Versum Materials (VSM) 10-K 22 Nov 17 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Sep. 30, 2017	Nov. 10, 2017	Mar. 31, 2017
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-K
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		108,816,851
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 3.3

ANNUAL CONSOLIDATED INCOME STAT

ANNUAL CONSOLIDATED INCOME STATEMENTS - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Cost of sales	171.9	159.6	154.5	150.9	138.7	135.9	132.5	132.4	636.9	539.5	616.5
Selling and administrative	31.5	34.5	29.5	30.2	33.2	27.3	25.7	23.6	125.7	109.8	109.6
Research and development	12	11.9	10.9	10.3	11.5	11.3	10.2	10.9	45.1	43.9	40.7
Business separation, restructuring and cost reduction actions	10.2	6	6.1	3.2	2.5	1.1	(1.8)	(0.9)	25.5	0.9	21.6
Other (income) expense, net	(1.2)	(2.2)	(0.1)	(2.9)	(0.5)	(0.3)	(1)	(1.1)	(6.4)	(2.9)	(1.1)
Operating Income	70.1	81	69.9	79.1	63	67.4	67.9	80.6	300.1	278.9	222
Equity affiliates’ income	0	0	0	0	0	0	0	0.2	0	0.2	1
Interest expense	12.4	11.9	11.6	11.5	0.4	0	0	0	47.4	0.4	0.1
Income Before Taxes	57.7	69.1	58.3	67.6	62.6	67.4	67.9	80.8	252.7	278.7	222.9
Income tax provision	11.6	14.4	11.5	15.3	15.6	17.6	12.2	13.4	52.8	58.8	31.7
Net Income	46.1	54.7	46.8	52.3	47	49.8	55.7	67.4	199.9	219.9	191.2
Less: Net Income Attributable to Non-controlling Interests	1.5	2	1.9	1.5	1.8	2	1.9	2.2	6.9	7.9	7.1
Net Income Attributable to Versum	$ 44.6	$ 52.7	$ 44.9	$ 50.8	$ 45.2	$ 47.8	$ 53.8	$ 65.2	$ 193	$ 212	$ 184.1
Net income attributable to Versum per common share:
Net Income Attributable to Versum - Basic									$ 1.78	$ 1.95	$ 1.69
Net Income Attributable to Versum - Diluted									$ 1.76	$ 1.95	$ 1.69
Shares used in computing per common share amounts:
Weighted average number of common shares - Basic									108.7	108.7	108.7

ANNUAL CONSOLIDATED COMPREHENSI

ANNUAL CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 199.9	$ 219.9	$ 191.2
Other Comprehensive Income (Loss), net of tax
Translation adjustments, net of tax of $0, $0, and $0.7	(4.9)	22.8	(48.4)
Pension activity, net of tax of $0.5, $0, and $0	(2.2)	0	0
Total Other Comprehensive Income (Loss)	(7.1)	22.8	(48.4)
Comprehensive Income	192.8	242.7	142.8
Net Income Attributable to Non-controlling Interests	6.9	7.9	7.1
Other Comprehensive Loss Attributable to Non-controlling Interests	1.3	0	(2.1)
Comprehensive Income Attributable to Versum	$ 184.6	$ 234.8	$ 137.8

ANNUAL CONSOLIDATED COMPREHENS4

ANNUAL CONSOLIDATED COMPREHENSIVE INCOME STATEMENTS (Parentheticals) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Translation adjustments, tax	$ 0	$ 0	$ 0.7
Pension activity, tax	$ 0.5	$ 0	$ 0

ANNUAL CONSOLIDATED BALANCE SHE

ANNUAL CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Current Assets
Cash and cash items	$ 271.4	$ 105.6
Restricted cash	0	69.6
Trade receivables, net	145.3	130
Inventories	151.6	127.4
Contracts in progress, less progress billings	15.6	19.2
Prepaid expenses	12.2	3.8
Other current assets	10.8	12.4
Total Current Assets	606.9	468
Plant and equipment, net	330.3	296.5
Goodwill	182.6	180.1
Intangible assets, net	70.8	74.8
Other noncurrent assets	56.2	24.4
Total Non-current Assets	639.9	575.8
Total Assets	1,246.8	1,043.8
Current Liabilities
Payables and accrued liabilities	120.8	85.8
Accrued income taxes	31.4	12.7
Current portion of long-term debt	5.8	5.8
Total Current Liabilities	158	104.3
Long-term debt	977	980.3
Deferred tax liabilities	37.3	42.8
Other noncurrent liabilities	49.9	19.8
Total Non-current Liabilities	1,064.2	1,042.9
Total Liabilities	1,222.2	1,147.2
Commitments and Contingencies
Air Products’ net investment	0	(127.3)
Common stock (par value $1 per share; 250,000,000 shares; outstanding 108,815,330)	108.8	0
Capital in excess of par	4.8	0
Air Products’ net investment	(105.2)	0
Accumulated other comprehensive income (loss)	(18.4)	(10)
Total Versum’s Stockholders’ Deficit	(10)	(137.3)
Non-controlling Interests	34.6	33.9
Total Stockholders’ Equity (Deficit)	24.6	(103.4)
Total Liabilities and Stockholders’ Equity (Deficit)	$ 1,246.8	$ 1,043.8
Common Stock, Par or Stated Value Per Share	$ 1
Common Stock, Shares Authorized	250,000,000
Common Stock, Shares, Outstanding	108,815,330

ANNUAL CONSOLIDATED STATEMENTS

ANNUAL CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Activities
Net income	$ 199.9	$ 219.9	$ 191.2
Less: Net Income Attributable to Non-controlling Interests	6.9	7.9	7.1
Net Income Attributable to Versum	193	212	184.1
Adjustments to reconcile income to cash provided by operating activities:
Depreciation and amortization	46	46.9	56.9
Deferred income taxes	2.8	(0.1)	(0.4)
Undistributed earnings of unconsolidated affiliates	0	(0.2)	(0.5)
Gain on sale of assets	(2)	(1)	(0.6)
Share-based compensation	8.3	5	4.7
(Gain) loss on sale of long-lived assets associated with restructuring	0	(3.2)	7.2
Other adjustments	5.9	0.6	6.9
Working capital changes that provided (used) cash:
Trade receivables	(16.3)	(2.1)	(3.4)
Inventories	(22.6)	0.3	(0.7)
Contracts in progress, less progress billings	4.4	(9.2)	20.7
Payables and accrued liabilities	16.5	(5.1)	4.1
Accrued income taxes	5.9	11	(4.7)
Other working capital	20.6	(1.5)	0.1
Cash Provided by Operating Activities	262.5	253.4	274.4
Investing Activities
Additions to plant and equipment	(64)	(35.8)	(22.1)
Proceeds from sale of assets and investments	3.6	43.4	2.4
Acquisition of business	(13.2)	0	0
Transfer to restricted cash	0	(69.5)	0
Cash Used for Investing Activities	(73.6)	(61.9)	(19.7)
Financing Activities
Proceeds from issuance of long-term debt	0	572.1	0
Payments on long-term debt	(5.8)	0	(5.1)
Debt issuance costs	(1.7)	(9.3)	0
Net transfers to Air Products	0	(660.7)	(270.4)
Dividends paid to shareholders	(10.9)	0	0
Dividends paid to non-controlling interests	(7.6)	(7.6)	(9.8)
Other financing activities	1.3	0	0
Cash Used for Financing Activities	(24.7)	(105.5)	(285.3)
Effect of Exchange Rate Changes on Cash	1.6	1.8	(1.2)
Increase (Decrease) in Cash and Cash Items	165.8	87.8	(31.8)
Cash and Cash items-Beginning of Year	105.6	17.8	49.6
Cash and Cash items-End of Period	271.4	105.6	17.8
Cash paid for interest on debt	$ 43.1	$ 0	$ 0

ANNUAL CONSOLIDATED STATEMENTS7

ANNUAL CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY AND NONCONTROLLING INTERESTS - 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, 2014	$ 873.4	$ 0	$ 0	$ 0	$ 822.5	$ 13.5	$ 836	$ 37.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	191.2			0	184.1		184.1	7.1
Net transfers to Air Products	(270.4)				(269.8)		(269.8)	(0.6)
Other comprehensive income (loss)	(48.4)					(46.3)	(46.3)	(2.1)
Other Comprehensive Income (Loss), Net of Tax	(48.4)
Share-based compensation	4.7				4.7		4.7
Dividends to non-controlling interests	(9.8)							(9.8)
Stockholders' equity, ending balance at Sep. 30, 2015	740.7	0	0	0	741.5	(32.8)	708.7	32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	219.9			0	212		212	7.9
Net transfers to Air Products	(1,084.2)				(1,085.8)		(1,085.8)	1.6
Other comprehensive income (loss)	22.8					22.8	22.8	0
Other Comprehensive Income (Loss), Net of Tax	22.8
Share-based compensation	5				5		5
Dividends to non-controlling interests	(7.6)							(7.6)
Stockholders' equity, ending 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	199.9			193	0		193	6.9
Net transfers to Air Products	(165.1)			(298.2)	135.4	(2.4)	(165.2)	0.1
Reclassification of Air Products' net investment to additional paid in capital			8.1		(8.1)
Cash dividend paid	(10.9)		(10.9)				(10.9)
Issuance of common stock at separation	108.7	108.7					108.7
Issuance of common stock through shared based compensation plans	0.1	0.1					0.1
Other comprehensive income (loss)	(4.7)					(6)	(6)
Other Comprehensive Income (Loss), Net of Tax	(7.1)							1.3
Share-based compensation	7.6		7.6				7.6
Dividends to non-controlling interests	(7.6)							(7.6)
Stockholders' equity, ending balance at Sep. 30, 2017	$ 24.6	$ 108.8	$ 4.8	$ (105.2)	$ 0	$ (18.4)	$ (10)	$ 34.6

Basis of Presentation

Basis of Presentation	12 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	1. BASIS OF PRESENTATION On September 16, 2015, the Air Products and Chemicals, Inc. (“Air Products”) Board of Directors announced its intention to separate (the “Separation”) Air Products’ Materials Technologies business, into a newly formed company, Versum Materials, LLC. In September 2016, Versum Materials, LLC was converted from a limited liability company to a Delaware corporation, Versum Materials, Inc. On October 1, 2016, Air Products completed the Separation by distributing to its stockholders one share of common stock of Versum for every two shares of Air Product’s common stock in a distribution intended to be tax-free to Air Products stockholders (the “Distribution”). As a result of the Distribution, Versum is now an independent public company and its common stock is listed under the symbol “VSM” on the New York Stock Exchange. We are a global business that provides innovative solutions for specific customer applications within niche markets based upon expertise in specialty materials. Our business employs applications technology to provide solutions to the semiconductor industry through chemical synthesis, analytical technology, process engineering, and surface science. We are comprised of two primary operating segments, Materials and Delivery Systems and Services, under which we manage our operations and assess performance, and a Corporate segment. Prior to the Separation, the accompanying Annual Consolidated Financial Statements of Versum, were prepared on a stand-alone basis and were derived from Air Products’ consolidated financial statements and accounting records where Versum was a division of Air Products. For all periods presented, the Annual Consolidated Financial Statements were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Versum. All significant intercompany transactions and balances have been eliminated in the preparation of the accompanying Annual Consolidated Financial Statements. Prior to the Separation, transactions between Versum and Air Products were reflected in the annual consolidated balance sheets as “Air Products’ net investment” and in the annual consolidated statements of cash flows as a financing activity in “Net transfers (to) from Air Products.” Prior to the Separation, Air Products provided us with centrally managed services and corporate functions. Accordingly, certain shared costs including but not limited to administrative expenses for information technology, general services, human resources, legal, accounting and other services, had been allocated to us and were reflected as expenses in the Annual Consolidated Financial Statements. Expenses had been allocated on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed costs, revenue, operating income or headcount. We consider the expense allocation methodology and results to be reasonable and consistently applied for all periods presented prior to the Separation. After the Separation, Versum has performed most of these functions using its own resources or purchased services. However, the remainder of these functions continue to be provided by Air Products under various agreements. See Note 4 , Related Party Transactions , for a description of the agreements between Versum and Air Products. For periods prior to October 1, 2016, the annual consolidated balance sheets of Versum included Air Products’ assets and liabilities that were specifically identifiable or were otherwise transferred to us, including subsidiaries and affiliates in which Air Products had a controlling financial interest. Also included within our Annual Consolidated Financial Statements were the results of certain product lines which had historically been managed by us but were retained by Air Products after the Separation. These product lines represented approximately 1% and 1% of annual combined sales and operating income, respectively, for fiscal year 2016. Air Products performed cash management and other treasury-related functions on a centralized basis for nearly all of its legal entities. Substantially all cash generated by our business was remitted to Air Products prior to the Separation and therefore accounted for through Air Products’ net investment in the Annual Consolidated Financial Statements. Accordingly, Air Products had not allocated any centrally managed cash and cash items to us in the Annual Consolidated Financial Statements prior to the Separation. Air Products’ debt and related interest expense had not been allocated to us for any of the periods presented since we were not the legal obligor of the debt, and Air Products’ borrowings were not directly attributable to us. There were no other financing arrangements between us and Air Products during the periods presented. For periods prior to the Separation, Versum’s income tax expense was calculated using the separate return method as if Versum was a separate taxpayer. The majority of the accrued U.S. federal, state, and foreign income tax balances were treated as settled with Air Products as of the end of each year. After the Separation, income tax expense and income tax balances represent Versum’s federal, state and foreign income taxes as an independent company.

