debt Disclosure [Abstract]
Short-term borrowings	$ 0	$ 0
Current portion of long-term debt	5.8	5.8
Long-term debt	977.1	977
Total Debt	982.9	$ 982.8
Foreign lines of credit
Short-term Debt [Line Items]
Availability under line of credit	$ 20.7

Debt - Components of Long Term

Debt - Components of Long Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Total debt	$ 992.8	$ 994.3
Less debt discount	2.1	2.5
Less deferred debt costs	7.8	9
Less current portion of long-term debt	5.8	5.8
Long-term debt payable after one year	$ 977.1	977
Term loan facility under Credit Agreement
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.69%
Total debt	$ 567.8	569.3
Line of Credit | Revolving facility under Credit Agreement
Debt Instrument [Line Items]
Total debt	0	0
Senior Notes | 5.500% 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 ($)	Dec. 31, 2017USD ($)
Term Facility
Debt Instrument [Line Items]
Debt instrument, face amount		$ 575,000,000
Effective interest rate (as percent)			3.69%
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 | 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	2	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	Feb. 08, 2018	Dec. 31, 2017	Sep. 30, 2018	Oct. 01, 2018	Sep. 30, 2017	Oct. 01, 2016
Income Tax Examination [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%
Net expense in consolidated income statements related to change in tax law		$ 37.6
Expense related to repatriation tax and future repatriation effect on foreign investments		49
Tax Cuts And Jobs Act Of 2017 Change In Tax Rate Deferred Tax Liability Income Tax Expense Benefit		11.4
Income taxes payable		$ 51.7			$ 31.4
Undistributed foreign earnings, tax						$ 1.2
Subsequent Event [Member]
Income Tax Examination [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%		24.50%
Tax Act Additional Federal Portion of the Liability to be Paid in Cash			$ 3.8
US Interest Expense Deduction Limit beginning fiscal year 2019				30.00%

Financial Instruments (Details)

Financial Instruments (Details) - Derivative Designated as Hedging Instruments $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)derivative_instrument	Dec. 31, 2016	Sep. 30, 2017USD ($)derivative_instrument
Derivative [Line Items]
Number of derivatives | derivative_instrument	0		0
Cash Flow Hedge | Forward exchange contracts
Derivative [Line Items]
Maximum remaining term	9 months	9 months
Notional amount | $	$ 32.1		$ 158.4

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	Dec. 31, 2017	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 0.3	$ 0.9
Derivative Liability	$ 0.1	$ 1.5

Financial Instruments - Gain or

Financial Instruments - Gain or Loss Related to Forward Contracts (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	$ 0.2

Fair Value (Details)

Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	$ 1,028.6	$ 1,026.2
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	992.8	994.3
Level 2 | Fair Value | Term Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	571.7	575.7
Level 2 | Carrying Value | Term Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	567.8	569.3
Level 2 | Forward Exchange Contracts | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Forward Exchange Contracts	0.3	0.9
Liabilities, Forward Exchange Contracts	0.1	1.5
Level 2 | Forward Exchange Contracts | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Forward Exchange Contracts	0.3	0.9
Liabilities, Forward Exchange Contracts	0.1	1.5
Level 1 | Fair Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term Debt	456.9	450.5
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
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 0.6
Interest cost	0.2	0.1
Actuarial loss amortization	0	0.1
Net periodic pension cost	$ 0.7	$ 0.8

Retirement Benefits - Defined B

Retirement Benefits - Defined Benefit Contribution (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Defined contribution expense	$ 2.1	$ 1.9

