Trinseo (TSE) 10-Q 9 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 07, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Entity Registrant Name	Trinseo S.A.
Entity Central Index Key	1,519,061
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		42,320,717

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 421.4	$ 432.8
Accounts receivable, net of allowance for doubtful accounts (September 30, 2018: $5.0; December 31, 2017: $5.6)	753.1	685.5
Inventories	585.6	510.4
Other current assets	39	17.5
Total current assets	1,799.1	1,646.2
Investments in unconsolidated affiliates	180.8	152.5
Property, plant and equipment, net of accumulated depreciation (September 30, 2018: $579.3; December 31, 2017: $523.7)	594.3	627
Other assets
Goodwill	69.9	72.5
Other intangible assets, net	195.7	207.5
Deferred income tax assets	32.5	35.5
Deferred charges and other assets	37.7	30.8
Total other assets	335.8	346.3
Total assets	2,910	2,772
Current liabilities
Short-term borrowings and current portion of long-term debt	7	7
Accounts payable	459.9	436.8
Income taxes payable	19.6	35.9
Accrued expenses and other current liabilities	141.7	146.9
Total current liabilities	628.2	626.6
Noncurrent liabilities
Long-term debt, net of unamortized deferred financing fees	1,161.7	1,165
Deferred income tax liabilities	46.4	49.2
Other noncurrent obligations	247.5	256.4
Total noncurrent liabilities	1,455.6	1,470.6
Commitments and contingencies (Note 11)
Shareholders' equity
Ordinary shares, $0.01 nominal value, 50,000.0 shares authorized (September 30, 2018: 48.8 shares issued and 42.5 shares outstanding; December 31, 2017: 48.8 shares issued and 43.4 shares outstanding)	0.5	0.5
Additional paid-in-capital	572.2	578.8
Treasury shares, at cost (September 30, 2018: 6.3 shares; December 31, 2017: 5.4 shares)	(367.6)	(286.8)
Retained earnings	770.9	527.9
Accumulated other comprehensive loss	(149.8)	(145.6)
Total shareholders' equity	826.2	674.8
Total liabilities and shareholders' equity	$ 2,910	$ 2,772

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Allowance for doubtful accounts	$ 5	$ 5.6
Accumulated depreciation	$ 579.3	$ 523.7
Ordinary shares, nominal value	$ 0.01	$ 0.01
Ordinary shares, shares authorized	50,000,000,000	50,000,000,000
Ordinary shares, shares issued	48,800,000	48,800,000
Ordinary shares, shares outstanding	42,500,000	43,400,000
Treasury stock, shares	6,300,000	5,400,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statements of Operations
Net sales	$ 1,199.7	$ 1,096.6	$ 3,557.8	$ 3,346.3
Cost of sales	1,068.1	948.1	3,088.3	2,872.3
Gross profit	131.6	148.5	469.5	474
Selling, general and administrative expenses	60	65	186.1	179.3
Equity in earnings of unconsolidated affiliates	34.5	43.8	113.3	93
Operating income	106.1	127.3	396.7	387.7
Interest expense, net	10.1	18.4	35.8	55.4
Loss on extinguishment of long-term debt		65.3	0.2	65.3
Other expense (income), net	2.1	2.1	2.9	(0.1)
Income before income taxes	93.9	41.5	357.8	267.1
Provision for income taxes	19.2	8.3	64.5	56.4
Net income	$ 74.7	$ 33.2	$ 293.3	$ 210.7
Weighted average shares- basic	42.6	43.7	43	43.9
Net income per share- basic	$ 1.75	$ 0.76	$ 6.82	$ 4.80
Weighted average shares- diluted	43.3	44.8	43.9	45
Net income per share- diluted	$ 1.72	$ 0.74	$ 6.68	$ 4.68
Dividends on ordinary shares	$ 0.40	$ 0.36	$ 1.16	$ 1.02

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statements of Comprehensive Income (Loss)
Net income	$ 74.7	$ 33.2	$ 293.3	$ 210.7
Other comprehensive income (loss), net of tax
Cumulative translation adjustments	(4.6)	(1.6)	(22.8)	21.6
Net gain (loss) on cash flow hedges	2.1	(3.7)	16.8	(21.5)
Amounts reclassified from accumulated other comprehensive income (loss)	0.6	0.8	1.8	3
Total other comprehensive income (loss), net of tax	(1.9)	(4.5)	(4.2)	3.1
Comprehensive income	$ 72.8	$ 28.7	$ 289.1	$ 213.8