Major Accounting Policies

Major Accounting Policies	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Major Accounting Policies	2. MAJOR ACCOUNTING POLICIES Estimates and Assumptions The preparation of the Annual Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the Annual Consolidated Financial Statements and accompanying notes, including allocations of costs during the reporting period. Management’s estimates are based on historical experience, facts and circumstances available at the time, and various other assumptions that are believed to be reasonable. Actual results could differ from those estimates. Revenue Recognition Revenue from product sales is recognized as risk and title to the product transfer to the customer (which generally occurs at the time shipment is made), the sales price is fixed or determinable, and collectability is reasonably assured. Sales returns and allowances are generally not a business practice in the industry. We use both the completed contract and percentage-of-completion methods to record revenue from equipment sale contracts. The completed contract method is used in circumstances in which financial position and results of operations are not materially different from those resulting from use of the percentage-of-completion method, e.g., certain short-term contracts. We use the percentage-of-completion method when we can make reasonably dependable estimates of progress toward completion and performance is expected. Under the percentage-of-completion method, revenue from the sale of major equipment is recognized primarily based on costs incurred to date compared with total estimated costs. Under the completed contract method, revenue and cost is recognized when the equipment is completed and transferred to the customer. Changes to estimated labor hours under the percentage-of-completion method or anticipated losses under either method, if any, are recognized in the period determined. Revenue from on-site services are generally fixed monthly fee arrangements for which we recognize revenue as the services are performed. Amounts billed for shipping and handling fees are classified as sales in the consolidated income statements. Amounts billed for sales and use taxes, value-added taxes, and certain excise and other specific transactional taxes imposed on revenue-producing transactions are presented on a net basis and excluded from sales in the consolidated income statements. We record a liability until remitted to the respective taxing authority. Cost of Sales Cost of sales predominantly represents the cost of tangible products sold. These costs include labor, raw materials, depreciation, production supplies, and materials packaging costs. Costs incurred for shipping and handling are also included in cost of sales. Depreciation Depreciation is recorded using the straight-line method, which deducts equal amounts of the cost of each asset from earnings every year over its expected economic useful life. The principal lives for major classes of plant and equipment are summarized in Note 8 , Plant and Equipment, Net. Selling and Administrative The principal components of selling and administrative expenses are compensation, advertising, and promotional costs. Research and Development Research and development costs are expensed as incurred. Research and development expenses include employee costs, materials, contract services, research agreements, and other external spending related to the discovery and development of new products, enhancement of existing products and regulatory approval of new and existing products. Post-employment Benefits We provide termination benefits to employees as part of ongoing benefit arrangements and record a liability for termination benefits when probable and estimable. These criteria are met when management, with the appropriate level of authority, approves and commits to its plan of action for termination; the plan identifies the employees to be terminated and their related benefits; and the plan is to be completed within one year. We typically do not provide one-time benefit arrangements of significance. Fair Value Measurements We are required to measure certain assets and liabilities at fair value, either upon initial measurement or for subsequent accounting or reporting. For example, fair value is used in the initial measurement of net assets acquired in a business combination; on a recurring basis in the measurement of derivative financial instruments; and on a nonrecurring basis when long-lived assets are written down to fair value when held for sale or determined to be impaired. Refer to Note 13 , “ Fair Value ”, for information on the methods and assumptions used in our fair value measurements. Financial Instruments We address certain financial exposures through a controlled program of risk management that includes the use of derivative financial instruments. If the circumstances qualify and we designate hedge accounting, the hedging relationship between the underlying financial exposures and the related hedging instrument would be documented on the date the derivative is entered into with the counterparty. Our program currently includes the use of forward exchange contracts to hedge intercompany loans denominated in a foreign currency. We have not designated hedge accounting for any of the forward exchange contracts. Foreign Currency Since we do business in many foreign countries, fluctuations in currency exchange rates affect our financial position and results of operations. In certain of our foreign operations, the local currency is considered the functional currency. These foreign subsidiaries translate their assets and liabilities into U.S. dollars at current exchange rates in effect at the end of the fiscal period. The gains or losses that result from this process are shown as translation adjustments in accumulated other comprehensive income (loss) in the stockholders’ equity section of the annual consolidated balance sheets. The revenue and expense accounts of these foreign subsidiaries are translated into U.S. dollars at the average exchange rates that prevail during the period. Therefore, the U.S. dollar value of these items on the income statement fluctuates from period to period, depending on the value of the dollar against foreign currencies. Some transactions are made in currencies different from an entity’s functional currency. Gains and losses from these foreign currency transactions are generally included in other income (expense), net on our consolidated income statements as they occur. Litigation Accruals for litigation are made when the information available indicates that it is probable that a liability has been incurred and the amount can be reasonably estimated. When only a range of possible loss can be established, the most probable amount in the range is accrued. If no amount within this range is a better estimate than any other amount within the range, the minimum amount in the range is accrued. The accrual for a litigation loss contingency includes estimates of potential damages and other directly related costs expected to be incurred. Litigation liabilities and expenditures included in the Annual Consolidated Financial Statements were not material for the periods presented. Share-Based Compensation Prior to the Separation, our employees participated in Air Products’ share-based compensation plans, which included stock options, deferred stock units, and restricted stock. Prior to the Separation, the Annual Consolidated Financial Statements included share-based compensation expense associated with our employees and Air Products’ costs that had been allocated to us based on awards and terms previously granted. 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. The grant-date fair value of awards is expensed over the vesting period during which employees perform related services. Expense recognition is accelerated for retirement-eligible individuals who would meet the requirements for vesting of awards upon their retirement. The Black Scholes model is utilized to value new stock option awards. The grant date fair value of the deferred stock units tied to a market condition is estimated using a Monte Carlo simulation model for new awards. Income Taxes For the fiscal years ended September 30, 2016 and 2015, certain of our operations included in our Annual Consolidated Financial Statements were divisions of legal entities included in Air Products consolidated U.S. federal and state income tax returns, or tax returns of non-U.S. subsidiaries of Air Products. The provision for income taxes and related annual consolidated balance sheet accounts of such entities, for such periods, have been prepared and presented in the Annual Consolidated Financial Statements based on a stand-alone basis separate from Air Products. Differences between our separate return income tax provision and cash flows attributable to income taxes for operations that were divisions of legal entities have been recognized as capital contributions from, or dividends to, Air Products, within Air Products’ net investment. As a stand-alone entity, our deferred taxes and effective tax rate differ from those in historical periods. We account for income taxes under the liability method. Under this method, deferred tax assets and liabilities are recognized for the tax effects of temporary differences between the financial reporting and tax bases of assets and liabilities measured using enacted tax rates. The cumulative impact of a change in tax rates or regulations is included in income tax expense in the period that includes the enactment date. A tax benefit for an uncertain tax position is recognized when it is more likely than not that the position will be sustained upon examination based on its technical merits. This position is measured as the largest amount of tax benefit that is greater than 50% likely of being realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense. For the fiscal years ended September 30, 2016 and 2015, the majority of the accrued U.S. federal, state, and foreign income tax balances were treated as settled with Air Products as of the end of each year. Therefore, they are included in Air Products’ net investment in the Annual Consolidated Financial Statements, for such periods. Non-controlling Interests We consolidate investments that we control but do not wholly own. The Annual Consolidated Financial Statements include all assets, liabilities, revenues, and expenses of our joint venture in Taiwan for which we have a 74% ownership interest during the periods presented in the Annual Consolidated Financial Statements. The ownership interests held by third party non-controlling partners are presented as non-controlling interests in our annual consolidated balance sheets. Any net income or loss attributed to the non-controlling partners is presented as such in the consolidated income statements. The activity for non-controlling interests for the years ended September 30, 2017 , 2016 and 2015 is presented in the annual consolidated statements of stockholders’ equity. Cash and Cash Items Cash and cash items generally include cash, time deposits, and certificates of deposit acquired with an original maturity of three months or less for our foreign entities. Prior to the Separation, cash was managed centrally at Air Products and most cash generated by our business was remitted to Air Products. Such centralized cash management transactions relating to our business were reflected through Air Products’ net investment. Accordingly, none of the centrally managed cash at the Air Products’ corporate level had been reflected in our Annual Consolidated Financial Statements. Restricted Cash Restricted cash consists of cash restricted for payment to Air Products made subsequent to the Separation. Trade Receivables, net Trade receivables comprise amounts owed to us through our operating activities and are presented net of allowances for doubtful accounts. The allowances for doubtful accounts represent estimated uncollectible receivables associated with potential customer defaults on contractual obligations. A provision for customer defaults is made on a general formula basis when it is determined that the risk of some default is probable and estimable but cannot yet be associated with specific customers. The assessment of the likelihood of customer defaults is based on various factors, including the length of time the receivables are past due, historical experience, and existing economic conditions. The allowance also includes amounts for certain customers where a risk of default has been specifically identified, considering factors such as the financial condition of the customer and customer disputes over contractual terms and conditions. Allowance for doubtful accounts were $1.0 million and $0.8 million as of fiscal year end September 30, 2017 and 2016 , respectively. Provisions to the allowance for doubtful accounts charged against income were not material in fiscal 2017 , 2016 , and 2015 . Inventories Inventories are stated at the lower of cost or market. We write down our inventories for estimated obsolescence or unmarketable inventory based upon assumptions about future demand and market conditions. We utilize the last-in, first-out (“LIFO”) method for determining the cost of inventories in the United States. Inventories outside of the United States are accounted for on the first-in, first-out (“FIFO”) method, as the LIFO method is not generally permitted in the foreign jurisdictions we operate. Equity Investments The equity method of accounting is used when we exercise significant influence but do not have operating control, generally assumed to be 20% to 50% ownership. Under the equity method, original investments are recorded at cost and adjusted by our share of undistributed earnings or losses of these companies. Equity investments are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the investment may not be recoverable. The Annual Consolidated Financial Statements include our investment in and proportionate share of the income from our 20% owned equity affiliate, Daido Air Products Electronics, Inc. During the first quarter of 2016, we sold our investment in this affiliate. Refer to Note 6 , “ Sale of Equity Affiliate ”, for additional information. Plant and Equipment Plant and equipment is stated at cost less accumulated depreciation. Construction costs, labor, and applicable overhead related to installations are capitalized. Expenditures for additions and improvements that extend the lives or increase the capacity of plant assets are capitalized. The costs of maintenance and repairs of plant and equipment are charged to expense as incurred. Fully depreciated assets are retained in the gross plant and equipment and accumulated depreciation accounts until they are removed from service. In the case of disposals, assets and related depreciation are removed from the accounts, and the net amounts, less proceeds from disposal, are included in income. Impairment of Long-Lived Assets Long-lived assets are grouped for impairment testing at the lowest level for which there are identifiable cash flows that are largely independent of the cash flows of other assets and liabilities and are evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable. We assess recoverability by comparing the carrying amount of the asset group to estimated undiscounted future cash flows expected to be generated by the asset group. If an asset group is considered impaired, the impairment loss to be recognized is measured as the amount by which the asset group’s carrying amount exceeds its fair value. Long-lived assets held for sale are reported at the lower of carrying amount or fair value less cost to sell. Goodwill The purchase price is allocated to the assets acquired and liabilities assumed based on their estimated fair market values. Any excess purchase price over the fair market value of the net assets acquired, including identified intangibles, is recorded as goodwill. Preliminary purchase price allocations are made at the date of acquisition and finalized when information needed to affirm underlying estimates is obtained, within a maximum allocation period of one year. Goodwill is subject to impairment testing at least annually. In addition, goodwill is tested more frequently if a change in circumstances or the occurrence of events indicates that potential impairment exists. Intangible Assets Intangible assets with determinable lives primarily consist of customer relationships and purchased patents and technology. The cost of intangible assets with determinable lives is amortized on a straight-line basis over the estimated period of economic benefit. Amortizable lives are adjusted whenever there is a change in the estimated period of economic benefit. No residual value is estimated for intangible assets. Retirement Benefits For periods prior to October 1, 2016, Air Products sponsored defined benefit pension plans, defined contribution plans, and other post-employment benefit plans that are shared amongst its businesses. Prior to the Separation on October 1, 2016, participation of our employees in these plans was reflected in the Annual Consolidated Financial Statements as though Versum participated in a multi-employer plan with Air Products. A proportionate share of cost was reflected in these Annual Consolidated Financial Statements, primarily within selling and administrative expenses. In 2017, certain international pension plans were legally split from Air Products. Our plans provide certain international employees in Germany, Korea and Taiwan who previously participated in the Air Products plans the same defined benefit pension benefits that had previously been provided by Air Products. Versum assumed the defined benefit pension plan assets and liabilities of these plans. Upon Separation from Air Products, our employees’ balances in the Air Products sponsored defined contribution plan was transferred to a Versum defined contribution plan. Air Products’ Net Investment Prior to the Separation, Air Products’ net investment in our business was presented as “Air Products’ net investment” in lieu of stockholders’ equity, as a stand-alone legal and capital structure did not exist for the historical periods presented. Earnings Per Share Prior to the Separation, Versum earnings per share for 2016 and 2015 were calculated using the shares that were distributed to Air Products stockholders immediately following the Separation. For periods prior to the Separation it is assumed that there are no dilutive equity instruments as there were no equity awards in Versum outstanding prior to the Separation.

New Accounting Guidance

New Accounting Guidance	12 Months Ended
	Sep. 30, 2017
Accounting Changes and Error Corrections [Abstract]
New Accounting Guidance	3. NEW ACCOUNTING GUIDANCE Accounting Guidance Implemented Share-Based Compensation In March 2016, the Financial Accounting Standards Board (“FASB”) issued an update to simplify the accounting for employee share-based payments, including the income tax impacts, the classification on the statement of cash flows, and forfeitures. The amendments are effective for fiscal year 2018, with early adoption permitted. As of the first quarter of fiscal year 2017, we have adopted this guidance. Share-Based Compensation In May 2017, the FASB issued guidance which amends the scope of modification accounting for share-based payment arrangements. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. The Company adopted the standard effective October 1, 2017. The adoption is not expected to have a material impact on the Annual Consolidated Financial Statements. Going Concern In August 2014, the FASB issued guidance regarding management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern within one year of the issuance of the financial statements. If substantial doubt exists, additional disclosures would be required. The Company adopted the standard effective October 1, 2017. This guidance did not have a significant impact on our Annual 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 interim and annual reporting periods beginning after December 15, 2017. The components of the net (benefit) cost are shown in Note 15 , “ 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 Annual Consolidated Financial Statements. Goodwill Impairment In January 2017, the 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, 2021, 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 will adopt the standard effective October 1, 2017. The adoption is not expected to have a material impact on the Annual 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 Annual 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 Annual Consolidated Financial Statements. Measurement of Inventory In July 2015, the FASB issued guidance to simplify the measurement of inventory recorded using either the 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 LIFO is not impacted. The guidance is effective for us beginning in fiscal year 2018 and will be applied prospectively, with early adoption permitted. This guidance is not expected to have a significant impact on our Annual 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 and vehicles that are currently accounted for as operating leases as discussed in Note 12 , “ 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 Annual 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 Annual Consolidated Financial Statements.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Related Party Transactions	4. RELATED PARTY TRANSACTIONS Prior to the separation, Air Products provided us with centrally managed services and corporate functions. Accordingly, certain shared costs including but not limited to administrative expenses for information technology, general services, human resources, legal, accounting and other services, had been allocated to us and are primarily reflected as expenses in the Corporate segment in the Consolidated Financial Statements. Expenses had been allocated on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed costs, revenue, operating income, or headcount. We consider the expense allocation methodology and results to be reasonable and consistently applied for all periods presented. Total costs allocated to us in the consolidated income statements are summarized below: Year Ended September 30, 2017 2016 2015 (In millions) Cost of sales $ — $ 2.8 $ 3.6 Selling and administrative — 16.8 17.8 Research and development — 1.0 1.4 Business restructuring and cost reduction actions — 0.7 3.5 Total Allocated Costs $ — $ 21.3 $ 26.3 These allocated costs are reflected in “Air Products’ net investment” and in the consolidated statements of cash flows as a financing activity in “Net transfers (to) from Air Products.” It is not practicable to quantify the amount of expenses that Versum would have incurred on a stand-alone basis for periods prior to the Separation. Prior to the Separation, certain of our employees participated in share-based compensation plans and retirement benefit plans sponsored and administered by Air Products or its affiliates. The costs of these plans associated with our employees are included in the Annual Consolidated Financial Statements, but excluded from the table of allocated costs above. Our consolidated balance sheet at September 30, 2016 does not include the share-based compensation instrument. Agreements with Air Products In connection with the Separation and Distribution, Versum and its affiliates entered into various agreements with Air Products and its affiliates contemplated by the Separation Agreement, including the following agreements: Transition Services Agreement. Under the Transition Services Agreement, Air Products provides certain transition services to us and we provide certain transition services to Air Products. Each party provides these services for a limited time, generally for no longer than 12 to 24 months following the October 1, 2016 Distribution date, for specified fees, which are at cost for services provided by third parties and at cost plus approximately 5% percent for services provided by either us or Air Products, as applicable. Tax Matters Agreement. The Tax Matters Agreement generally governs Air Products’ and Versum’s respective rights, responsibilities and obligations with respect to taxes (including taxes arising in the ordinary course of business and taxes, if any, incurred as a result of any failure of the Distribution or certain related transactions to qualify as tax-free for U.S. federal income tax purposes), tax attributes, the preparation and filing of tax returns, the control of audits and other tax proceedings and other matters regarding taxes for any tax period ending on or before the Distribution date, as well as tax periods beginning after the Distribution date. In addition, the Tax Matters Agreement imposes certain restrictions on us and our subsidiaries (including restrictions on share issuances, business combinations, sales of assets and similar transactions) designed to preserve the tax-free status of the Distribution and certain related transactions. The Tax Matters Agreement includes special rules that allocate tax liabilities in the event the Distribution, or certain related transactions fail to qualify as tax-free for U.S. federal income tax purposes. In general, Versum is liable for taxes incurred by Air Products that may arise if Versum takes, or fails to take, as the case may be, certain actions that may result in the Distribution or certain related transactions failing to qualify as tax-free for U.S. federal income tax purposes. Employee Matters Agreement . The Employee Matters Agreement governs the compensation and employee benefit obligations with respect to our current and former employees and those of Air Products. The Employee Matters Agreement allocates liabilities and responsibilities relating to employee compensation and benefits plans and programs and other related matters in connection with the Distribution including, without limitation, the treatment of outstanding Air Products’ equity awards, other outstanding incentive compensation awards, deferred compensation obligations and retirement and welfare benefit obligations.

Business Separation, Restructur

Business Separation, Restructuring, and Cost Reduction Actions	12 Months Ended
	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Business Separation, Restructuring, and Cost Reduction Actions	5. 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 fiscal year 2017, we recognized a net charge of $25.5 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 fiscal year 2016, we recognized a net gain of $0.7 million . The 2016 net gain included a charge of $2.5 million for severance and other benefits related to the elimination of approximately 90 positions as part of cost reduction actions. In addition, we recognized a gain of $3.2 million on assets that were previously written down to a carrying value of $17.9 million . The gain included $1.4 million related to the sale of the onsite ammonia assets. The majority of these actions pertain to the Materials segment. During fiscal year 2016, we also incurred costs of $1.6 million related to the Separation. In fiscal year 2015, we recognized an expense of $21.6 million . Severance and other benefits totaled $14.4 million , including an allocation of expenses incurred by the parent, and related to the elimination of approximately 260 positions. Asset actions totaled $7.2 million and primarily related to the exit of a product line (onsite ammonia) in the Materials segment, which resulted in the write-down of assets to fair value based on internal estimates, and adjustments to expenses recorded for the 2013 plan actions. In the second quarter of 2016, we sold the onsite ammonia assets for $17.1 million which resulted in a before-tax gain of $1.4 million . The 2015 charges related to the segments as follows: $12.3 million in Materials, $5.8 million in Delivery Systems and Services, and $3.5 million in Corporate. The following table summarizes the carrying amount of the accrual for the business realignment and reorganization at September 30, 2017 : Severance and Other Benefits Asset Actions/Other Total (In millions) September 30, 2014 $ 0.9 $ — $ 0.9 2015 Charge 14.4 7.2 21.6 Cash payments (A) (11.2 ) — (11.2 ) Non-cash expenses — (7.2 ) (7.2 ) September 30, 2015 $ 4.1 $ — $ 4.1 2016 Charge 2.5 (3.2 ) (0.7 ) Cash (payments) receipts (A) (6.0 ) 4.2 (1.8 ) Non-cash expenses — (1.0 ) (1.0 ) September 30, 2016 $ 0.6 $ — $ 0.6 2017 Charge 4.7 — 4.7 Cash payments (1.1 ) — (1.1 ) Non-cash expenses — — — September 30, 2017 $ 4.2 $ — $ 4.2 (A) Cash payments include an allocation of severance and other benefits of Air Products’ employees within its Corporate and other segment which were paid by Air Products.

Sale of Equity Affiliate

Sale of Equity Affiliate	12 Months Ended
	Sep. 30, 2017
Equity Method Investments and Joint Ventures [Abstract]
Sale of Equity Affiliate	6. SALE OF EQUITY AFFILIATE In December 2015, we sold our investment in our equity affiliate, Daido Air Products Electronics, Inc., for $15.9 million , which resulted in a before-tax gain of $0.7 million for the year ended September 30, 2016 . The carrying value at the time of sale included a $12.8 million investment in net assets of and advances to equity affiliates and a $2.4 million foreign currency translation loss that had been deferred in accumulated other comprehensive loss. In addition, the income tax provision, before the valuation allowance, for the year ended September 30, 2016 included an expense of $5.3 million as a result of the sale. In 2015, we recorded $1.0 million of equity affiliates’ income related to this investment.

Inventories

Inventories	12 Months Ended
	Sep. 30, 2017
Inventory Disclosure [Abstract]
Inventories	7. INVENTORIES The components of inventories are as follows: September 30, 2017 2016 (In millions) Inventories at FIFO cost Finished goods $ 87.6 $ 94.0 Work in process 20.3 12.3 Raw materials, supplies and other 52.5 29.4 160.4 135.7 Less: Excess of FIFO cost over LIFO cost (8.8 ) (8.3 ) Inventories $ 151.6 $ 127.4 Inventories valued using the LIFO method comprised 28% and 32% of combined inventories before LIFO adjustment at September 30, 2017 and 2016 , respectively. Liquidation of LIFO inventory layers in 2017 , 2016 , and 2015 did not materially affect the results of operations. First-in, first-out (FIFO) cost approximates replacement cost.

Plant and Equipment, Net

Plant and Equipment, Net	12 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Plant and Equipment, Net	8. PLANT AND EQUIPMENT, NET The major classes of plant and equipment are as follows: September 30, Useful Life in years 2017 2016 (In millions, except useful life) Land $ 21.8 $ 21.9 Buildings 30 149.3 147.1 Machinery and Equipment Production facilities 10 to 15 479.9 433.6 Distribution and other (A) 5 to 25 252.1 255.9 Total machinery and equipment 732.0 689.5 Construction in progress 52.1 26.2 Plant and equipment, at cost 955.2 884.7 Less: accumulated depreciation 624.9 588.2 Plant and equipment, net $ 330.3 $ 296.5 (A) The depreciable lives for various types of distribution equipment are 10 to 25 years for cylinders, depending on the nature and properties of the product, and generally 20 years for other distribution equipment such as tanks and trailers. Depreciation expense was $38.4 million , $39.4 million , and $48.1 million in 2017 , 2016 , and 2015 , respectively. In January 2016, we sold two onsite ammonia plants for $17.1 million , which resulted in a before-tax gain of $1.4 million during the second quarter of 2016. This gain is reflected in business separation, restructuring and cost reduction actions on our income statement. The income tax provision includes an expense of $1.5 million as a result of the sale.