Share-Based Compensation (Detai

Share-Based Compensation (Details)	Oct. 01, 2016	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares) | shares		0	0
Closing stock price (in dollars per share) | $ / shares		$ 37.85	$ 28.07
Total intrinsic value of stock options exercised		$ 0
Unrecognized compensation cost related to non-vested stock options		0	$ 100,000
Allocated Share-based Compensation Expense		$ 2,400,000	$ 1,600,000
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period		3 years
Vesting period		4 years
Shares granted (in shares) | shares		200,000	700,000
Weighted average grant-date fair value (in dollars per share) | $ / shares		$ 48.39	$ 25.30
Share-based compensation costs paid		$ 0
Unrecognized compensation cost related to restricted stock units		$ 21,200,000	$ 21,000,000
Weighted average period to recognize compensation costs		2 years 7 months 6 days	3 years 2 months 12 days
Total fair value of shares paid out		$ 5,000,000	$ 1,500,000
Allocated Share-based Compensation Expense		$ 2,300,000	$ 1,500,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Weighted average period to recognize compensation costs		0 years	10 months 24 days
Exercise period		10 years
Allocated Share-based Compensation Expense		$ 0	$ 100,000
Director Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual Director Award		100,000,000
Allocated Share-based Compensation Expense		$ 100,000	$ 0
Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares) | shares		3,200,000
Long-Term Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares) | shares			424,247
Weighted average grant-date fair value (in dollars per share) | $ / shares			$ 22.53
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]
Shares granted (in shares) | shares		200,088	304,520
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) | $ / shares		$ 50.18	$ 29.68
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) | $ / shares		$ 45.71	$ 28.37
Air Products
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock split conversion ratio	0.5

Share-Based Compensation - Comp

Share-Based Compensation - Compensation Awards Cost Recognized (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Before-Tax Share-Based Compensation Award Cost	$ (2.4)	$ (1.6)
Income Tax Benefit	0.6	0.5
After-Tax Share-Based Compensation Award Cost	$ 1.8	$ 1.1

Share-Based Compensation - Befo

Share-Based Compensation - Before-tax Share-Based Compensation Award (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	$ 2.4	$ 1.6
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	2.3	1.5
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	0	0.1
Director Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Cost	$ 0.1	$ 0

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	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	28.00%	28.70%
Risk-free interest rate	1.90%	1.40%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.50%	0.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted stock units - $ / shares shares in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding, September 30, 2016 (in shares)	1.1	0
Converted on October 1, 2016 (in shares)		0.5
Paid out (in shares)	0.2	0.7
Forfeited/adjustments (in shares)	(0.2)	(0.1)
Outstanding at June 30, 2017 (in shares)	1.1	1.1
Weighted Average Grant-Date Fair Value
Outstanding, September 30, 2016 (in dollars per share)	$ 25.30	$ 0
Granted (in dollars per share)		22.85
Paid out (in dollars per share)	48.39	25.30
Forfeited/adjustments (in dollars per share)	29.68	15.55
Outstanding at June 30, 2017 (in dollars per share)	$ 29.31	$ 25.18

Share-Based Compensation - Su57

Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding, September 30, 2016 (in shares)	500,000	0
Converted on October 1, 2016 (in shares)		500,000
Exercised (in shares)	0	0
Forfeited (in shares)	0	0
Outstanding at March 31, 2017 (in shares)	500,000	500,000
Weighted Average Exercise Price
Outstanding, September 30, 2016 (in dollars per share)	$ 18.55	$ 0
Converted on October 1, 2016 (in dollars per share)		18.37
Exercised (in dollars per share)	0	0
Forfeited (in dollars per share)	0	0
Outstanding at March 31, 2017 (in dollars per share)	$ 18.56	$ 18.36
Weighted average remaining contractual terms, options outstanding	5 years 4 months 24 days	6 years 1 month 6 days
Aggregate intrinsic value, options outstanding	$ 9.1	$ 5.1
Weighted average remaining contractual terms, options exercisable	5 years 4 months 24 days	6 years
Aggregate intrinsic value, options exercisable	$ 9.1	$ 5.1