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Ordinary Shares	Additional Paid-In Capital	Treasury Shares	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total
Balance at beginning of period at Dec. 31, 2016	$ 0.5	$ 573.7	$ (217.5)	$ (170.2)	$ 261.2	$ 447.7
Balance at beginning of period, shares at Dec. 31, 2016	44.3		4.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					210.7	210.7
Other comprehensive loss				3.1		3.1
Stock-based compensation		3.1	$ 15.7			18.8
Stock-based compensation, shares from treasury stock	0.4		(0.4)
Purchase of treasury shares			$ (61.9)			(61.9)
Purchase of treasury shares, shares	(1)		1
Dividends on ordinary shares					(45.8)	(45.8)
Balance at end of period at Sep. 30, 2017	$ 0.5	576.8	$ (263.7)	(167.1)	426.1	572.6
Balance at end of period, shares at Sep. 30, 2017	43.7		5.1
Balance at beginning of period at Jun. 30, 2017				(162.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income						33.2
Other comprehensive loss						(4.5)
Balance at end of period at Sep. 30, 2017	$ 0.5	576.8	$ (263.7)	(167.1)	426.1	572.6
Balance at end of period, shares at Sep. 30, 2017	43.7		5.1
Balance at beginning of period at Dec. 31, 2017	$ 0.5	578.8	$ (286.8)	(145.6)	527.9	$ 674.8
Balance at beginning of period, shares at Dec. 31, 2017	43.4		5.4			43.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					293.3	$ 293.3
Other comprehensive loss				(4.2)		(4.2)
Stock-based compensation		(6.6)	$ 13.4			6.8
Stock-based compensation, shares from treasury stock	0.4		(0.4)
Purchase of treasury shares			$ (94.2)			(94.2)
Purchase of treasury shares, shares	(1.3)		1.3
Dividends on ordinary shares					(50.3)	(50.3)
Balance at end of period at Sep. 30, 2018	$ 0.5	572.2	$ (367.6)	(149.8)	770.9	$ 826.2
Balance at end of period, shares at Sep. 30, 2018	42.5		6.3			42.5
Balance at beginning of period at Jun. 30, 2018				(147.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income						$ 74.7
Other comprehensive loss						(1.9)
Balance at end of period at Sep. 30, 2018	$ 0.5	$ 572.2	$ (367.6)	$ (149.8)	$ 770.9	$ 826.2
Balance at end of period, shares at Sep. 30, 2018	42.5		6.3			42.5

Consolidate Statements of Share

Consolidate Statements of Shareholders' Equity (Parenthetical)) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statement of Stockholders' Equity
Dividends on ordinary shares	$ 0.40	$ 0.36	$ 1.16	$ 1.02

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 293.3	$ 210.7
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	96	80.1
Amortization of deferred financing fees, issuance discount, and excluded component of hedging instruments	0.8	4
Deferred income tax	2.1	(2.6)
Stock-based compensation expense	12.3	10.8
Earnings of unconsolidated affiliates, net of dividends	(28.3)	(4.1)
Unrealized net gains on foreign exchange forward contracts	(5.4)	(2.8)
Loss on extinguishment of long-term debt	0.2	65.3
Gain on sale of businesses and other assets	(0.5)	(10.5)
Impairment charges	0.4	4.3
Changes in assets and liabilities
Accounts receivable	(77.8)	(92.8)
Inventories	(86.1)	(57.3)
Accounts payable and other current liabilities	46.4	(1)
Income taxes payable	(16.3)	6.3
Other assets, net	(17.2)	(14.4)
Other liabilities, net	18.6	(1.2)
Cash provided by operating activities	238.5	194.8
Cash flows from investing activities
Capital expenditures	(90.9)	(108.9)
Cash paid to acquire a business, net of cash acquired		(79.7)
Proceeds from capital expenditures subsidy	1
Proceeds from the sale of businesses and other assets	1.8	46.2
Distributions from unconsolidated affiliates		0.9
Cash used in investing activities	(88.1)	(141.5)
Cash flows from financing activities
Deferred financing fees	(0.6)	(19.2)
Short term borrowings, net	(0.2)	(0.2)
Purchase of treasury shares	(95.5)	(65.2)
Dividends paid	(49)	(42.2)
Proceeds from exercise of option awards	2.6	8.3
Withholding taxes paid on restricted share units	(8.1)	(0.2)
Net proceeds from issuance of Term Loan B	696.5	700
Prepayment penalty on long-term debt		(53)
Cash used in financing activities	(156.1)	(210.2)
Effect of exchange rates on cash	(5.7)	10.5
Net change in cash and cash equivalents	(11.4)	(146.4)
Cash and cash equivalents, beginning of period	432.8	465.1
Cash and cash equivalents, end of period	421.4	318.7
2021 Term Loan B
Cash flows from financing activities
Repayments of Term Loans		(492.5)
2024 Term Loan B
Cash flows from financing activities
Repayments of Term Loans	$ (701.8)
2025 Senior Notes
Cash flows from financing activities
Proceeds from issuance of Senior Notes		500
2022 Senior Notes
Adjustments to reconcile net income to net cash provided by operating activities
Loss on extinguishment of long-term debt		65.3
Cash flows from financing activities
Repayments of Senior Notes		(746)
Prepayment penalty on long-term debt		$ (53)