Goodwill

Goodwill	12 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	9. GOODWILL Changes to the carrying amount of goodwill by segment are as follows: Materials Delivery Systems and Services Total (In millions) Balance at September 30, 2015 $ 150.6 $ 16.4 $ 167.0 Currency translation adjustment 12.0 1.1 13.1 Balance at September 30, 2016 $ 162.6 $ 17.5 $ 180.1 Acquisition (Note 23) 5.0 — 5.0 Currency translation adjustment (2.3 ) (0.2 ) (2.5 ) Balance at September 30, 2017 $ 165.3 $ 17.3 $ 182.6 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. We conducted impairment tests in the fourth quarter of 2017 and determined that there was no goodwill impairment. As of the fourth quarter of 2017 , the fair value of each reporting unit exceeded its carrying value.

Intangible Assets

Intangible Assets	12 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	10. INTANGIBLE ASSETS The table below provides details of acquired intangible assets: September 30, 2017 September 30, 2016 Gross Accumulated Amortization Net Gross Accumulated Amortization Net (In millions) Customer relationships $ 79.5 $ (22.7 ) $ 56.8 $ 80.4 $ (19.5 ) $ 60.9 Patents and technology 50.3 (37.9 ) 12.4 46.4 (34.2 ) 12.2 Other 3.2 (1.6 ) 1.6 3.2 (1.5 ) 1.7 Total Intangible Assets $ 133.0 $ (62.2 ) $ 70.8 $ 130.0 $ (55.2 ) $ 74.8 The intangible assets primarily pertain to the Materials segment and have a remaining useful life of approximately 17 years for customer relationships and 5 years for patents and technology. Amortization expense for intangible assets was $7.6 million , $7.5 million , and $8.8 million in 2017 , 2016 , and 2015 , respectively. Projected annual amortization expense for intangible assets as of September 30, 2017 is as follows: 2018 $ 7.2 2019 5.9 2020 5.8 2021 5.8 2022 4.9 Thereafter 41.2 Total $ 70.8 In 2017, Versum acquired the intellectual property and related assets of Dynaloy through a business combination. Refer to Note 23 , " Acquisition ," for further discussion of the related intangible assets and goodwill.

Debt

Debt	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Debt	11. DEBT Components of Debt September 30, 2017 2016 (In millions) Short-term borrowings (A) $ — $ — Current portion of long-term debt 5.8 5.8 Long-term debt 977.0 980.3 Total Debt $ 982.8 $ 986.1 (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 September 30, 2017 is $20.2 million . Long-term Debt September 30, 2017 2016 (In millions) Term loan facility under Credit Agreement $ 569.3 $ 575.0 Revolving facility under Credit Agreement — — 5.500% Senior Notes due 2024 425.0 425.0 Total debt 994.3 1,000.0 Less debt discount 2.5 2.8 Less deferred debt costs 9.0 11.1 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 977.0 $ 980.3 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% (effective rate of 3.83% as of September 30, 2017 ). 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% . 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 September 30, 2017 , we had availability of $200 million under 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 September 30, 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, 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 September 30, 2017 . Maturities Maturities of long-term debt are as follows: Total Debt (In millions) Payments due for the year ended September 30, 2018 $ 5.8 2019 5.8 2020 5.8 2021 5.8 2022 5.8 Thereafter 965.3 Total $ 994.3

Leases

Leases	12 Months Ended
	Sep. 30, 2017
Leases [Abstract]
Leases	12. LEASES Lessee Accounting Operating leases principally relate to real estate and also include distribution equipment and vehicles. Certain leases include escalation clauses, renewal, and purchase options. Rent expense is recognized on a straight-line basis over the minimum lease term. Rent expense under operating leases, including month-to-month agreements, was $12.2 million in 2017 , $7.6 million in 2016 , and $8.4 million in 2015 . At September 30, 2017 , minimum payments due under leases are as follows: (In millions) 2018 $ 10.1 2019 8.3 2020 6.7 2021 4.1 2022 3.0 Thereafter 1.4 Total $ 33.6

Fair Value

Fair Value	12 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value	13. 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 are 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 14 , 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 loan 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: September 30, 2017 Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ 0.9 $ 0.9 Liabilities Forward Exchange Contracts $ 1.5 $ 1.5 Long-term Debt Senior Notes $ 450.5 $ 425.0 Term Loan Facility 575.7 569.3 Total Long-term debt $ 1,026.2 $ 994.3 The carrying amounts reported in the annual 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.

Financial Instruments Financial

Financial Instruments Financial instruments	12 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial instruments	14. FINANCIAL INSTRUMENTS We enter into forward exchange contracts to hedge the fair value exposure on intercompany loans. During the year ended September 30, 2017 , this portfolio of forward exchange contracts consisted primarily of Korean Won and U.S. dollars. The maximum remaining term of any forward exchange contract currently outstanding at September 30, 2017 is approximately 1 year. At September 30, 2017 , the total notional principal amount of our outstanding hedge contracts was $158.4 million . As of September 30, 2017 , there were no derivatives designated as hedging instruments. The table below summarizes the fair values of our derivatives not designated as hedging instruments and balance sheet location of these outstanding derivatives: 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 13 , 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: Year Ended September 30, 2017 (In millions) Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ 2.2 (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.

Retirement Benefits

Retirement Benefits	12 Months Ended
	Sep. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Retirement Benefits	RETIREMENT BENEFITS For periods prior to October 1, 2016, Air Products offered various long-term benefits to our employees through defined benefit pension plans and defined contribution plans. Prior to the Separation on October 1, 2016, participation of our employees in these plans is reflected in the Annual Consolidated Financial Statements as though we participated in a multi-employer plan with Air Products. Defined Benefit Pensions In 2017, certain international pension plans were legally split from Air Products. Our plans provide certain international employees in Germany, Korea and Taiwan who previously participated in the Air Products plans the same defined benefit pension benefits that had previously been provided by Air Products. The following table summarizes the benefit obligation, fair value of the plan assets and the funded status at September 30, 2017 : 2017 (In millions) Change in benefit obligation: Benefit obligation at September 30, 2016 $ — Converted on October 1, 2016 26.5 Service cost 2.3 Interest cost 0.6 Actuarial gain (4.9 ) Benefits paid (1.2 ) Foreign currency impact (0.5 ) Benefit obligation at end of year $ 22.8 Change in plan assets: Fair value of plan assets at September 30, 2016 $ — Converted on October 1, 2016 3.0 Employer contributions 5.0 Benefits paid (1.2 ) Fair value of plan assets at September 30, 2017 $ 6.8 Funded status: Plan assets less than benefit obligation - Net amount recognized $ (16.0 ) Amounts recognized in the annual consolidated balance sheets consist of: 2017 (In millions) Non-current liabilities $ (16.0 ) Accumulated other comprehensive loss, net of taxes (2.2 ) Amounts recognized in accumulated other comprehensive loss, net of tax consist of: 2017 (In millions) Balance at September 30, 2016 $ — Converted on October 1, 2016 (6.2 ) Net loss amortized during the year 0.4 Net gain during the year 3.7 Non-controlling interest (0.1 ) Balance at September 30, 2017 $ (2.2 ) The components of net periodic pension costs for our defined benefit pension plans are as follows: 2017 (In millions) Service cost $ 2.3 Interest cost 0.6 Expected return on plan assets (0.1 ) Actuarial loss amortization 0.5 Net periodic pension cost $ 3.3 The estimated amount that will be amortized from accumulated other comprehensive income into net periodic pension cost in 2018 is $0.1 million . Assumptions used in determining the benefit obligation and net periodic pension cost for the year ended September 30, 2017 are presented in the following table as weighted-averages: 2017 (In millions) Benefit obligations: Discount rate 3.2 % Rate of compensation increase 4.1 % Net Periodic Pension Cost: Discount rate 2.3 % Rate of compensation increase 4.9 % Expected rate of return on plan 2.0 % The discount rate assumption is calculated based on market yields at the valuation date on government bonds and high quality corporate bonds as well as the estimated maturity of benefit payments. The expected rate of return assumption is based on weighted-average expected returns from each asset class. Expected returns reflect a combination of historical performance analysis and current market conditions and include input from our actuaries. The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy discussed in Note 13 , is as follows: 2017 (In millions) Other investments (Level 2) $ 4.1 Insurance contract (Level 3) 2.7 Total $ 6.8 The Other investments category represents accounts our subsidiaries in Taiwan have invested in a government directed Labor Pension Fund in which the return is guaranteed by the government, therefore it is characterized as Other and level 2. The Insurance contract category represents the Korea plan which is funded by an investment with Samsung Insurance and is classified as level 3, as they are carried at contract value which approximates fair value. We expect to make contributions of approximately $0.4 million during 2018. The expected future benefit payments related to the defined benefit plans are shown below. Payments (In millions) 2018 $ 0.8 2019 0.9 2020 1.0 2021 1.1 2022 1.2 2023-2027 11.6 Defined Contribution Plan Prior to the Separation, Air Products sponsored several defined contribution plans which covered all U.S. employees and certain non-U.S. employees. Versum received an allocation of the total cost of defined contributions from Air Products. Upon Separation, our employees’ balances were transferred to a new Versum defined contribution plan. The following table summarizes our defined contribution expense: 2017 2016 2015 (In millions) Defined contribution expense $ 11.0 $ 5.5 $ 4.5

Share Based Compensation Share

Share Based Compensation Share Based Compensation	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	16. 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, each holder of Air Products share-based compensation awards generally received an adjusted award denominated in Versum equity as follows: (a) Air Products stock options were converted into options to purchase Versum common stock, with the number and exercise price adjusted to maintain economic value; (b) Air Products time-based restricted stock units were converted to Versum time-based restricted stock units, with the number adjusted to maintain economic value; (c) Air Products performance shares in the form of market-based restricted stock units were converted to Versum market-based restricted stock units, with the number adjusted to maintain economic value; and (d) holders of Air Products restricted stock received one-half of a fully vested share of Versum common stock for every share of Air Products restricted stock held at the time of the Separation, as if such holder held fully vested Air Products common stock on the record date. 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. For the years ended September 30, 2017 , 2016 , and 2015 , share-based compensation expense of $8.3 million , $5.0 million , and $4.7 million , respectively, was included in the Annual Consolidated Financial Statements. In addition, 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 and we made fiscal 2017 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 September 30, 2017 , there were 3.3 million shares available for future grant under the Versum Long-Term Incentive Plan. Share-based compensation award cost recognized in the consolidated income statement is summarized below: Year Ended September 30, 2017 (In millions) Before-Tax Share-Based Compensation Award Cost $ 8.3 Income Tax Benefit 2.9 After-Tax Share-Based Compensation Award Cost $ 5.4 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: Year Ended September 30, 2017 (In millions) Restricted stock units $ 7.5 Stock options 0.2 Director awards 0.6 Before-Tax Share-Based Compensation Cost $ 8.3 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 one share 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, 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 generally vest on the date that the Versum 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, each restricted stock unit represents the right to receive one share 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, 2016 had an estimated grant-date fair value of $29.68 per unit for the performance-based restricted stock units and $28.37 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, 2016 used the following assumptions: (In percentages) Expected volatility 28.7 % Risk-free interest rate 1.4 % 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, 2016 — $ — Converted on October 1, 2016 0.5 22.85 Granted 0.7 25.30 Paid out (0.1 ) 15.55 Forfeited/adjustments — — Outstanding, September 30, 2017 1.1 $ 25.30 No cash payments were made for restricted stock units for the year ended September 30, 2017 . As of September 30, 2017 , there was $13.9 million of unrecognized compensation cost related to restricted stock units. The cost is expected to be recognized over a weighted average period of 2.5 years. The total fair value of restricted stock units paid out during the year ended September 30, 2017 , including shares vested in prior periods, was $ 1.7 million . 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 year ended September 30, 2017 , 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, 2016 — $ — Converted on October 1, 2016 0.5 18.37 Granted — — Exercised — — Forfeited — — Outstanding, September 30, 2017 0.5 $ 18.55 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, September 30, 2017 5.6 $ 9.6 Exercisable, September 30, 2017 5.6 9.3 The aggregate intrinsic value represents the amount by which our closing stock price of $38.82 as of September 30, 2017 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 year ended September 30, 2017 was $0.9 million . 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 September 30, 2017 , there was $0.1 million of unrecognized compensation cost related to non-vested stock options, which is expected to be recognized over a weighted average period of 0.3 years. Director Awards Under the Versum Long-Term Incentive Plan, non-employee directors each receive quarterly grants of our common stock with a quarterly grant date fair value of $25,000 . 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 year ended September 30, 2017 , $0.6 million in share-based compensation expense was recognized related to these awards.

Stock Holders Equity Stock Hold

Stock Holders Equity Stock Holders Equity	12 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	17. STOCKHOLDERS' EQUITY Accumulated Other Comprehensive Loss The table below summarizes changes in accumulated other comprehensive loss (AOCL), net of tax: 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 — (8.7 ) 3.7 (5.0 ) Net transfers from Air Products — 3.8 (6.2 ) (2.4 ) Amounts reclassified from AOCL — — 0.3 0.3 Net current period other comprehensive loss — (4.9 ) (2.2 ) (7.1 ) Other comprehensive loss attributable to non-controlling interest — 1.3 — 1.3 Balance, September 30, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 ) The table below summarizes the reclassifications out of accumulated other comprehensive loss and the affected line item on the consolidated income statements: Year Ended September 30, 2017 (In millions) Pension and Postretirement Benefits, net of tax (A) $ 0.3 (A) The components include actuarial loss amortization and are reflected in net periodic benefit cost. Refer to Note 15 , 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. In March 2017, the Company’s Board of Directors declared a cash dividend of $0.05 per share, totaling $5.4 million , which was paid on April 19, 2017 to shareholders of record as of April 5, 2017. Additionally, on July 27, 2017, the Company’s Board of Directors declared a second cash dividend of $0.05 per share totaling $5.4 million , which was paid on August 21, 2017 to shareholders of record as of August 7, 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