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ 24.6	$ (103.4)
Other comprehensive loss before reclassifications	19.8	(37.3)
Net transfers from Air Products	0	(1.8)
Amounts reclassified from AOCL	0	3.5
Total Other Comprehensive Income (Loss)	19.8	(35.6)
Other comprehensive loss attributable to non-controlling interest	0.7	(1)
Stockholders' equity, ending balance	59.7	(134.2)
Accumulated other comprehensive loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(18.4)	(10)
Stockholders' equity, ending balance	0.7	(44.6)
Net loss on derivatives qualifying as hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(0.2)	(0.2)
Other comprehensive loss before reclassifications	0.1	(3.4)
Net transfers from Air Products	0	0
Amounts reclassified from AOCL	0	3.4
Total Other Comprehensive Income (Loss)	0.1	0
Other comprehensive loss attributable to non-controlling interest	0	0
Stockholders' equity, ending balance	(0.1)	(0.2)
Foreign currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(16)	(9.8)
Other comprehensive loss before reclassifications	19.7	(33.9)
Net transfers from Air Products	0	3.8
Amounts reclassified from AOCL	0	0
Total Other Comprehensive Income (Loss)	19.7	(30.1)
Other comprehensive loss attributable to non-controlling interest	0.7	(1)
Stockholders' equity, ending balance	3	(38.9)
Pension and postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(2.2)	0
Other comprehensive loss before reclassifications	0	0
Net transfers from Air Products	0	(5.6)
Amounts reclassified from AOCL	0	0.1
Total Other Comprehensive Income (Loss)	0	(5.5)
Other comprehensive loss attributable to non-controlling interest	0	0
Stockholders' equity, ending balance	$ (2.2)	$ (5.5)

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Postretirement Benefits, net of tax	$ 0	$ 3.5
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	$ 0.1

Stockholders' Equity - Cash Div

Stockholders' Equity - Cash Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Quarterly cash dividend declared (usd per share)	$ 0.05
Cash dividends paid	$ 5.5
Payments of Dividends	$ 5.5	$ 0

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net Income Attributable to Versum	$ 18.6	$ 50.8
Denominator
Weighted average number of common shares - Basic (shares)	108.9	108.7
Effect of dilutive securities
Employee stock option and other award plans (shares)	0.8	0.5
Weighted average number of common shares - Diluted (shares)	109.7	109.2
Earnings Per Common Share Attributable to Versum
Net Income Attributable to Versum - Basic (usd per share)	$ 0.17	$ 0.47
Net Income Attributable to Versum - Diluted (usd per share)	$ 0.17	$ 0.47
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)	0.1	0.2

Segment Information (Narrative)

Segment Information (Narrative) (Details)	3 Months Ended
	Dec. 31, 2017segment
Segment Reporting [Abstract]
Number of primary operating segments	2

Segment Information - Segments

Segment Information - Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Segment Reporting Information [Line Items]
Sales	$ 330.8	$ 270.8
Business separation, restructuring and cost reduction actions	(1.8)	(3.2)
Operating Income (Loss)	88.9	79.1
Total Assets	1,322.1		$ 1,246.8
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)	90.7	82.3
Operating Segments | Materials
Segment Reporting Information [Line Items]
Sales	214.6	208
Operating Income (Loss)	65.8	72.9
Total Assets	805.5		773.8
Operating Segments | Delivery Systems and Services
Segment Reporting Information [Line Items]
Sales	115.3	61.9
Operating Income (Loss)	33.4	12.4
Total Assets	135.7		110.9
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Sales	0.9	0.9
Operating Income (Loss)	(8.5)	(3)
Total Assets	380.9		$ 362.1
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation, restructuring and cost reduction actions	$ (1.8)	$ (3.2)

Subsequent Event (Details)

Subsequent Event (Details) - $ / shares	Jan. 29, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Quarterly cash dividend declared (usd per share)		$ 0.05
Subsequent event
Subsequent Event [Line Items]
Quarterly cash dividend declared (usd per share)	$ 0.05