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Basis of Presentation.
Basis of Presentation	NOTE 1—BASIS OF PRESENTATION The unaudited interim condensed consolidated financial statements of Trinseo S.A. and its subsidiaries (the “Company”) as of and for the periods ended September 30, 2018 and 2017 were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and reflect all adjustments, consisting only of normal recurring adjustments, which, in the opinion of management, are considered necessary for the fair statement of the results for the periods presented. Because they cover interim periods, the statements and related notes to the financial statements do not include all disclosures normally provided in annual financial statements, and therefore, these statements should be read in conjunction with the 2017 audited consolidated financial statements included within the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (“SEC”) on March 1, 2018. The December 31, 2017 condensed consolidated balance sheet data presented herein was derived from the Company’s December 31, 2017 audited consolidated financial statements, but does not include all disclosures required by GAAP for annual periods. Certain prior year amounts have been reclassified to conform to the current period presentation. These reclassifications did not have a material impact on the Company’s financial position or results. Refer to Notes 2, 7, and 15 for further information.

Recent Accounting Guidance

Recent Accounting Guidance	9 Months Ended
	Sep. 30, 2018
Recent Accounting Guidance
Recent Accounting Guidance	NOTE 2—RECENT ACCOUNTING GUIDANCE In May 2014, the Financial Accounting Standards Board (“FASB”) and the International Accounting Standards Board (“IASB”) jointly issued guidance (“Topic 606”) which clarifies the principles for recognizing revenue and develops a common revenue standard for GAAP and International Financial Reporting Standards (“IFRS”). The core principle of the guidance, which the FASB issued certain clarifying updates for, is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company adopted Topic 606 effective January 1, 2018, electing to apply the modified retrospective approach only to contracts that were not completed as of the date of initial application at the individual contract level, rather than applying the portfolio approach. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts have not been adjusted and continue to be reported in accordance with historical accounting standards (“Topic 605”). As a result of the Company’s implementation procedures, the Company has determined that the cumulative effect to retained earnings from initially applying Topic 606 was immaterial and therefore, no adjustment was recorded. Furthermore, based on current contracts with customers, the Company does not expect the adoption of the new revenue standard to have a material impact to its financial statements on an ongoing basis. Refer to Note 3 for new disclosure requirements in effect as a result of this adoption. In February 2016, the FASB issued guidance related to leases that outlines a comprehensive lease accounting model and supersedes the current lease guidance. The new guidance requires lessees to recognize on the consolidated balance sheets lease liabilities and corresponding right-of-use assets for all leases with terms of greater than 12 months. It also changes the definition of a lease and expands the disclosure requirements of lease arrangements. Although early adoption is permitted, the Company will adopt this new guidance on the effective date for public companies of January 1, 2019. The new guidance must be adopted using a modified retrospective transition, applying the new standard to all leases existing at the date of initial application, which will be the effective date of January 1, 2019. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company has completed its risk assessment and scoping procedures for the adoption of this guidance through a number of procedures, including conducting surveys with relevant stakeholders in the business, evaluating its known lease population and data constraints, and selecting the leasing software tool that will be utilized in the adoption. The Company remains in the process of implementing this tool, evaluating available practical expedients and accounting policy elections, assessing new disclosure requirements, designing and implementing key controls, and quantifying the expected impact of the adoption on its consolidated financial statements. However, as the Company is the lessee under various real estate, railcar, and other