Earnings Per Share Earnings Per Share	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Share	18. EARNINGS PER SHARE The following table sets forth the computation of basic and diluted earnings per share: September 30, 2017 2016 2015 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 193.0 $ 212.0 $ 184.1 Denominator Weighted average number of common shares - Basic 108.7 108.7 108.7 Effect of dilutive securities Employee stock option and other award plans 0.7 — — Weighted average number of common shares - Diluted 109.4 108.7 108.7 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 1.78 $ 1.95 $ 1.69 Net Income Attributable to Versum - Diluted 1.76 1.95 1.69 The computation of basic and diluted earnings per common share is calculated assuming the number of shares of Versum common stock outstanding on October 1, 2016 had been outstanding at the beginning of each period presented. For periods prior to the Separation, it is assumed that there are no dilutive equity instruments as there were no equity awards in Versum outstanding prior to the Separation. See Note 1 , “ Basis of Presentation ” for further discussion of the Separation. For the year ended September 30, 2017 , no outstanding share-based awards were anti-dilutive.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	19. INCOME TAXES The following table summarizes the income of U.S. and foreign operations before taxes: Year Ended September 30, 2017 2016 2015 (In millions) Income Before Taxes United States $ 28.8 $ 61.6 $ 41.7 Foreign 223.9 217.1 181.2 Total $ 252.7 $ 278.7 $ 222.9 The following table shows the components of the provision for income taxes: Year Ended September 30, 2017 2016 2015 (In millions) Current Tax Provision Federal $ 2.4 $ — $ — State 0.6 0.6 0.5 Foreign 47.0 58.3 31.6 50.0 58.9 32.1 Deferred Tax Provision Federal 1.1 1.3 1.4 State 0.1 0.1 0.1 Foreign 1.6 (1.5 ) (1.9 ) 2.8 (0.1 ) (0.4 ) Income Tax Provision $ 52.8 $ 58.8 $ 31.7 Income tax expense (benefit) differs from the expected amounts based on the statutory U.S. federal tax rate for the years ended September 30, 2017 , 2016 and 2015 as follows: Year Ended September 30, 2017 2016 2015 (In millions) U.S. federal tax $ 88.4 $ 97.5 $ 78.0 State taxes, net of federal benefit 0.5 2.2 1.3 Foreign tax differentials (34.7 ) (30.7 ) (37.4 ) U.S. taxes on foreign earnings (0.3 ) 4.7 (2.0 ) Other credit and incentives (0.8 ) (0.8 ) (0.7 ) Valuation allowance 0.9 (19.2 ) (6.2 ) Other (1.2 ) 5.1 (1.3 ) Income Tax Expense (Benefit) $ 52.8 $ 58.8 $ 31.7 Foreign tax differentials represent the differences between foreign earnings subject to foreign tax rates lower than the U.S. federal statutory tax rate of 35.0% . Foreign earnings are subject to local country tax rates that are generally below the 35.0% U.S. federal statutory rate. As a result, our effective non-U.S. tax rate is typically lower than the U.S. statutory rate. If foreign pre-tax earnings increase relative to U.S. pre-tax earnings, this rate difference could increase. The primary jurisdictions in which we earn pre-tax earnings subject to lower foreign taxes than the U.S. statutory rate include South Korea, China, Taiwan, and Singapore. As substantially all of our undistributed earnings are in countries with a statutory tax rate of 17% or higher, we do not generate a disproportionate amount of taxable income in countries with very low tax rates. U.S. taxes on foreign earnings include the cost of foreign withholding taxes imposed on dividends paid to U.S. shareholders. We have certain foreign subsidiaries that were granted seven-year tax holidays, the majority of which expired during the year ending September 30, 2017. The tax benefit of the holidays is reduced by 50% in the last two years of the holiday period. The net benefit of the tax holidays was $8.0 million , $7.1 million , and $9.6 million in 2017 , 2016 and 2015 , respectively. We maintained a valuation allowance in 2015 and 2016 against U.S. deferred tax accounts resulting primarily from restructuring charges taken in prior periods, as we determined that it was more likely than not that U.S. deferred tax assets would not be realized. These deferred tax assets related primarily to net operating loss and tax credit carryforwards derived from the stand-alone basis calculation. The valuation allowance benefits in 2015 and 2016 shown in the table above relate to the utilization of federal net operating losses as a result of favorable operations. These net operating losses and tax credit carryforwards were utilized against Air Products’ income and are not available as future deductions on Versum tax returns. The current period effective tax rate, therefore, includes no valuation allowance benefit related to U.S. deferred tax assets. The valuation allowance cost for 2017 relates to certain foreign tax credits accrued outside the U.S. The significant components of deferred tax assets and liabilities are as follows: September 30, 2017 2016 (In millions) Gross Deferred Tax Assets Tax loss carryforwards $ 0.5 $ 13.2 Tax credit carryforwards 0.9 64.2 Retirement benefits and compensation accruals 10.9 7.6 Reserves and accruals 1.6 8.4 Other 1.5 3.3 Valuation allowance (0.9 ) (55.6 ) Deferred Tax Assets 14.5 41.1 Gross Deferred Tax Liabilities Intangible assets 9.1 41.0 Plant and equipment 22.9 22.2 Unremitted earnings of foreign entities 0.7 2.3 Partnership investments 0.8 1.3 Other 0.2 6.3 Deferred Tax Liabilities 33.7 73.1 Net Deferred Income Tax Liability $ 19.2 $ 32.0 Deferred tax assets and liabilities are included within the Annual Consolidated Financial Statements as follows: September 30, 2017 2016 (In millions) Other non-current assets $ 18.1 $ 10.8 Deferred tax liabilities 37.3 42.8 Net Deferred Income Tax Liability $ 19.2 $ 32.0 As discussed in Note 1, the Separation of Versum from Air Products was completed on October 1, 2016. In connection with the Separation and as a result of the change from the separate return method under the carve-out financial statements, Versum adjusted certain current and deferred tax accounts, including a net decrease in deferred tax liabilities of approximately $17.5 million and a net increase in tax payable of approximately $13.0 million . The federal and state tax carryforwards and credits resulting from the stand-alone basis calculation were utilized against Air Products’ income and are not available as future deductions on tax returns. As such they were not transferred as part of the Separation from Air Products, and the related deferred tax assets and valuation allowance were removed. The decrease in net deferred tax liabilities was related primarily to deferred tax assets created in the Separation that were not recorded in the carve-out financial statements. The increase in tax payable was related primarily to taxes payable in entities shared with Air Products prior to the Separation, the liability for which was not included in the carve-out financial statements. The Company paid $42.9 million of cash income taxes during the fiscal year ended September 30, 2017. We have no federal foreign tax credit and research credit carryforwards as of September 30, 2017. Gross foreign loss carryforwards as of September 30, 2017 were $1.5 million , and expire in 2026. The valuation allowance as of September 30, 2017 is related to the tax benefit of foreign tax credits accrued in jurisdictions outside the U.S. The $54.7 million decrease in the valuation allowance was primarily due to change from the separate return method under the carve-out financial statements. As of September 30, 2017 , we believed it would be more likely than not that future earnings and reversal of deferred tax liabilities would be sufficient to utilize the deferred tax asset reflected on the financial statements, net of existing valuation allowance. We record 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. These cumulative undistributed earnings that were considered to be indefinitely reinvested in foreign subsidiaries and corporate joint ventures is estimated to be $1,070.8 million as of September 30, 2017 . An estimated $196.2 million in U.S. income and foreign withholding taxes would be due if these earnings were remitted as dividends. A reconciliation of the beginning and ending amount of the unrecognized tax benefits is as follows: Year Ended September 30, (In millions) 2017 2016 2015 Unrecognized Tax Benefits Balance at beginning of year $ 12.9 $ 10.3 $ 16.0 Additions for tax positions for the current year 2.1 1.9 1.6 Additions for tax positions of prior years 5.2 1.0 0.1 Reductions for tax positions of prior years (0.2 ) (0.1 ) (4.7 ) Statute of limitations expiration (0.1 ) (0.2 ) (2.7 ) Balance at End of Year $ 19.9 $ 12.9 $ 10.3 At September 30, 2017 and 2016 , we had $19.9 million and $12.9 million of unrecognized tax benefits of which $19.9 million and $12.6 million , respectively, would impact the tax rate, if recognized. Interest and penalties related to unrecognized tax benefits are recorded as a component of income tax expense. We are currently under examination in a number of tax jurisdictions, some of which may be resolved in the next twelve months. As a result, it is reasonably possible that a change in the unrecognized tax benefits may occur during the next twelve months. However, quantification of an estimated range cannot be made at this time. We generally remain subject to examination in the following major tax jurisdictions for the years indicated below: Open Tax Years Major Tax Jurisdiction United States 2017 China 2007-2017 South Korea 2010-2017 Taiwan 2012-2017

Supplemental Information

Supplemental Information	12 Months Ended
	Sep. 30, 2017
Supplemental Balance Sheet Information [Abstract]
Supplemental Information	20. SUPPLEMENTAL INFORMATION September 30, (In millions) 2017 2016 Payables and Accrued Liabilities Trade creditors $ 56.0 $ 41.6 Customer advances 5.3 4.0 Accrued payroll and employee benefits 41.2 33.9 Other costs associated with business separation, restructuring and cost reduction actions 7.9 0.6 Derivatives 1.5 — Other 8.9 5.7 $ 120.8 $ 85.8

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	21. 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. Environmental and Regulatory Proceedings From time to time, Versum may be involved in proceedings, investigations, and audits involving governmental authorities in connection with environmental, health, safety, competition, and tax matters. In addition, pursuant to the Separation Agreement, Versum is liable to Air Products for proceedings by the Environmental Protection Agency under the Comprehensive Environmental Response, Compensation, and Liability Act, the federal Superfund law (“CERCLA”); the Resource Conservation and Recovery Act (“RCRA”); and similar state and foreign environmental laws relating to current or former Electronic Materials business sites, and third-party waste disposal facilities used by the Electronic Materials business, that have been designated for investigation or remediation. Versum may be liable for any unknown environmental liabilities related to legacy businesses and sites formerly owned and operated by Air Products related to its former electronics businesses. Versum does not currently believe that there are any environmental or regulatory matters, individually or in the aggregate, that are reasonably possible to have a material impact on our financial condition, results of operations, or cash flows. Any future charges related to the costs of litigation, environmental, or regulatory proceedings for fines, settlements or damages related to any such matters could have a material impact on our results of operations or cash flows in the period incurred. 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. Unconditional Purchase Obligations We have unconditional purchase obligations of approximately $30.3 million for plant and equipment purchases as well as R&D facility enhancements. Otherwise, there are no material obligations.

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment and Geographic Information	22. SEGMENT AND GEOGRAPHIC 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. 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 majority of our sales to the semiconductor industry are to large scale multinational companies. Delivery Systems and Services The Delivery Systems and Services 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. 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. Corporate assets primarily include cash and deferred tax assets. Customers For the fiscal years ended September 30, 2017 , 2016 , and 2015 , three customers accounted for 10% or more of combined sales from both the Materials and Delivery Systems and Services segments. In 2017 , these customers accounted for 22% , 13% and 12% of our combined sales. In 2016 , these customers accounted for 21% , 13% and 13% of our combined sales. In 2015 , these customers accounted for 21% , 13% , and 11% of our combined sales. No other customer accounted for more than 10% of combined sales in any period. Products For the fiscal years ended September 30, 2017 and 2016 , a Materials segment product accounted for 10% or more of combined sales from both the Materials and Delivery Systems and Services segments. For the fiscal years ended September 30, 2017 and 2016 , this product accounted for 11% and 12% of our combined sales, respectively. Accounting Policies The accounting policies of the segments are the same as those described in Note 2 , Major Accounting Policies. We evaluate the performance of segments based upon reported segment operating income. Intersegment sales are not material and are recorded at selling prices that approximate market prices. Segment As of and for the year ended September 30, 2017 2016 2015 (In millions) Sales Materials $ 829.7 $ 756.7 $ 743.4 Delivery Systems and Services 293.6 213.4 265.9 Corporate 3.6 — — Combined Total $ 1,126.9 $ 970.1 $ 1,009.3 Operating Income (Loss) Materials $ 274.4 $ 252.3 $ 213.7 Delivery Systems and Services 71.7 50.8 49.1 Corporate (20.5 ) (23.3 ) (19.2 ) Segment Total 325.6 279.8 243.6 Business separation, restructuring and cost reduction actions (25.5 ) (0.9 ) (21.6 ) Combined Total $ 300.1 $ 278.9 $ 222.0 Depreciation and Amortization Materials $ 43.1 $ 44.4 $ 48.1 Delivery Systems and Services 1.4 2.1 8.3 Corporate 1.5 0.4 0.5 Combined Total $ 46.0 $ 46.9 $ 56.9 Equity Affiliates’ Income Materials $ — $ 0.2 $ 1.0 Combined Total $ — $ 0.2 $ 1.0 Total Assets Materials $ 773.8 $ 733.4 $ 754.8 Delivery Systems and Services 110.9 104.0 92.7 Corporate 362.1 206.4 39.9 Combined Total $ 1,246.8 $ 1,043.8 $ 887.4 Investment in Net Assets of and Advances to Equity Affiliates Materials $ — $ — $ 12.5 Combined Total $ — $ — $ 12.5 Expenditures for Long-Lived Assets Materials $ 45.7 $ 34.4 $ 21.2 Delivery Systems and Services 1.7 0.7 0.8 Corporate 16.6 0.7 0.1 Combined Total $ 64.0 $ 35.8 $ 22.1 Sales by Product Group Year Ended September 30, 2017 2016 2015 (In millions) Process Materials $ 401.8 $ 387.4 $ 387.3 Advanced Materials 427.9 369.3 356.1 Equipment and Installations 235.4 150.8 208.3 Site Services 58.2 62.6 57.6 Corporate 3.6 — — Total $ 1,126.9 $ 970.1 $ 1,009.3 Geographic Information Year Ended September 30, 2017 2016 2015 (In millions) Sales to External Customers United States $ 375.7 $ 349.4 $ 361.3 Taiwan 242.8 230.8 236.3 South Korea 304.1 217.2 220.3 China 64.9 53.8 70.9 Europe 63.1 57.8 69.2 Asia, excluding China, Taiwan, and South Korea 76.3 61.1 51.3 Total $ 1,126.9 $ 970.1 $ 1,009.3 September 30, 2017 2016 2015 (In millions) Long-Lived Assets (A) United States $ 170.3 $ 138.3 $ 139.9 South Korea 112.2 112.2 105.0 Taiwan 38.2 36.8 39.7 Asia, excluding Taiwan and South Korea 9.2 9.0 16.4 Europe 0.4 0.2 0.1 Total $ 330.3 $ 296.5 $ 301.1 (A) Long-lived assets include plant and equipment, net. Geographic information is based on country of origin. Included in United States revenues are export sales to third-party customers of $68.7 million in 2017 , $75.8 million in 2016 , and $54.2 million in 2015 .

Acquisition Acquisition

Acquisition Acquisition	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Acquisition	23. ACQUISITION On August 1, 2017, the Company completed the acquisition of 100% of Dynaloy, LLC (“Dynaloy”) from Eastman Chemical Co. Dynaloy is a supplier of formulated cleaning solutions for the semiconductor and specialty manufacturing industries. The purchase price of approximately $13 million was paid in cash from our available cash balance. The acquisition of Dynaloy does not constitute a material business combination. The Company has accounted for the acquisition as a business combination in accordance with ASC 805, Business Combinations ("ASC 805"), and has included Dynaloy within the Materials reportable segment. In applying the provisions of ASC 805 and determining that Dynaloy represents a business, the Company elected to early adopt and apply ASU 2017-01 (refer to Note 1). Under ASU 2017-01, the Company first assessed whether all of the fair value of the acquired Dynaloy gross assets is concentrated in a single identifiable asset or group of identifiable assets. If that concentration existed, Dynaloy would not be considered a business. The Company concluded that there was not such a concentration, as the fair value of the acquired gross assets is distributed between various intangible and tangible assets. The Company has allocated the acquisition purchase price to the tangible net assets and identifiable intangible assets acquired based on their estimated fair values at the acquisition date and recorded the excess as goodwill. The valuation of the assets and liabilities acquired was based on the information that was available as of the acquisition date and the expectations and assumptions that have been deemed reasonable by the Company’s management. In performing these valuations, the Company used discounted cash flows and other factors as the best evidence of fair value. The key underlying assumptions of the discounted cash flows were projected revenues and royalty rates. The Company has recognized $5.0 million of goodwill, which is attributable to the revenue growth and operating synergies that Versum expects to realize from this acquisition. The Company’s estimates and assumptions used in determining the estimated fair values of the net assets acquired are subject to change within the measurement period (up to one year from the acquisition date) as a result of additional information obtained with regards to facts and circumstances that existed as of the acquisition date. The following table presents the aggregate purchase price allocation, as of September 30, 2017 . Net Assets Acquired (In millions) Accounts receivable $ 1.0 Other current assets 0.1 Inventories 1.4 Properties and Equipment, net 2.4 Goodwill 5.0 Intangible assets 3.7 Other current liabilities (0.4 ) Net assets acquired $ 13.2 The table below presents the intangible assets acquired as part of the acquisition of Dynaloy and the periods over which they will be amortized on a straight line basis. Amount Weighted Average Amortization Period (In millions, except years) Technology $ 2.8 7 Trademarks 0.9 5 Total $ 3.7

Subsequent Events

Subsequent Events	12 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	24. SUBSEQUENT EVENTS Cash Dividend On October 31, 2017, the Company’s Board of Directors declared a quarterly cash dividend of $0.05 per share, to be paid on November 27, 2017 to shareholders of record as of November 13, 2017.

Summary By Quarter (Unaudited)

Summary By Quarter (Unaudited)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Summary By Quarter (Unaudited)	25. SUMMARY BY QUARTER (UNAUDITED) These tables summarize the unaudited results of operations for each quarter of fiscal 2017 and 2016 : For the Quarter Ended December 31, 2016 March 31, 2017 June 30, 2017 September 30, 2017 Total (In millions) Sales $ 270.8 $ 270.8 $ 290.8 $ 294.5 $ 1,126.9 Cost of sales 150.9 154.5 159.6 171.9 636.9 Selling and administrative 30.2 29.5 34.5 31.5 125.7 Research and development 10.3 10.9 11.9 12.0 45.1 Business separation, restructuring and cost reduction actions 3.2 6.1 6.0 10.2 25.5 Other (income) expense, net (2.9 ) (0.1 ) (2.2 ) (1.2 ) (6.4 ) Operating Income 79.1 69.9 81.0 70.1 300.1 Equity affiliates’ income — — — — — Interest expense 11.5 11.6 11.9 12.4 47.4 Income Before Taxes 67.6 58.3 69.1 57.7 252.7 Income tax provision 15.3 11.5 14.4 11.6 52.8 Net Income 52.3 46.8 54.7 46.1 199.9 Less: Net Income Attributable to Non-controlling Interests 1.5 1.9 2.0 1.5 6.9 Net Income Attributable to Versum $ 50.8 $ 44.9 $ 52.7 $ 44.6 $ 193.0 For the Quarter Ended December 31, 2015 March 31, 2016 June 30, 2016 September 30, 2016 Total (In millions) Sales $ 245.5 $ 233.5 $ 242.7 $ 248.4 $ 970.1 Cost of sales 132.4 132.5 135.9 138.7 539.5 Selling and administrative 23.6 25.7 27.3 33.2 109.8 Research and development 10.9 10.2 11.3 11.5 43.9 Business separation, restructuring and cost reduction actions (0.9 ) (1.8 ) 1.1 2.5 0.9 Other (income) expense, net (1.1 ) (1.0 ) (0.3 ) (0.5 ) (2.9 ) Operating Income 80.6 67.9 67.4 63.0 278.9 Equity affiliates’ income 0.2 — — — 0.2 Interest expense — — — 0.4 0.4 Income Before Taxes 80.8 67.9 67.4 62.6 278.7 Income tax provision 13.4 12.2 17.6 15.6 58.8 Net Income 67.4 55.7 49.8 47.0 219.9 Less: Net Income Attributable to Non-controlling Interests 2.2 1.9 2.0 1.8 7.9 Net Income Attributable to Versum $ 65.2 $ 53.8 $ 47.8 $ 45.2 $ 212.0

Schedule II-Valuation and Quali

Schedule II-Valuation and Qualifying Accounts	12 Months Ended
	Sep. 30, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II-Valuation and Qualifying Accounts	SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS For the Years Ended September 30, 2017 , 2016 , and 2015 Balance at Change Other (A) Balance at (In millions) Year Ended September 30, 2017 Allowance for doubtful accounts $ 0.8 0.2 — $ 1.0 Allowance for deferred tax assets $ 55.6 0.9 (55.6 ) $ 0.9 Year Ended September 30, 2016 Allowance for doubtful accounts $ 0.8 — — $ 0.8 Allowance for deferred tax assets $ 77.7 (20.8 ) (1.3 ) $ 55.6 Year Ended September 30, 2015 Allowance for doubtful accounts $ 2.2 0.1 (1.5 ) $ 0.8 Allowance for deferred tax assets $ 83.3 (4.9 ) (0.7 ) $ 77.7 (A) For 2017, Other Changes primarily includes adjustments related to the Separation. For 2016 and 2015, Other Changes primarily includes write-offs of uncollectible trade receivable accounts and the impact of foreign currency translation adjustments.

Major Accounting Policies (Poli

Major Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	he accompanying Annual Consolidated Financial Statements of Versum, were prepared on a stand-alone basis and were derived from Air Products’ consolidated financial statements and accounting records where Versum was a division of Air Products. For all periods presented, the Annual Consolidated Financial Statements were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Versum. All significant intercompany transactions and balances have been eliminated in the preparation of the accompanying Annual Consolidated Financial Statements. Prior to the Separation, transactions between Versum and Air Products were reflected in the annual consolidated balance sheets as “Air Products’ net investment” and in the annual consolidated statements of cash flows as a financing activity in “Net transfers (to) from Air Products.”
Allocation of Shared Costs	Air Products provided us with centrally managed services and corporate functions. Accordingly, certain shared costs including but not limited to administrative expenses for information technology, general services, human resources, legal, accounting and other services, had been allocated to us and were reflected as expenses in the Annual Consolidated Financial Statements. Expenses had been allocated on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed costs, revenue, operating income or headcount. We consider the expense allocation methodology and results to be reasonable and consistently applied for all periods presented prior to the Separation.
Estimates and Assumptions	Estimates and Assumptions The preparation of the Annual Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the Annual Consolidated Financial Statements and accompanying notes, including allocations of costs during the reporting period. Management’s estimates are based on historical experience, facts and circumstances available at the time, and various other assumptions that are believed to be reasonable. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognition Revenue from product sales is recognized as risk and title to the product transfer to the customer (which generally occurs at the time shipment is made), the sales price is fixed or determinable, and collectability is reasonably assured. Sales returns and allowances are generally not a business practice in the industry. We use both the completed contract and percentage-of-completion methods to record revenue from equipment sale contracts. The completed contract method is used in circumstances in which financial position and results of operations are not materially different from those resulting from use of the percentage-of-completion method, e.g., certain short-term contracts. We use the percentage-of-completion method when we can make reasonably dependable estimates of progress toward completion and performance is expected. Under the percentage-of-completion method, revenue from the sale of major equipment is recognized primarily based on costs incurred to date compared with total estimated costs. Under the completed contract method, revenue and cost is recognized when the equipment is completed and transferred to the customer. Changes to estimated labor hours under the percentage-of-completion method or anticipated losses under either method, if any, are recognized in the period determined. Revenue from on-site services are generally fixed monthly fee arrangements for which we recognize revenue as the services are performed. Amounts billed for shipping and handling fees are classified as sales in the consolidated income statements. Amounts billed for sales and use taxes, value-added taxes, and certain excise and other specific transactional taxes imposed on revenue-producing transactions are presented on a net basis and excluded from sales in the consolidated income statements. We record a liability until remitted to the respective taxing authority.
Cost of Sales	Cost of Sales Cost of sales predominantly represents the cost of tangible products sold. These costs include labor, raw materials, depreciation, production supplies, and materials packaging costs. Costs incurred for shipping and handling are also included in cost of sales.
Depreciation	Depreciation Depreciation is recorded using the straight-line method, which deducts equal amounts of the cost of each asset from earnings every year over its expected economic useful life.
Selling and Administrative	Selling and Administrative The principal components of selling and administrative expenses are compensation, advertising, and promotional costs.
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development expenses include employee costs, materials, contract services, research agreements, and other external spending related to the discovery and development of new products, enhancement of existing products and regulatory approval of new and existing products.
Postemployment Benefits	Post-employment Benefits We provide termination benefits to employees as part of ongoing benefit arrangements and record a liability for termination benefits when probable and estimable. These criteria are met when management, with the appropriate level of authority, approves and commits to its plan of action for termination; the plan identifies the employees to be terminated and their related benefits; and the plan is to be completed within one year. We typically do not provide one-time benefit arrangements of significance.
Fair Value Measurements	Fair Value Measurements We are required to measure certain assets and liabilities at fair value, either upon initial measurement or for subsequent accounting or reporting. For example, fair value is used in the initial measurement of net assets acquired in a business combination; on a recurring basis in the measurement of derivative financial instruments; and on a nonrecurring basis when long-lived assets are written down to fair value when held for sale or determined to be impaired.
Financial Instruments	Financial Instruments We address certain financial exposures through a controlled program of risk management that includes the use of derivative financial instruments. If the circumstances qualify and we designate hedge accounting, the hedging relationship between the underlying financial exposures and the related hedging instrument would be documented on the date the derivative is entered into with the counterparty. Our program currently includes the use of forward exchange contracts to hedge intercompany loans denominated in a foreign currency. We have not designated hedge accounting for any of the forward exchange contracts.
Foreign Currency	Foreign Currency Since we do business in many foreign countries, fluctuations in currency exchange rates affect our financial position and results of operations. In certain of our foreign operations, the local currency is considered the functional currency. These foreign subsidiaries translate their assets and liabilities into U.S. dollars at current exchange rates in effect at the end of the fiscal period. The gains or losses that result from this process are shown as translation adjustments in accumulated other comprehensive income (loss) in the stockholders’ equity section of the annual consolidated balance sheets. The revenue and expense accounts of these foreign subsidiaries are translated into U.S. dollars at the average exchange rates that prevail during the period. Therefore, the U.S. dollar value of these items on the income statement fluctuates from period to period, depending on the value of the dollar against foreign currencies. Some transactions are made in currencies different from an entity’s functional currency. Gains and losses from these foreign currency transactions are generally included in other income (expense), net on our consolidated income statements as they occur.
Litigation	Litigation Accruals for litigation are made when the information available indicates that it is probable that a liability has been incurred and the amount can be reasonably estimated. When only a range of possible loss can be established, the most probable amount in the range is accrued. If no amount within this range is a better estimate than any other amount within the range, the minimum amount in the range is accrued. The accrual for a litigation loss contingency includes estimates of potential damages and other directly related costs expected to be incurred. Litigation liabilities and expenditures included in the Annual Consolidated Financial Statements were not material for the periods presented.
Share-Based Compensation	Share-Based Compensation Prior to the Separation, our employees participated in Air Products’ share-based compensation plans, which included stock options, deferred stock units, and restricted stock. Prior to the Separation, the Annual Consolidated Financial Statements included share-based compensation expense associated with our employees and Air Products’ costs that had been allocated to us based on awards and terms previously granted. 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. The grant-date fair value of awards is expensed over the vesting period during which employees perform related services. Expense recognition is accelerated for retirement-eligible individuals who would meet the requirements for vesting of awards upon their retirement. The Black Scholes model is utilized to value new stock option awards. The grant date fair value of the deferred stock units tied to a market condition is estimated using a Monte Carlo simulation model for new awards.
Income Taxes	Income Taxes For the fiscal years ended September 30, 2016 and 2015, certain of our operations included in our Annual Consolidated Financial Statements were divisions of legal entities included in Air Products consolidated U.S. federal and state income tax returns, or tax returns of non-U.S. subsidiaries of Air Products. The provision for income taxes and related annual consolidated balance sheet accounts of such entities, for such periods, have been prepared and presented in the Annual Consolidated Financial Statements based on a stand-alone basis separate from Air Products. Differences between our separate return income tax provision and cash flows attributable to income taxes for operations that were divisions of legal entities have been recognized as capital contributions from, or dividends to, Air Products, within Air Products’ net investment. As a stand-alone entity, our deferred taxes and effective tax rate differ from those in historical periods. We account for income taxes under the liability method. Under this method, deferred tax assets and liabilities are recognized for the tax effects of temporary differences between the financial reporting and tax bases of assets and liabilities measured using enacted tax rates. The cumulative impact of a change in tax rates or regulations is included in income tax expense in the period that includes the enactment date. A tax benefit for an uncertain tax position is recognized when it is more likely than not that the position will be sustained upon examination based on its technical merits. This position is measured as the largest amount of tax benefit that is greater than 50% likely of being realized. Interest and penalties related to unrecognized tax benefits are recognized as a component of income tax expense. For the fiscal years ended September 30, 2016 and 2015, the majority of the accrued U.S. federal, state, and foreign income tax balances were treated as settled with Air Products as of the end of each year. Therefore, they are included in Air Products’ net investment in the Annual Consolidated Financial Statements, for such periods.
Non-controlling Interests	Non-controlling Interests We consolidate investments that we control but do not wholly own. The Annual Consolidated Financial Statements include all assets, liabilities, revenues, and expenses of our joint venture in Taiwan for which we have a 74% ownership interest during the periods presented in the Annual Consolidated Financial Statements. The ownership interests held by third party non-controlling partners are presented as non-controlling interests in our annual consolidated balance sheets. Any net income or loss attributed to the non-controlling partners is presented as such in the consolidated income statements. The activity for non-controlling interests for the years ended September 30, 2017 , 2016 and 2015 is presented in the annual consolidated statements of stockholders’ equity.
Cash and Cash Items	Cash and Cash Items Cash and cash items generally include cash, time deposits, and certificates of deposit acquired with an original maturity of three months or less for our foreign entities. Prior to the Separation, cash was managed centrally at Air Products and most cash generated by our business was remitted to Air Products. Such centralized cash management transactions relating to our business were reflected through Air Products’ net investment. Accordingly, none of the centrally managed cash at the Air Products’ corporate level had been reflected in our Annual Consolidated Financial Statements.
Restricted Cash	Restricted Cash Restricted cash consists of cash restricted for payment to Air Products made subsequent to the Separation.
Trade Receivables, net	Trade Receivables, net Trade receivables comprise amounts owed to us through our operating activities and are presented net of allowances for doubtful accounts. The allowances for doubtful accounts represent estimated uncollectible receivables associated with potential customer defaults on contractual obligations. A provision for customer defaults is made on a general formula basis when it is determined that the risk of some default is probable and estimable but cannot yet be associated with specific customers. The assessment of the likelihood of customer defaults is based on various factors, including the length of time the receivables are past due, historical experience, and existing economic conditions. The allowance also includes amounts for certain customers where a risk of default has been specifically identified, considering factors such as the financial condition of the customer and customer disputes over contractual terms and conditions.
Inventories	Inventories Inventories are stated at the lower of cost or market. We write down our inventories for estimated obsolescence or unmarketable inventory based upon assumptions about future demand and market conditions. We utilize the last-in, first-out (“LIFO”) method for determining the cost of inventories in the United States. Inventories outside of the United States are accounted for on the first-in, first-out (“FIFO”) method, as the LIFO method is not generally permitted in the foreign jurisdictions we operate.
Equity Investments	Equity Investments The equity method of accounting is used when we exercise significant influence but do not have operating control, generally assumed to be 20% to 50% ownership. Under the equity method, original investments are recorded at cost and adjusted by our share of undistributed earnings or losses of these companies. Equity investments are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the investment may not be recoverable. The Annual Consolidated Financial Statements include our investment in and proportionate share of the income from our 20% owned equity affiliate, Daido Air Products Electronics, Inc. During the first quarter of 2016, we sold our investment in this affiliate. Refer to Note 6 , “ Sale of Equity Affiliate ”, for additional information.
Plant and Equipment	Plant and Equipment Plant and equipment is stated at cost less accumulated depreciation. Construction costs, labor, and applicable overhead related to installations are capitalized. Expenditures for additions and improvements that extend the lives or increase the capacity of plant assets are capitalized. The costs of maintenance and repairs of plant and equipment are charged to expense as incurred. Fully depreciated assets are retained in the gross plant and equipment and accumulated depreciation accounts until they are removed from service. In the case of disposals, assets and related depreciation are removed from the accounts, and the net amounts, less proceeds from disposal, are included in income.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are grouped for impairment testing at the lowest level for which there are identifiable cash flows that are largely independent of the cash flows of other assets and liabilities and are evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable. We assess recoverability by comparing the carrying amount of the asset group to estimated undiscounted future cash flows expected to be generated by the asset group. If an asset group is considered impaired, the impairment loss to be recognized is measured as the amount by which the asset group’s carrying amount exceeds its fair value. Long-lived assets held for sale are reported at the lower of carrying amount or fair value less cost to sell.
Goodwill	Goodwill The purchase price is allocated to the assets acquired and liabilities assumed based on their estimated fair market values. Any excess purchase price over the fair market value of the net assets acquired, including identified intangibles, is recorded as goodwill. Preliminary purchase price allocations are made at the date of acquisition and finalized when information needed to affirm underlying estimates is obtained, within a maximum allocation period of one year. Goodwill is subject to impairment testing at least annually. In addition, goodwill is tested more frequently if a change in circumstances or the occurrence of events indicates that potential impairment exists.
Intangible Assets	Intangible Assets Intangible assets with determinable lives primarily consist of customer relationships and purchased patents and technology. The cost of intangible assets with determinable lives is amortized on a straight-line basis over the estimated period of economic benefit. Amortizable lives are adjusted whenever there is a change in the estimated period of economic benefit. No residual value is estimated for intangible assets.
Retirement Benefits	Retirement Benefits For periods prior to October 1, 2016, Air Products sponsored defined benefit pension plans, defined contribution plans, and other post-employment benefit plans that are shared amongst its businesses. Prior to the Separation on October 1, 2016, participation of our employees in these plans was reflected in the Annual Consolidated Financial Statements as though Versum participated in a multi-employer plan with Air Products. A proportionate share of cost was reflected in these Annual Consolidated Financial Statements, primarily within selling and administrative expenses.
Air Products' Net Investment	Air Products’ Net Investment Prior to the Separation, Air Products’ net investment in our business was presented as “Air Products’ net investment” in lieu of stockholders’ equity, as a stand-alone legal and capital structure did not exist for the historical periods presented.
Earnings Per Share	Earnings Per Share Prior to the Separation, Versum earnings per share for 2016 and 2015 were calculated using the shares that were distributed to Air Products stockholders immediately following the Separation. For periods prior to the Separation it is assumed that there are no dilutive equity instruments as there were no equity awards in Versum outstanding prior to the Separation.
New Accounting Guidance	Accounting Guidance Implemented Share-Based Compensation In March 2016, the Financial Accounting Standards Board (“FASB”) issued an update to simplify the accounting for employee share-based payments, including the income tax impacts, the classification on the statement of cash flows, and forfeitures. The amendments are effective for fiscal year 2018, with early adoption permitted. As of the first quarter of fiscal year 2017, we have adopted this guidance. Share-Based Compensation In May 2017, the FASB issued guidance which amends the scope of modification accounting for share-based payment arrangements. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. The Company adopted the standard effective October 1, 2017. The adoption is not expected to have a material impact on the Annual Consolidated Financial Statements. Going Concern In August 2014, the FASB issued guidance regarding management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern within one year of the issuance of the financial statements. If substantial doubt exists, additional disclosures would be required. The Company adopted the standard effective October 1, 2017. This guidance did not have a significant impact on our Annual 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 interim and annual reporting periods beginning after December 15, 2017. The components of the net (benefit) cost are shown in Note 15 , “ 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 Annual Consolidated Financial Statements. Goodwill Impairment In January 2017, the 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, 2021, 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 will adopt the standard effective October 1, 2017. The adoption is not expected to have a material impact on the Annual 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 Annual 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 Annual Consolidated Financial Statements. Measurement of Inventory In July 2015, the FASB issued guidance to simplify the measurement of inventory recorded using either the 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 LIFO is not impacted. The guidance is effective for us beginning in fiscal year 2018 and will be applied prospectively, with early adoption permitted. This guidance is not expected to have a significant impact on our Annual 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 and vehicles that are currently accounted for as operating leases as discussed in Note 12 , “ 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 Annual 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 Annual Consolidated Financial Statements.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Schedule of Total Costs Allocated	Total costs allocated to us in the consolidated income statements are summarized below: Year Ended September 30, 2017 2016 2015 (In millions) Cost of sales $ — $ 2.8 $ 3.6 Selling and administrative — 16.8 17.8 Research and development — 1.0 1.4 Business restructuring and cost reduction actions — 0.7 3.5 Total Allocated Costs $ — $ 21.3 $ 26.3

Business Separation, Restruct36

Business Separation, Restructuring, and Cost Reduction Actions (Tables)	12 Months Ended
	Sep. 30, 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 September 30, 2017 : Severance and Other Benefits Asset Actions/Other Total (In millions) September 30, 2014 $ 0.9 $ — $ 0.9 2015 Charge 14.4 7.2 21.6 Cash payments (A) (11.2 ) — (11.2 ) Non-cash expenses — (7.2 ) (7.2 ) September 30, 2015 $ 4.1 $ — $ 4.1 2016 Charge 2.5 (3.2 ) (0.7 ) Cash (payments) receipts (A) (6.0 ) 4.2 (1.8 ) Non-cash expenses — (1.0 ) (1.0 ) September 30, 2016 $ 0.6 $ — $ 0.6 2017 Charge 4.7 — 4.7 Cash payments (1.1 ) — (1.1 ) Non-cash expenses — — — September 30, 2017 $ 4.2 $ — $ 4.2 (A) Cash payments include an allocation of severance and other benefits of Air Products’ employees within its Corporate and other segment which were paid by Air Products.

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Sep. 30, 2017
Inventory Disclosure [Abstract]
Components of Inventories	The components of inventories are as follows: September 30, 2017 2016 (In millions) Inventories at FIFO cost Finished goods $ 87.6 $ 94.0 Work in process 20.3 12.3 Raw materials, supplies and other 52.5 29.4 160.4 135.7 Less: Excess of FIFO cost over LIFO cost (8.8 ) (8.3 ) Inventories $ 151.6 $ 127.4

Plant and Equipment, Net (Table

Plant and Equipment, Net (Tables)	12 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Major Classes of Plant and Equipment	The major classes of plant and equipment are as follows: September 30, Useful Life in years 2017 2016 (In millions, except useful life) Land $ 21.8 $ 21.9 Buildings 30 149.3 147.1 Machinery and Equipment Production facilities 10 to 15 479.9 433.6 Distribution and other (A) 5 to 25 252.1 255.9 Total machinery and equipment 732.0 689.5 Construction in progress 52.1 26.2 Plant and equipment, at cost 955.2 884.7 Less: accumulated depreciation 624.9 588.2 Plant and equipment, net $ 330.3 $ 296.5 (A) The depreciable lives for various types of distribution equipment are 10 to 25 years for cylinders, depending on the nature and properties of the product, and generally 20 years for other distribution equipment such as tanks and trailers.