equipment leases, which it currently accounts for as operating leases, the Company currently anticipates the most significant impact of this adoption will be the recognition of right-of-use assets and lease liabilities on the consolidated balance sheet . In March 2017, the FASB issued guidance that requires employers to present the service cost component of net periodic benefit cost in the same line item within the statements of operations as other employee compensation costs arising from services rendered during the period. The other components of net periodic benefit cost are to be presented outside of any subtotal of operating income. This guidance also requires employers to prospectively only consider the service cost component of net periodic benefit cost for potential capitalization into assets, with all other components of net periodic benefit cost being ineligible for capitalization. The Company adopted this guidance effective January 1, 2018 on a retrospective basis. As a result of this adoption, for the three and nine months ended September 30, 2017, the Company reclassified net periodic benefit cost of $1.4 million and $3.8 million, respectively, from “Cost of sales” and $0.7 million and $2.2 million, respectively, from “Selling, general and administrative expenses” to “Other expense (income), net” within the condensed consolidated statements of operations. The change related to capitalization guidance is not expected to have a material impact on the Company’s consolidated financial statements. In August 2017, the FASB issued significant amendments to its existing hedge accounting guidance. Among other things, this guidance intends to make more financial and nonfinancial hedging strategies eligible for hedge accounting, amend presentation and disclosure requirements, and changes how companies assess effectiveness. Specifically, the guidance eliminates the requirement to separately measure and record ineffectiveness for cash flow and net investment hedges. The Company adopted this guidance effective April 1, 2018. Based upon the Company’s hedging portfolio, this adoption did not result in any cumulative-effect adjustments to retained earnings. The amended presentation and disclosure guidance will be applied prospectively. Refer to Note 8 for further information regarding the impacts of this adoption as well as additional disclosures required by this standard. In February 2018, the FASB issued guidance to address certain stranded income tax effects in accumulated other comprehensive income/loss (“AOCI”) resulting from the enactment of the U.S. “Tax Cuts and Jobs Act” signed into law on December 22, 2017. The amendment provides financial statement preparers with an option to reclassify stranded tax effects within AOCI, resulting from the reduction of the U.S. federal corporate income tax rate, to retained earnings. The amendment also includes disclosure requirements regarding the Company’s accounting policy for releasing income tax effects from AOCI. The amendment is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2018. Early adoption is permitted, and the provisions of the amendment should be applied either in the period of adoption or retrospectively to each period in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized. While the Company is still evaluating the provisions of this amendment, should the Company choose to adopt this guidance, it is not expected to have a material impact on the Company’s consolidated financial statements . In August 2018, the FASB issued guidance which modifies the disclosure requirements for employers that sponsor defined benefit pension plans or other postretirement plans. This amendment is effective for public companies for fiscal years ending after December 15, 2020. Early adoption is permitted, and the provisions of the amendment should be applied on a retrospective basis to all periods presented. The Company is currently assessing the impact of adopting this guidance on its consolidated financial statements. In August 2018, the FASB issued guidance which aligns the requirements for capitalizing implementation costs incurred in a cloud computing hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This standard update is effective for public companies for interim and annual periods beginning after December 15, 2019, with early adoption permitted. Entities may choose to adopt the new guidance either retrospectively or prospectively to eligible costs incurred on or after the date first applied. The Company is currently assessing the impact of adopting this guidance on its consolidated financial statements.