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Sep. 30, 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 at September 30, 2015 $ 150.6 $ 16.4 $ 167.0 Currency translation adjustment 12.0 1.1 13.1 Balance at September 30, 2016 $ 162.6 $ 17.5 $ 180.1 Acquisition (Note 23) 5.0 — 5.0 Currency translation adjustment (2.3 ) (0.2 ) (2.5 ) Balance at September 30, 2017 $ 165.3 $ 17.3 $ 182.6

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Acquired Intangible Assets	The table below provides details of acquired intangible assets: September 30, 2017 September 30, 2016 Gross Accumulated Amortization Net Gross Accumulated Amortization Net (In millions) Customer relationships $ 79.5 $ (22.7 ) $ 56.8 $ 80.4 $ (19.5 ) $ 60.9 Patents and technology 50.3 (37.9 ) 12.4 46.4 (34.2 ) 12.2 Other 3.2 (1.6 ) 1.6 3.2 (1.5 ) 1.7 Total Intangible Assets $ 133.0 $ (62.2 ) $ 70.8 $ 130.0 $ (55.2 ) $ 74.8
Projected Annual Amortization Expense for Intangible Assets	Projected annual amortization expense for intangible assets as of September 30, 2017 is as follows: 2018 $ 7.2 2019 5.9 2020 5.8 2021 5.8 2022 4.9 Thereafter 41.2 Total $ 70.8

Debt (Tables)

Debt (Tables)	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Schedule of Debt	Components of Debt September 30, 2017 2016 (In millions) Short-term borrowings (A) $ — $ — Current portion of long-term debt 5.8 5.8 Long-term debt 977.0 980.3 Total Debt $ 982.8 $ 986.1 (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 September 30, 2017 is $20.2 million .
Components of Debt	September 30, 2017 2016 (In millions) Term loan facility under Credit Agreement $ 569.3 $ 575.0 Revolving facility under Credit Agreement — — 5.500% Senior Notes due 2024 425.0 425.0 Total debt 994.3 1,000.0 Less debt discount 2.5 2.8 Less deferred debt costs 9.0 11.1 Less current portion of long-term debt 5.8 5.8 Long-term debt payable after one year $ 977.0 $ 980.3
Maturities of Long-term Debt	Maturities of long-term debt are as follows: Total Debt (In millions) Payments due for the year ended September 30, 2018 $ 5.8 2019 5.8 2020 5.8 2021 5.8 2022 5.8 Thereafter 965.3 Total $ 994.3

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2017
Leases [Abstract]
Minimum Payments Due Under Leases	At September 30, 2017 , minimum payments due under leases are as follows: (In millions) 2018 $ 10.1 2019 8.3 2020 6.7 2021 4.1 2022 3.0 Thereafter 1.4 Total $ 33.6

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Carrying Values and Fair Values of Debt	The carrying values and fair values of our derivatives and debt are as follows: September 30, 2017 Fair Value Carrying Value (In millions) Assets Forward Exchange Contracts $ 0.9 $ 0.9 Liabilities Forward Exchange Contracts $ 1.5 $ 1.5 Long-term Debt Senior Notes $ 450.5 $ 425.0 Term Loan Facility 575.7 569.3 Total Long-term debt $ 1,026.2 $ 994.3

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the Fair Value and Balance Sheet Location of Outstanding Derivatives	The table below summarizes the fair values of our derivatives not designated as hedging instruments and balance sheet location of these outstanding derivatives: 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: Year Ended September 30, 2017 (In millions) Forward Exchange Contracts, net of tax: Net loss recognized in other (income) expense, net (A) $ 2.2

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Sep. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following table summarizes the benefit obligation, fair value of the plan assets and the funded status at September 30, 2017 : 2017 (In millions) Change in benefit obligation: Benefit obligation at September 30, 2016 $ — Converted on October 1, 2016 26.5 Service cost 2.3 Interest cost 0.6 Actuarial gain (4.9 ) Benefits paid (1.2 ) Foreign currency impact (0.5 ) Benefit obligation at end of year $ 22.8 Change in plan assets: Fair value of plan assets at September 30, 2016 $ — Converted on October 1, 2016 3.0 Employer contributions 5.0 Benefits paid (1.2 ) Fair value of plan assets at September 30, 2017 $ 6.8 Funded status: Plan assets less than benefit obligation - Net amount recognized $ (16.0 )
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the annual consolidated balance sheets consist of: 2017 (In millions) Non-current liabilities $ (16.0 ) Accumulated other comprehensive loss, net of taxes (2.2 )
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year	Amounts recognized in accumulated other comprehensive loss, net of tax consist of: 2017 (In millions) Balance at September 30, 2016 $ — Converted on October 1, 2016 (6.2 ) Net loss amortized during the year 0.4 Net gain during the year 3.7 Non-controlling interest (0.1 ) Balance at September 30, 2017 $ (2.2 )
Schedule of Net Benefit Costs	The components of net periodic pension costs for our defined benefit pension plans are as follows: 2017 (In millions) Service cost $ 2.3 Interest cost 0.6 Expected return on plan assets (0.1 ) Actuarial loss amortization 0.5 Net periodic pension cost $ 3.3
Schedule of Assumptions Used	Assumptions used in determining the benefit obligation and net periodic pension cost for the year ended September 30, 2017 are presented in the following table as weighted-averages: 2017 (In millions) Benefit obligations: Discount rate 3.2 % Rate of compensation increase 4.1 % Net Periodic Pension Cost: Discount rate 2.3 % Rate of compensation increase 4.9 % Expected rate of return on plan 2.0 % The calculation of the fair value of market-based restricted stock units during the three months ended December 31, 2016 used the following assumptions: (In percentages) Expected volatility 28.7 % Risk-free interest rate 1.4 %
Schedule of Allocation of Plan Assets	The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy discussed in Note 13 , is as follows: 2017 (In millions) Other investments (Level 2) $ 4.1 Insurance contract (Level 3) 2.7 Total $ 6.8
Schedule of Expected Benefit Payments	We expect to make contributions of approximately $0.4 million during 2018. The expected future benefit payments related to the defined benefit plans are shown below. Payments (In millions) 2018 $ 0.8 2019 0.9 2020 1.0 2021 1.1 2022 1.2 2023-2027 11.6
Defined Contribution Plan Disclosures	The following table summarizes our defined contribution expense: 2017 2016 2015 (In millions) Defined contribution expense $ 11.0 $ 5.5 $ 4.5

Share Based Compensation (Table

Share Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	Share-based compensation award cost recognized in the consolidated income statement is summarized below: Year Ended September 30, 2017 (In millions) Before-Tax Share-Based Compensation Award Cost $ 8.3 Income Tax Benefit 2.9 After-Tax Share-Based Compensation Award Cost $ 5.4
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]	Total before-tax share-based compensation award cost by type of program was as follows: Year Ended September 30, 2017 (In millions) Restricted stock units $ 7.5 Stock options 0.2 Director awards 0.6 Before-Tax Share-Based Compensation Cost $ 8.3
Schedule of Assumptions Used	Assumptions used in determining the benefit obligation and net periodic pension cost for the year ended September 30, 2017 are presented in the following table as weighted-averages: 2017 (In millions) Benefit obligations: Discount rate 3.2 % Rate of compensation increase 4.1 % Net Periodic Pension Cost: Discount rate 2.3 % Rate of compensation increase 4.9 % Expected rate of return on plan 2.0 % The calculation of the fair value of market-based restricted stock units during the three months ended December 31, 2016 used the following assumptions: (In percentages) Expected volatility 28.7 % Risk-free interest rate 1.4 %
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]	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, 2016 — $ — Converted on October 1, 2016 0.5 22.85 Granted 0.7 25.30 Paid out (0.1 ) 15.55 Forfeited/adjustments — — Outstanding, September 30, 2017 1.1 $ 25.30
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]	A summary of stock option activity is presented below: 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 — — Forfeited — — Outstanding, September 30, 2017 0.5 $ 18.55 Weighted Average Remaining Contractual Terms (In years) Aggregate Intrinsic Value (In millions, except years) Outstanding, September 30, 2017 5.6 $ 9.6 Exercisable, September 30, 2017 5.6 9.3

Stock Holders Equity (Tables)

Stock Holders Equity (Tables)	12 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss	The table below summarizes changes in accumulated other comprehensive loss (AOCL), net of tax: 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 — (8.7 ) 3.7 (5.0 ) Net transfers from Air Products — 3.8 (6.2 ) (2.4 ) Amounts reclassified from AOCL — — 0.3 0.3 Net current period other comprehensive loss — (4.9 ) (2.2 ) (7.1 ) Other comprehensive loss attributable to non-controlling interest — 1.3 — 1.3 Balance, September 30, 2017 $ (0.2 ) $ (16.0 ) $ (2.2 ) $ (18.4 )
Reclassification out of Accumulated Other Comprehensive Income	The table below summarizes the reclassifications out of accumulated other comprehensive loss and the affected line item on the consolidated income statements: Year Ended September 30, 2017 (In millions) Pension and Postretirement Benefits, net of tax (A) $ 0.3

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of basic and diluted earnings per share: September 30, 2017 2016 2015 (In millions, except per share data) Numerator Net Income Attributable to Versum $ 193.0 $ 212.0 $ 184.1 Denominator Weighted average number of common shares - Basic 108.7 108.7 108.7 Effect of dilutive securities Employee stock option and other award plans 0.7 — — Weighted average number of common shares - Diluted 109.4 108.7 108.7 Earnings Per Common Share Attributable to Versum Net Income Attributable to Versum - Basic $ 1.78 $ 1.95 $ 1.69 Net Income Attributable to Versum - Diluted 1.76 1.95 1.69

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income of U.S. and Foreign Operations Before Taxes	The following table summarizes the income of U.S. and foreign operations before taxes: Year Ended September 30, 2017 2016 2015 (In millions) Income Before Taxes United States $ 28.8 $ 61.6 $ 41.7 Foreign 223.9 217.1 181.2 Total $ 252.7 $ 278.7 $ 222.9
Components of the Provision for Income Taxes	The following table shows the components of the provision for income taxes: Year Ended September 30, 2017 2016 2015 (In millions) Current Tax Provision Federal $ 2.4 $ — $ — State 0.6 0.6 0.5 Foreign 47.0 58.3 31.6 50.0 58.9 32.1 Deferred Tax Provision Federal 1.1 1.3 1.4 State 0.1 0.1 0.1 Foreign 1.6 (1.5 ) (1.9 ) 2.8 (0.1 ) (0.4 ) Income Tax Provision $ 52.8 $ 58.8 $ 31.7
Reconciliation of the Differences Between the United States Federal Statutory Tax Rate and the Effective Tax Rate	ncome tax expense (benefit) differs from the expected amounts based on the statutory U.S. federal tax rate for the years ended September 30, 2017 , 2016 and 2015 as follows: Year Ended September 30, 2017 2016 2015 (In millions) U.S. federal tax $ 88.4 $ 97.5 $ 78.0 State taxes, net of federal benefit 0.5 2.2 1.3 Foreign tax differentials (34.7 ) (30.7 ) (37.4 ) U.S. taxes on foreign earnings (0.3 ) 4.7 (2.0 ) Other credit and incentives (0.8 ) (0.8 ) (0.7 ) Valuation allowance 0.9 (19.2 ) (6.2 ) Other (1.2 ) 5.1 (1.3 ) Income Tax Expense (Benefit) $ 52.8 $ 58.8 $ 31.7
Significant Components of Deferred Tax Assets and Liabilities	The significant components of deferred tax assets and liabilities are as follows: September 30, 2017 2016 (In millions) Gross Deferred Tax Assets Tax loss carryforwards $ 0.5 $ 13.2 Tax credit carryforwards 0.9 64.2 Retirement benefits and compensation accruals 10.9 7.6 Reserves and accruals 1.6 8.4 Other 1.5 3.3 Valuation allowance (0.9 ) (55.6 ) Deferred Tax Assets 14.5 41.1 Gross Deferred Tax Liabilities Intangible assets 9.1 41.0 Plant and equipment 22.9 22.2 Unremitted earnings of foreign entities 0.7 2.3 Partnership investments 0.8 1.3 Other 0.2 6.3 Deferred Tax Liabilities 33.7 73.1 Net Deferred Income Tax Liability $ 19.2 $ 32.0 Deferred tax assets and liabilities are included within the Annual Consolidated Financial Statements as follows: September 30, 2017 2016 (In millions) Other non-current assets $ 18.1 $ 10.8 Deferred tax liabilities 37.3 42.8 Net Deferred Income Tax Liability $ 19.2 $ 32.0
Reconciliation of the Beginning and Ending Amounts of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of the unrecognized tax benefits is as follows: Year Ended September 30, (In millions) 2017 2016 2015 Unrecognized Tax Benefits Balance at beginning of year $ 12.9 $ 10.3 $ 16.0 Additions for tax positions for the current year 2.1 1.9 1.6 Additions for tax positions of prior years 5.2 1.0 0.1 Reductions for tax positions of prior years (0.2 ) (0.1 ) (4.7 ) Statute of limitations expiration (0.1 ) (0.2 ) (2.7 ) Balance at End of Year $ 19.9 $ 12.9 $ 10.3
Major Tax Jurisdictions	We generally remain subject to examination in the following major tax jurisdictions for the years indicated below: Open Tax Years Major Tax Jurisdiction United States 2017 China 2007-2017 South Korea 2010-2017 Taiwan 2012-2017

Supplemental Information (Table

Supplemental Information (Tables)	12 Months Ended
	Sep. 30, 2017
Supplemental Balance Sheet Information [Abstract]
Payables and Accrued Liabilities	September 30, (In millions) 2017 2016 Payables and Accrued Liabilities Trade creditors $ 56.0 $ 41.6 Customer advances 5.3 4.0 Accrued payroll and employee benefits 41.2 33.9 Other costs associated with business separation, restructuring and cost reduction actions 7.9 0.6 Derivatives 1.5 — Other 8.9 5.7 $ 120.8 $ 85.8

Segment and Geographic Inform51

Segment and Geographic Information (Tables)	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Reporting	As of and for the year ended September 30, 2017 2016 2015 (In millions) Sales Materials $ 829.7 $ 756.7 $ 743.4 Delivery Systems and Services 293.6 213.4 265.9 Corporate 3.6 — — Combined Total $ 1,126.9 $ 970.1 $ 1,009.3 Operating Income (Loss) Materials $ 274.4 $ 252.3 $ 213.7 Delivery Systems and Services 71.7 50.8 49.1 Corporate (20.5 ) (23.3 ) (19.2 ) Segment Total 325.6 279.8 243.6 Business separation, restructuring and cost reduction actions (25.5 ) (0.9 ) (21.6 ) Combined Total $ 300.1 $ 278.9 $ 222.0 Depreciation and Amortization Materials $ 43.1 $ 44.4 $ 48.1 Delivery Systems and Services 1.4 2.1 8.3 Corporate 1.5 0.4 0.5 Combined Total $ 46.0 $ 46.9 $ 56.9 Equity Affiliates’ Income Materials $ — $ 0.2 $ 1.0 Combined Total $ — $ 0.2 $ 1.0 Total Assets Materials $ 773.8 $ 733.4 $ 754.8 Delivery Systems and Services 110.9 104.0 92.7 Corporate 362.1 206.4 39.9 Combined Total $ 1,246.8 $ 1,043.8 $ 887.4 Investment in Net Assets of and Advances to Equity Affiliates Materials $ — $ — $ 12.5 Combined Total $ — $ — $ 12.5 Expenditures for Long-Lived Assets Materials $ 45.7 $ 34.4 $ 21.2 Delivery Systems and Services 1.7 0.7 0.8 Corporate 16.6 0.7 0.1 Combined Total $ 64.0 $ 35.8 $ 22.1
Sales by Product Group	Year Ended September 30, 2017 2016 2015 (In millions) Process Materials $ 401.8 $ 387.4 $ 387.3 Advanced Materials 427.9 369.3 356.1 Equipment and Installations 235.4 150.8 208.3 Site Services 58.2 62.6 57.6 Corporate 3.6 — — Total $ 1,126.9 $ 970.1 $ 1,009.3
Geographic Information	Year Ended September 30, 2017 2016 2015 (In millions) Sales to External Customers United States $ 375.7 $ 349.4 $ 361.3 Taiwan 242.8 230.8 236.3 South Korea 304.1 217.2 220.3 China 64.9 53.8 70.9 Europe 63.1 57.8 69.2 Asia, excluding China, Taiwan, and South Korea 76.3 61.1 51.3 Total $ 1,126.9 $ 970.1 $ 1,009.3 September 30, 2017 2016 2015 (In millions) Long-Lived Assets (A) United States $ 170.3 $ 138.3 $ 139.9 South Korea 112.2 112.2 105.0 Taiwan 38.2 36.8 39.7 Asia, excluding Taiwan and South Korea 9.2 9.0 16.4 Europe 0.4 0.2 0.1 Total $ 330.3 $ 296.5 $ 301.1 (A) Long-lived assets include plant and equipment, net.

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table presents the aggregate purchase price allocation, as of September 30, 2017 . Net Assets Acquired (In millions) Accounts receivable $ 1.0 Other current assets 0.1 Inventories 1.4 Properties and Equipment, net 2.4 Goodwill 5.0 Intangible assets 3.7 Other current liabilities (0.4 ) Net assets acquired $ 13.2
Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination	The table below presents the intangible assets acquired as part of the acquisition of Dynaloy and the periods over which they will be amortized on a straight line basis. Amount Weighted Average Amortization Period (In millions, except years) Technology $ 2.8 7 Trademarks 0.9 5 Total $ 3.7

Summary By Quarter (Unaudited)

Summary By Quarter (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Unaudited Results of Operations For Each Quarter	These tables summarize the unaudited results of operations for each quarter of fiscal 2017 and 2016 : For the Quarter Ended December 31, 2016 March 31, 2017 June 30, 2017 September 30, 2017 Total (In millions) Sales $ 270.8 $ 270.8 $ 290.8 $ 294.5 $ 1,126.9 Cost of sales 150.9 154.5 159.6 171.9 636.9 Selling and administrative 30.2 29.5 34.5 31.5 125.7 Research and development 10.3 10.9 11.9 12.0 45.1 Business separation, restructuring and cost reduction actions 3.2 6.1 6.0 10.2 25.5 Other (income) expense, net (2.9 ) (0.1 ) (2.2 ) (1.2 ) (6.4 ) Operating Income 79.1 69.9 81.0 70.1 300.1 Equity affiliates’ income — — — — — Interest expense 11.5 11.6 11.9 12.4 47.4 Income Before Taxes 67.6 58.3 69.1 57.7 252.7 Income tax provision 15.3 11.5 14.4 11.6 52.8 Net Income 52.3 46.8 54.7 46.1 199.9 Less: Net Income Attributable to Non-controlling Interests 1.5 1.9 2.0 1.5 6.9 Net Income Attributable to Versum $ 50.8 $ 44.9 $ 52.7 $ 44.6 $ 193.0 For the Quarter Ended December 31, 2015 March 31, 2016 June 30, 2016 September 30, 2016 Total (In millions) Sales $ 245.5 $ 233.5 $ 242.7 $ 248.4 $ 970.1 Cost of sales 132.4 132.5 135.9 138.7 539.5 Selling and administrative 23.6 25.7 27.3 33.2 109.8 Research and development 10.9 10.2 11.3 11.5 43.9 Business separation, restructuring and cost reduction actions (0.9 ) (1.8 ) 1.1 2.5 0.9 Other (income) expense, net (1.1 ) (1.0 ) (0.3 ) (0.5 ) (2.9 ) Operating Income 80.6 67.9 67.4 63.0 278.9 Equity affiliates’ income 0.2 — — — 0.2 Interest expense — — — 0.4 0.4 Income Before Taxes 80.8 67.9 67.4 62.6 278.7 Income tax provision 13.4 12.2 17.6 15.6 58.8 Net Income 67.4 55.7 49.8 47.0 219.9 Less: Net Income Attributable to Non-controlling Interests 2.2 1.9 2.0 1.8 7.9 Net Income Attributable to Versum $ 65.2 $ 53.8 $ 47.8 $ 45.2 $ 212.0

Basis of Presentation (Details)

Basis of Presentation (Details)	Oct. 01, 2016	Sep. 30, 2017	Sep. 30, 2016
Product lines | Combined sales
Product Information [Line Items]
Concentration risk, percentage		11.00%	12.00%
Product line | Product lines | Combined sales
Product Information [Line Items]
Concentration risk, percentage			1.00%
Product line | Product lines | Operating Income
Product Information [Line Items]
Concentration risk, percentage			1.00%
Affiliated Entity [Member]
Product Information [Line Items]
Stock split conversion ratio	0.5

Major Accounting Policies (Deta

Major Accounting Policies (Details) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accounting Policies [Abstract]
Before-Tax Share-Based Compensation Award Cost	$ 8,300,000	$ 5,000,000	$ 4,700,000
Schedule of Equity Method Investments [Line Items]
Allowance for doubtful accounts	1,000,000	$ 800,000
Residual value of intangible assets	$ 0
Daido Air Products Electronics, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership, percentage		20.00%
Versum Materials
Schedule of Equity Method Investments [Line Items]
Ownership in noncontrolling interest, percentage	74.00%

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	Oct. 01, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Related Party Transaction [Line Items]
Transition Service Agreement, Additional Fee Due Over Cost, Percentage	5.00%
Minimum
Related Party Transaction [Line Items]
Transition Services Agreement Term	12 months
Maximum
Related Party Transaction [Line Items]
Transition Services Agreement Term	24 months
Air Products
Related Party Transaction [Line Items]
Total Allocated Costs		$ 0	$ 21.3	$ 26.3
Cost of sales | Air Products
Related Party Transaction [Line Items]
Total Allocated Costs		0	2.8	3.6
Selling and administrative | Air Products
Related Party Transaction [Line Items]
Total Allocated Costs		0	16.8	17.8
Research and development | Air Products
Related Party Transaction [Line Items]
Total Allocated Costs		0	1	1.4
Business restructuring and cost reduction actions | Air Products
Related Party Transaction [Line Items]
Total Allocated Costs		$ 0	$ 0.7	$ 3.5

Business Separation, Restruct57

Business Separation, Restructuring, and Cost Reduction Actions (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2016USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)position	Sep. 30, 2015USD ($)position
Restructuring Cost and Reserve [Line Items]
Restructuring charge net of business separation costs										$ 4.7	$ (0.7)	$ 21.6
Number of positions eliminated | position											90	260
Carrying value of assets						$ 17.9					$ 17.9
Restructuring charge		$ 10.2	$ 6	$ 6.1	$ 3.2	$ 2.5	$ 1.1	$ (1.8)	$ (0.9)	25.5	0.9	$ 21.6
Operating Segments | Materials
Restructuring Cost and Reserve [Line Items]
Restructuring charge												12.3
Operating Segments | Delivery Systems and Services
Restructuring Cost and Reserve [Line Items]
Restructuring charge												5.8
Corporate, Non-Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charge												3.5
Onsite Ammonia Plant
Restructuring Cost and Reserve [Line Items]
Gain from sale of plants								1.4
Proceeds from sale of plants	$ 17.1							$ 17.1
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charge net of business separation costs										4.7	2.5	14.4
Asset actions
Restructuring Cost and Reserve [Line Items]
Restructuring charge net of business separation costs										$ 0	(3.2)	$ 7.2
Separation
Restructuring Cost and Reserve [Line Items]
Costs incurred from separation											$ 1.6

Business Separation, Restruct58

Business Separation, Restructuring, and Cost Reduction Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 0.6	$ 4.1	$ 0.9
Restructuring charge	4.7	(0.7)	21.6
Cash receipts (payments)	(1.1)	(1.8)	(11.2)
Non-cash expenses	0	(1)	(7.2)
Restructuring reserve, ending balance	4.2	0.6	4.1
Severance and Other Benefits
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0.6	4.1	0.9
Restructuring charge	4.7	2.5	14.4
Cash receipts (payments)	(1.1)	(6)	(11.2)
Non-cash expenses	0	0	0
Restructuring reserve, ending balance	4.2	0.6	4.1
Asset Actions/Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0	0	0
Restructuring charge	0	(3.2)	7.2
Cash receipts (payments)	0	4.2	0
Non-cash expenses	0	(1)	(7.2)
Restructuring reserve, ending balance	$ 0	$ 0	$ 0

Sale of Equity Affiliate (Detai

Sale of Equity Affiliate (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Investment in net assets of and advances to equity affiliates		$ 0				$ 0				$ 0	$ 0	$ 12.5
Income tax provision		11.6	$ 14.4	$ 11.5	$ 15.3	15.6	$ 17.6	$ 12.2	$ 13.4	52.8	58.8	31.7
Equity affiliates’ income		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	0.2	$ 0	0.2	$ 1
Daido Air Products Electronics, Inc. | Disposed of by Sale
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of equity method investment	$ 15.9
Realized gain on sale of equity method investment											0.7
Investment in net assets of and advances to equity affiliates	12.8								12.8
Foreign currency translation loss	$ 2.4								$ 2.4
Income tax provision											5.3
Equity affiliates’ income											$ 1

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Inventory Disclosure [Abstract]
Finished goods	$ 87.6	$ 94
Work in process	20.3	12.3
Raw materials, supplies and other	52.5	29.4
Inventories at FIFO cost	160.4	135.7
Less: Excess of FIFO cost over LIFO cost	(8.8)	(8.3)
Inventories	$ 151.6	$ 127.4

Inventories (Narrative) (Detail

Inventories (Narrative) (Details)	Sep. 30, 2017	Sep. 30, 2016
Inventory Disclosure [Abstract]
Percentage of LIFO inventory	28.00%	32.00%

Plant and Equipment, Net (Detai

Plant and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 955.2	$ 884.7
Less: accumulated depreciation	624.9	588.2
Plant and equipment, net	330.3	296.5	$ 301.1
Land
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 21.8	21.9
Buildings
Property, Plant and Equipment [Line Items]
Useful Life in years	30 years
Plant and equipment, at cost	$ 149.3	147.1
Machinery and Equipment
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	732	689.5
Production facilities
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 479.9	433.6
Production facilities | Minimum
Property, Plant and Equipment [Line Items]
Useful Life in years	10 years
Production facilities | Maximum
Property, Plant and Equipment [Line Items]
Useful Life in years	15 years
Distribution and other
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 252.1	255.9
Distribution and other | Minimum
Property, Plant and Equipment [Line Items]
Useful Life in years	5 years
Distribution and other | Maximum
Property, Plant and Equipment [Line Items]
Useful Life in years	25 years
Cylinders | Minimum
Property, Plant and Equipment [Line Items]
Useful Life in years	10 years
Cylinders | Maximum
Property, Plant and Equipment [Line Items]
Useful Life in years	25 years
Other distribution equipment
Property, Plant and Equipment [Line Items]
Useful Life in years	20 years
Construction in progress
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 52.1	$ 26.2

Plant and Equipment, Net (Narra

Plant and Equipment, Net (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2016USD ($)plant	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Property, Plant and Equipment [Abstract]
Depreciation expense										$ 38.4	$ 39.4	$ 48.1
Long Lived Assets Held-for-sale [Line Items]
Income tax provision		$ 11.6	$ 14.4	$ 11.5	$ 15.3	$ 15.6	$ 17.6	$ 12.2	$ 13.4	$ 52.8	$ 58.8	$ 31.7
Onsite Ammonia Plant
Long Lived Assets Held-for-sale [Line Items]
Number of plants sold | plant	2
Proceeds from sale of plants	$ 17.1							17.1
Gain from sale of plants								1.4
Income tax provision								$ 1.5

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 180.1	$ 167
Goodwill, Acquired During Period	5
Currency translation adjustment	(2.5)	13.1
Goodwill, ending balance	182.6	180.1
Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	162.6	150.6
Goodwill, Acquired During Period	5
Currency translation adjustment	(2.3)	12
Goodwill, ending balance	165.3	162.6
Delivery Systems and Services
Goodwill [Roll Forward]
Goodwill, beginning balance	17.5	16.4
Goodwill, Acquired During Period	0
Currency translation adjustment	(0.2)	1.1
Goodwill, ending balance	$ 17.3	$ 17.5

Goodwill (Narrative) (Details)

Goodwill (Narrative) (Details)	12 Months Ended
	Sep. 30, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

Intangible Assets - Acquired In

Intangible Assets - Acquired Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross	$ 133	$ 130
Accumulated Amortization	(62.2)	(55.2)
Net	70.8	74.8
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross	79.5	80.4
Accumulated Amortization	(22.7)	(19.5)
Net	56.8	60.9
Patents and technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross	50.3	46.4
Accumulated Amortization	(37.9)	(34.2)
Net	12.4	12.2
Other
Acquired Finite-Lived Intangible Assets [Line Items]
Gross	3.2	3.2
Accumulated Amortization	(1.6)	(1.5)
Net	$ 1.6	$ 1.7

Intangible Assets (Narrative) (

Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	$ 7.6	$ 7.5	$ 8.8
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Remaining useful life	17 years
Patents
Finite-Lived Intangible Assets [Line Items]
Remaining useful life	5 years

Intangible Assets - Projected

Intangible Assets - Projected Annual Amortization Expense for Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2,017	$ 7.2
2,018	5.9
2,019	5.8
2,020	5.8
2,021	4.9
Thereafter	41.2
Net	$ 70.8	$ 74.8

Debt Components of Debt (Detail

Debt Components of Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Debt Disclosure [Abstract]
Short-term borrowings	$ 0	$ 0
Current portion of long-term debt	5.8	5.8
Long-term debt	977	980.3
Total Debt	982.8	$ 986.1
Foreign Lines of Credit
Short-term Debt [Line Items]
Availability under line of credit	$ 20.2

Debt Components of Long Term De

Debt Components of Long Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Total debt	$ 994.3	$ 1,000
Less debt discount	2.5	2.8
Less deferred debt costs	9	11.1
Less current portion of long-term debt	5.8	5.8
Long-term debt payable after one year	977	980.3
Term loan facility under credit agreement
Debt Instrument [Line Items]
Total debt	569.3	575
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

Debt Long-term Debt Maturities

Debt Long-term Debt Maturities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Maturities of Long-term Debt [Abstract]
2,018	$ 5.8
2,019	5.8
2,020	5.8
2,021	5.8
2,022	5.8
Thereafter	965.3
Total	$ 994.3	$ 1,000

Debt (Narrative) (Details)

Debt (Narrative) (Details)	Oct. 10, 2017	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Debt Instrument [Line Items]
Original issue discount		$ 2,500,000	$ 2,800,000
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 200,000,000
Commitment fee percentage		0.375%
Fronting fee percentage		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		2.00%
Basis spread on variable rate, reduction		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		0.25%
Line of Credit | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Term Loan Facility
Debt Instrument [Line Items]
Debt instrument, face amount		$ 575,000,000
Effective interest rate (as percent)		3.83%
Term facility, percent original principal annual amortization		1.00%
Term Loan Facility | LIBOR
Debt Instrument [Line Items]
Minimum floor (as percent)		0.75%
Basis spread on variable rate		2.50%
Term Loan Facility | Base Rate
Debt Instrument [Line Items]
Minimum floor (as percent)		1.75%
Basis spread on variable rate		1.50%
Term Loan Facility | Minimum
Debt Instrument [Line Items]
Prepayment amount of excess cash flows, percentage		0.00%
Term Loan Facility | Maximum
Debt Instrument [Line Items]
Prepayment amount of excess cash flows, percentage		50.00%
Senior Notes | 5.5% Senior Notes due 2024
Debt Instrument [Line Items]
Debt instrument, face amount		$ 425,000,000
Interest rate		5.50%
Subsequent Event | Line of Credit | Revolving Credit Facility | Prior Four Quarter Period After Delivery of Financial Statements
Debt Instrument [Line Items]
Net leverage ratio	2
Subsequent Event | Term Loan Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Subsequent Event | Term Loan Facility | LIBOR | Leverage Ratio is Met [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Subsequent Event | Term Loan Facility | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Subsequent Event | Term Loan Facility | Base Rate | Leverage Ratio is Met [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	0.75%

Leases (Details)

Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Leases [Abstract]
Operating leases, rent expense	$ 12.2	$ 7.6	$ 8.4
2,017	10.1
2,018	8.3
2,019	6.7
2,020	4.1
2,021	3
Thereafter	1.4
Total	$ 33.6

Fair Value (Details)

Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	$ 1.5	$ 0
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	1,026.2
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	994.3
Level 2 | Fair Value | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	575.7
Level 2 | Carrying Value | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	569.3
Level 2 | Forward Exchange Contracts | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0.9
Derivative Liability	1.5
Level 2 | Forward Exchange Contracts | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0.9
Derivative Liability	1.5
Level 1 | Fair Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	450.5
Level 1 | Carrying Value | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Long-term debt	$ 425

Financial Instruments (Details)

Financial Instruments (Details) - Not Designated as Hedging Instrument $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)derivative_instrument
Derivative [Line Items]
Number of Derivatives | derivative_instrument	0
Cash Flow Hedge | Forward exchange contracts
Derivative [Line Items]
Maximum remaining term	1 year
Notional Amount | $	$ 158.4

Financial Instruments Fair Valu

Financial Instruments Fair Value and Balance Sheet Location of Outstanding Derivatives (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 1.5	$ 0
Forward exchange contracts | Fair Value | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset	0.9
Derivative Liability	$ 1.5

Financial Instruments Gain or L

Financial Instruments Gain or Loss Related to Forward Contracts (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
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	$ 2.2

Retirement Benefits - Benefit O

Retirement Benefits - Benefit Obligation, Fair Value of Plan Assets and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Change in benefit obligation:
September 30, 2016	$ 0
Converted on October 1, 2016	26.5
Service cost	2.3
Interest cost	0.6
Actuarial gain	(4.9)
Benefits paid	(1.2)
Foreign currency impact	(0.5)
Benefit obligation at end of year	22.8
Change in plan assets:
September 30, 2016	6.8	$ 6.8	$ 0
Converted on October 1, 2016	3
Employer contributions	5
Benefits paid	(1.2)
September 30, 2017	$ 6.8
Funded status:
Plan assets less than benefit obligation - Net amount recognized		$ (16)

Retirement Benefits - Amounts R

Retirement Benefits - Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Non-current liabilities	$ (16)
Accumulated other comprehensive loss, net of taxes	$ (2.2)	$ 0

Retirement Benefits - Amounts80

Retirement Benefits - Amounts Recognized in Accumulated Other Comprehensive Loss (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Compensation and Retirement Disclosure [Abstract]
Balance at September 30, 2016	$ 0
Converted on October 1, 2016	(6.2)
Net loss amortized during the year	0.4
Net gain during the year	3.7
Non-controlling interest	(0.1)
Balance at September 30, 2017	$ (2.2)

Retirement Benefits - Component

Retirement Benefits - Components of Net Periodic Pension Costs (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 2.3
Interest cost	0.6
Expected return on plan assets	(0.1)
Actuarial loss amortization	0.5
Net periodic pension cost	$ 3.3

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Compensation and Retirement Disclosure [Abstract]
Amount to be amortized from accumulated other comprehensive income next fiscal year	$ 0.1
Expected contributions in next fiscal year	$ 0.4

Retirement Benefits - Assumptio

Retirement Benefits - Assumptions Used for Defined Benefit Obligation and Net Periodic Pension Cost (Details)	12 Months Ended
	Sep. 30, 2017
Benefit obligations:
Discount rate	3.20%
Rate of compensation increase	4.10%
Net Periodic Pension Cost:
Discount rate	2.30%
Rate of compensation increase	4.90%
Expected rate of return on plan	2.00%

Retirement Benefits - Fair Valu

Retirement Benefits - Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 6.8	$ 0
Pension plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.8
Pension plan | Other investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.1
Pension plan | Insurance contract | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2.7

Retirement Benefits - Expected

Retirement Benefits - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2017USD ($)
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2,018	$ 0.8
2,019	0.9
2,020	1
2,021	1.1
2,022	1.2
2023-2027	$ 11.6

Retirement Benefits - Defined C

Retirement Benefits - Defined Contribution Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Defined contribution expense	$ 11	$ 5.5	$ 4.5

Share Based Compensation (Detai

Share Based Compensation (Details)	Oct. 01, 2016	Jun. 30, 2017USD ($)	Dec. 31, 2016$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares) | shares				0
Closing stock price (in dollars per share) | $ / shares				$ 38.82
Total intrinsic value of stock options exercised				$ 900,000
Unrecognized compensation cost related to non-vested stock options				100,000
Before-Tax Share-Based Compensation Award Cost				$ 8,300,000	$ 5,000,000	$ 4,700,000
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				700,000
Weighted average grant-date fair value (in dollars per share) | $ / shares				$ 25.30
Share-based compensation costs paid		$ 0		$ 0
Unrecognized compensation cost related to restricted stock units				$ 13,900,000
Weighted average period to recognize compensation costs				2 years 6 months
Total fair value of shares paid out				$ 1,700,000
Before-Tax Share-Based Compensation Award Cost				$ 7,500,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years
Weighted average period to recognize compensation costs				3 months
Exercise period				10 years
Before-Tax Share-Based Compensation Award Cost				$ 200,000
Director awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Award Cost				600,000
Director award per quarter				$ 25,000,000
Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares) | shares				3,300,000
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]
Service period			3 years
Shares granted (in shares) | shares			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			$ 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			$ 28.37
Air Products
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock split conversion ratio	0.5

Share Based Compensation Compen

Share Based Compensation Compensation Awards Cost Recognized (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Before-Tax Share-Based Compensation Award Cost	$ 8.3	$ 5	$ 4.7
Income Tax Benefit	2.9
After-Tax Share-Based Compensation Award Cost	$ 5.4

Share Based Compensation Before

Share Based Compensation Before-tax Share-Based Compensation Award (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Award Cost	$ 8.3	$ 5	$ 4.7
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Award Cost	7.5
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Award Cost	0.2
Director awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-Tax Share-Based Compensation Award Cost	$ 0.6

Share Based Compensation Assump

Share Based Compensation Assumptions used in Calculation of Fair Value of Market-based Restricted Stock Units (Details) - Market-based restricted stock units	12 Months Ended
	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	28.70%
Risk-free interest rate	1.40%

Share Based Compensation Summar

Share Based Compensation Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units shares in Millions	12 Months Ended
	Sep. 30, 2017$ / sharesshares
Shares
Outstanding, September 30, 2016 | shares	0
Converted on October 1, 2016 | shares	0.5
Granted | shares	0.7
Paid out | shares	(0.1)
Forfeited/adjustments | shares	0
Outstanding, September 30, 2017 | shares	1.1
Weighted Average Grant-Date Fair Value
Outstanding, September 30, 2016 | $ / shares	$ 0
Converted on October 1, 2016 | $ / shares	22.85
Granted | $ / shares	25.30
Paid out | $ / shares	15.55
Forfeited/adjustments | $ / shares	0
Outstanding, September 30, 2017 | $ / shares	$ 25.30

Share Based Compensation Summ92

Share Based Compensation Summary of Stock Option Activity (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)$ / sharesshares
Shares
Outstanding, September 30, 2016 | shares	0
Converted on October 1, 2016 | shares	500,000
Granted | shares	0
Exercised | shares	0
Forfeited | shares	0
September 30, 2017 | shares	500,000
Weighted Average Exercise Price
Outstanding, September 30, 2016 | $ / shares	$ 0
Converted on October 1, 2016 | $ / shares	18.37
Granted | $ / shares	0
Exercised | $ / shares	0
Forfeited | $ / shares	0
September 30, 2017 | $ / shares	$ 18.55
Weighted average remaining contractual terms, options outstanding	5 years 7 months
Aggregate intrinsic value, options outstanding | $	$ 9.6
Weighted average remaining contractual terms, options exercisable	5 years 7 months
Aggregate intrinsic value, options exercisable | $	$ 9.3

Stock Holders Equity Changes in

Stock Holders Equity Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ (103.4)	$ 740.7	$ 873.4
Other comprehensive loss before reclassifications	(5)
Net transfers from Air Products	(2.4)
Amounts reclassified from AOCL	0.3
Total Other Comprehensive Income (Loss)	(7.1)	22.8	(48.4)
Other Comprehensive Loss Attributable to Non-controlling Interests	1.3	0	(2.1)
Stockholders' equity, ending balance	24.6	(103.4)	$ 740.7
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(10)
Stockholders' equity, ending balance	(18.4)	(10)
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)
Other comprehensive loss before reclassifications	0
Net transfers from Air Products	0
Amounts reclassified from AOCL	0
Total Other Comprehensive Income (Loss)	0
Other Comprehensive Loss Attributable to Non-controlling Interests	0
Stockholders' equity, ending balance	(0.2)	(0.2)
Foreign currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(9.8)
Other comprehensive loss before reclassifications	(8.7)
Net transfers from Air Products	3.8
Amounts reclassified from AOCL	0
Total Other Comprehensive Income (Loss)	(4.9)
Other Comprehensive Loss Attributable to Non-controlling Interests	1.3
Stockholders' equity, ending balance	(16)	(9.8)
Pension and postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	0
Other comprehensive loss before reclassifications	3.7
Net transfers from Air Products	(6.2)
Amounts reclassified from AOCL	0.3
Total Other Comprehensive Income (Loss)	(2.2)
Other Comprehensive Loss Attributable to Non-controlling Interests	0
Stockholders' equity, ending balance	$ (2.2)	$ 0

Stock Holders Equity Reclassifi

Stock Holders Equity Reclassification Out of Accumulated Other Comprehensive Loss (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Postretirement Benefits, net of tax	$ (0.3)
Pension and Postretirement Benefits, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension and Postretirement Benefits, net of tax	$ (0.3)

Stock Holders Equity Cash Divid

Stock Holders Equity Cash Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 21, 2017	Apr. 19, 2017	Sep. 30, 2017	Jul. 31, 2017	Mar. 31, 2017
Equity [Abstract]
Quarterly cash dividend per share				$ 0.05	$ 0.05
Cash dividend paid	$ 5.4	$ 5.4	$ 10.9

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Numerator
Net Income Attributable to Versum	$ 44.6	$ 52.7	$ 44.9	$ 50.8	$ 45.2	$ 47.8	$ 53.8	$ 65.2	$ 193	$ 212	$ 184.1
Denominator
Weighted average number of common shares - Basic									108,700,000	108,700,000	108,700,000
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Employee stock option and other award plans									700,000	0	0
Weighted average number of common shares - Diluted									109,400,000	108,700,000	108,700,000
Earnings Per Common Share Attributable to Versum
Net Income Attributable to Versum - Basic									$ 1.78	$ 1.95	$ 1.69
Net Income Attributable to Versum - Diluted									$ 1.76	$ 1.95	$ 1.69
Stock Compensation Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									0

Income Taxes - Income Before Ta

Income Taxes - Income Before Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
United States									$ 28.8	$ 61.6	$ 41.7
Foreign									223.9	217.1	181.2
Income Before Taxes	$ 57.7	$ 69.1	$ 58.3	$ 67.6	$ 62.6	$ 67.4	$ 67.9	$ 80.8	$ 252.7	$ 278.7	$ 222.9

Income Taxes - Components of Pr

Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Current Tax Provision
Federal									$ 2.4	$ 0	$ 0
State									0.6	0.6	0.5
Foreign									47	58.3	31.6
Current Income Tax Provision									50	58.9	32.1
Deferred Tax Provision
Federal									1.1	1.3	1.4
State									0.1	0.1	0.1
Foreign									1.6	(1.5)	(1.9)
Deferred Income Tax Provision									2.8	(0.1)	(0.4)
Income Tax Expense	$ 11.6	$ 14.4	$ 11.5	$ 15.3	$ 15.6	$ 17.6	$ 12.2	$ 13.4	$ 52.8	$ 58.8	$ 31.7

Income Taxes - Effective Tax Ra

Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount									$ 88.4	$ 97.5	$ 78
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount									0.5	2.2	1.3
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount									(34.7)	(30.7)	(37.4)
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount									(0.3)	4.7	(2)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount									0.8	0.8	0.7
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount									0.9	(19.2)	(6.2)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount									(1.2)	5.1	(1.3)
Income Tax Expense	$ 11.6	$ 14.4	$ 11.5	$ 15.3	$ 15.6	$ 17.6	$ 12.2	$ 13.4	$ 52.8	$ 58.8	$ 31.7

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
U.S. federal tax	35.00%
Foreign statutory tax rate, minimum (as percent)	17.00%
Income Tax Holiday [Line Items]
Deferred Tax Liabilities, Net	$ 19.2	$ 32
Accrued income taxes	31.4	12.7
Cash taxes paid	42.9
Tax credit carryforwards	0.9	64.2
Decrease in valuation allowance	54.7
Cumulative undistributed earnings	1,070.8
U.S. income and foreign withholding taxes estimate	196.2
Unrecognized tax benefits	19.9	12.9	$ 10.3	$ 16
Unrecognized tax benefits that would impact effective tax rate	$ 19.9	12.6
Foreign Tax Authority
Income Tax Holiday [Line Items]
Tax benefit of holidays, reduction	50.00%
Net benefit of tax holidays	$ 8	$ 7.1	$ 9.6
Loss carryforwards	1.5
Change From Separate Return Method [Member]
Income Tax Holiday [Line Items]
Deferred Tax Liabilities, Net	(17.5)
Accrued income taxes	$ 13

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Gross Deferred Tax Assets
Tax loss carryforwards	$ 0.5	$ 13.2
Tax credit carryforwards	0.9	64.2
Retirement benefits and compensation accruals	10.9	7.6
Reserves and accruals	1.6	8.4
Other	1.5	3.3
Valuation allowance	(0.9)	(55.6)
Deferred Tax Assets	14.5	41.1
Gross Deferred Tax Liabilities
Intangible assets	9.1	41
Plant and equipment	22.9	22.2
Unremitted earnings of foreign entities	0.7	2.3
Partnership investments	0.8	1.3
Other	0.2	6.3
Deferred Tax Liabilities	33.7	73.1
Net Deferred Income Tax Liability	$ 19.2	$ 32

Income Taxes - Net Deferred Inc

Income Taxes - Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Other non-current assets	$ 18.1	$ 10.8
Deferred tax liabilities	37.3	42.8
Net Deferred Income Tax Liability	$ 19.2	$ 32

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 12.9	$ 10.3	$ 16
Additions for tax positions for the current year	2.1	1.9	1.6
Additions for tax positions of prior years	5.2	1	0.1
Reductions for tax positions of prior years	(0.2)	(0.1)	(4.7)
Statute of limitations expiration	(0.1)	(0.2)	(2.7)
Ending balance	$ 19.9	$ 12.9	$ 10.3

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Examinations (Details)	12 Months Ended
	Sep. 30, 2017
United States | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,017
United States | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,017
China | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,007
China | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,017
South Korea | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,010
South Korea | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,017
Taiwan | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,012
Taiwan | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,017

Supplemental Information - Paya

Supplemental Information - Payables and Accrued Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Supplemental Balance Sheet Information [Abstract]
Trade creditors	$ 56	$ 41.6
Customer advances	5.3	4
Accrued payroll and employee benefits	41.2	33.9
Other costs associated with business separation, restructuring and cost reduction actions	7.9	0.6
Derivative Liability	1.5	0
Other	8.9	5.7
Total Payables and Accrued Liabilities	$ 120.8	$ 85.8

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2017USD ($)
Plant and equipment purchases
Long-term Purchase Commitment [Line Items]
Unconditional purchase obligation	$ 30.3

Segment and Geographic Infor107

Segment and Geographic Information (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)segment	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Segment Reporting [Abstract]
Number of primary operating segments | segment	2
United States
Segment Reporting Information [Line Items]
Export sales to third-party customers | $	$ 68.7	$ 75.8	$ 54.2
Customer concentration risk | Combined sales | Customer one
Segment Reporting Information [Line Items]
Concentration risk, percentage	22.00%	21.00%	21.00%
Customer concentration risk | Combined sales | Customer two
Segment Reporting Information [Line Items]
Concentration risk, percentage	13.00%	13.00%	13.00%
Customer concentration risk | Combined sales | Customer three
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	13.00%	11.00%
Product concentration risk | Combined sales
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	12.00%

Segment and Geographic Infor108

Segment and Geographic Information - Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Operating Income (Loss)	70.1	81	69.9	79.1	63	67.4	67.9	80.6	300.1	278.9	222
Business separation, restructuring and cost reduction actions	(10.2)	(6)	(6.1)	(3.2)	(2.5)	(1.1)	1.8	0.9	(25.5)	(0.9)	(21.6)
Depreciation and Amortization									46	46.9	56.9
Equity Affiliates’ Income	0	$ 0	$ 0	$ 0	0	$ 0	$ 0	$ 0.2	0	0.2	1
Total Assets	1,246.8				1,043.8				1,246.8	1,043.8	887.4
Investment in Net Assets of and Advances to Equity Affiliates	0				0				0	0	12.5
Expenditures for Long-Lived Assets									64	35.8	22.1
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)									325.6	279.8	243.6
Operating Segments | Materials
Segment Reporting Information [Line Items]
Sales									829.7	756.7	743.4
Operating Income (Loss)									274.4	252.3	213.7
Business separation, restructuring and cost reduction actions											(12.3)
Depreciation and Amortization									43.1	44.4	48.1
Total Assets	773.8				733.4				773.8	733.4	754.8
Investment in Net Assets of and Advances to Equity Affiliates	0				0				0	0	12.5
Expenditures for Long-Lived Assets									45.7	34.4	21.2
Operating Segments | Delivery Systems and Services
Segment Reporting Information [Line Items]
Sales									293.6	213.4	265.9
Operating Income (Loss)									71.7	50.8	49.1
Business separation, restructuring and cost reduction actions											(5.8)
Depreciation and Amortization									1.4	2.1	8.3
Total Assets	110.9				104				110.9	104	92.7
Expenditures for Long-Lived Assets									1.7	0.7	0.8
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Sales									3.6	0	0
Operating Income (Loss)									(20.5)	(23.3)	(19.2)
Depreciation and Amortization									1.5	0.4	0.5
Total Assets	$ 362.1				$ 206.4				362.1	206.4	39.9
Expenditures for Long-Lived Assets									16.6	0.7	0.1
Segment Reconciling Items
Segment Reporting Information [Line Items]
Business separation, restructuring and cost reduction actions									$ (25.5)	$ (0.9)	$ (21.6)

Segment and Geographic Infor109

Segment and Geographic Information - Sales by Product Group (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenue, Major Customer [Line Items]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Process Materials
Revenue, Major Customer [Line Items]
Sales									401.8	387.4	387.3
Advanced Materials
Revenue, Major Customer [Line Items]
Sales									427.9	369.3	356.1
Equipment and Installations
Revenue, Major Customer [Line Items]
Sales									235.4	150.8	208.3
Site Services
Revenue, Major Customer [Line Items]
Sales									58.2	62.6	57.6
Corp segment
Revenue, Major Customer [Line Items]
Sales									$ 3.6	$ 0	$ 0

Segment and Geographic Infor110

Segment and Geographic Information - Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Long-Lived Assets	330.3				296.5				330.3	296.5	301.1
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									375.7	349.4	361.3
Long-Lived Assets	170.3				138.3				170.3	138.3	139.9
Taiwan
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									242.8	230.8	236.3
Long-Lived Assets	38.2				36.8				38.2	36.8	39.7
South Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									304.1	217.2	220.3
Long-Lived Assets	112.2				112.2				112.2	112.2	105
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									64.9	53.8	70.9
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									63.1	57.8	69.2
Long-Lived Assets	0.4				0.2				0.4	0.2	0.1
Asia, excluding China, Taiwan, and South Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									76.3	61.1	51.3
Long-Lived Assets	$ 9.2				$ 9				$ 9.2	$ 9	$ 16.4

Acquisition - Narrative (Detail

Acquisition - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Purchase price paid in cash for acquisition	$ 13.2	$ 0	$ 0
Goodwill	182.6	$ 180.1	$ 167
Dynaloy, LLC
Business Acquisition [Line Items]
Purchase price paid in cash for acquisition	13.2
Goodwill	$ 5

Acquisition - Purchase Price Al

Acquisition - Purchase Price Allocation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Goodwill	$ 182.6	$ 180.1	$ 167
Net assets acquired	13.2	$ 0	$ 0
Dynaloy, LLC
Business Acquisition [Line Items]
Accounts receivable	1
Other current assets	0.1
Inventories	1.4
Properties and Equipment, net	2.4
Goodwill	5
Intangible assets	3.7
Other current liabilities	(0.4)
Net assets acquired	$ 13.2

Acquisition - Intangibles Busin

Acquisition - Intangibles Business Combination (Details) - Dynaloy, LLC $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Amount of Finite-lived Intangible Assets Acquired	$ 3.7
Technology
Acquired Finite-Lived Intangible Assets [Line Items]
Amount of Finite-lived Intangible Assets Acquired	$ 2.8
Weighted Average Amortization Period	7 years
Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Amount of Finite-lived Intangible Assets Acquired	$ 0.9
Weighted Average Amortization Period	5 years

Subsequent Events (Details)

Subsequent Events (Details) - $ / shares	Oct. 31, 2017	Jul. 31, 2017	Mar. 31, 2017
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share		$ 0.05	$ 0.05
Subsequent Event
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share	$ 0.05

Summary By Quarter (Unaudite115

Summary By Quarter (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 294.5	$ 290.8	$ 270.8	$ 270.8	$ 248.4	$ 242.7	$ 233.5	$ 245.5	$ 1,126.9	$ 970.1	$ 1,009.3
Cost of sales	171.9	159.6	154.5	150.9	138.7	135.9	132.5	132.4	636.9	539.5	616.5
Selling and administrative	31.5	34.5	29.5	30.2	33.2	27.3	25.7	23.6	125.7	109.8	109.6
Research and development	12	11.9	10.9	10.3	11.5	11.3	10.2	10.9	45.1	43.9	40.7
Business separation, restructuring and cost reduction actions	10.2	6	6.1	3.2	2.5	1.1	(1.8)	(0.9)	25.5	0.9	21.6
Other (income) expense, net	(1.2)	(2.2)	(0.1)	(2.9)	(0.5)	(0.3)	(1)	(1.1)	(6.4)	(2.9)	(1.1)
Operating Income	70.1	81	69.9	79.1	63	67.4	67.9	80.6	300.1	278.9	222
Equity affiliates’ income	0	0	0	0	0	0	0	0.2	0	0.2	1
Interest expense	12.4	11.9	11.6	11.5	0.4	0	0	0	47.4	0.4	0.1
Income Before Taxes	57.7	69.1	58.3	67.6	62.6	67.4	67.9	80.8	252.7	278.7	222.9
Income tax provision	11.6	14.4	11.5	15.3	15.6	17.6	12.2	13.4	52.8	58.8	31.7
Net Income	46.1	54.7	46.8	52.3	47	49.8	55.7	67.4	199.9	219.9	191.2
Less: Net Income Attributable to Non-controlling Interests	1.5	2	1.9	1.5	1.8	2	1.9	2.2	6.9	7.9	7.1
Net Income Attributable to Versum	$ 44.6	$ 52.7	$ 44.9	$ 50.8	$ 45.2	$ 47.8	$ 53.8	$ 65.2	$ 193	$ 212	$ 184.1

Schedule II-Valuation and Qu116

Schedule II-Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 0.8	$ 0.8	$ 2.2
Change Charged to Expense	0.2	0	0.1
Other Changes	0	0	(1.5)
Balance at End of Period	1	0.8	0.8
Allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	55.6	77.7	83.3
Change Charged to Expense	0.9	(20.8)	(4.9)
Other Changes	(55.6)	(1.3)	(0.7)
Balance at End of Period	$ 0.9	$ 55.6	$ 77.7