Net Sales

Net Sales	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Net Sales	NOTE 3 — NET SALES As discussed in Note 2, effective January 1, 2018, the Company adopted accounting guidance, Topic 606, issued by the FASB related to the recognition of revenue from contracts with customers. The Company’s accounting policy and practical expedient elections related to revenue recognition, including those elected as a result of the adoption of Topic 606, are summarized as follows. Sales are recognized at a point when control of the promised goods or services is transferred to the customer in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services, and when the Company’s related performance obligation is satisfied under the terms of the contract. Standard terms of delivery are included in contracts of sale, order confirmation documents, and invoices. Sales and other taxes that the Company collects concurrent with sales-producing activities are excluded from “Net sales” and included as a component of “Cost of sales” in the condensed consolidated statements of operations. Additionally, freight and any directly related costs of transporting finished products to customers are accounted for as fulfilment costs and are also included within “Cost of sales”. The amount of net sales recognized varies with changes in returns, rebates, cash sales incentives, and other allowances offered to customers based on the Company's experience. The Company has elected to apply the following practical expedients as allowed under Topic 606: · The incremental costs of obtaining contracts are expensed as incurred if the amortization period of the assets that the Company otherwise would have recognized is one year or less, and are included within “Selling, general and administrative expenses” in the condensed consolidated statements of operations. · When the period between customer payment and transfer of goods/services is determined to be one year or less at contract inception, the promised amount of consideration under the contract is not adjusted for the effects of a significant financing component. · In consideration of the disclosure requirements regarding the transaction price and expected period of recognition of remaining performance obligations that are unsatisfied as of the end of a reporting period, the Company has elected the following optional exemptions: o The Company will not disclose the aggregate amount of the transaction price allocated to remaining performance obligations for its contracts with an original expected duration of one year or less, which applies to the vast majority of the Company’s contracts with customers. o For contracts with customers containing variable consideration (via enforceable minimum volume requirements) and an original expected duration greater than one year, the Company will not disclose the transaction price allocated to remaining performance obligations if the variable consideration is allocated entirely to a wholly unsatisfied performance obligation. Under these contracts with customers, each unit of production generally represents a separate performance obligation, the pricing for which is based on current or forecasted raw material prices, often using formulas that utilize commodity indices. Therefore, future volumes are wholly unsatisfied and disclosure of the transaction price allocated to remaining performance obligations is not required. The variable consideration in these contracts is resolved typically at the issuance of a purchase order or as of the date of revenue recognition. The following table provides disclosure of net sales to external customers by primary geographical market (based on the location where sales originated), by segment for the three and nine months ended September 30, 2018 and 2017: Latex Synthetic Performance Three Months Ended Binders Rubber Plastics Polystyrene Feedstocks Total September 30, 2018 United States $ 77.3 $ — $ 87.0 $ — $ 3.0 $ 167.3 Europe 117.0 137.7 226.7 148.3 61.2 690.9 Asia-Pacific 80.0 — 62.7 104.0 66.8 313.5 Rest of World 3.7 — 24.3 — — 28.0 Total $ 278.0 $ 137.7 $ 400.7 $ 252.3 $ 131.0 $ 1,199.7 September 30, 2017 (1) United States $ 73.7 $ — $ 76.8 $ 0.1 $ 3.5 $ 154.1 Europe 113.0 118.7 223.6 144.9 61.8 662.0 Asia-Pacific 75.3 — 39.1 93.4 45.7 253.5 Rest of World 4.3 — 22.7 — — 27.0 Total $ 266.3 $ 118.7 $ 362.2 $ 238.4 $ 111.0 $ 1,096.6 Latex Synthetic Performance Nine Months Ended Binders Rubber Plastics Polystyrene Feedstocks Total September 30, 2018 United States $ 216.3 $ — $ 253.7 $ 0.2 $ 9.6 $ 479.8 Europe 349.6 442.2 720.9 460.9 174.5 2,148.1 Asia-Pacific 236.9 — 171.0 316.4 123.6 847.9 Rest of World 11.4 — 70.6 — — 82.0 Total $ 814.2 $ 442.2 $ 1,216.2 $ 777.5 $ 307.7 $ 3,557.8 September 30, 2017 (1) United States $ 228.7 $ — $ 230.6 $ 0.8 $ 10.2 $ 470.3 Europe 361.2 456.1 634.0 427.9 145.9 2,025.1 Asia-Pacific 243.6 — 106.8 271.5 148.8 770.7 Rest of World 13.2 — 67.0 — — 80.2 Total $ 846.7 $ 456.1 $ 1,038.4 $ 700.2 $ 304.9 $ 3,346.3 (1) As the Company has adopted Topic 606 utilizing the modified retrospective approach, amounts for the three and nine months ended September 30, 2017 above are disclosed as recognized under Topic 605. For all material contracts with customers, control is transferred and sales are recognized at a point in time when the Company satisfies the performance obligations according to the terms of the contract, and when title and the risk of loss is passed to the customer. Title and risk of loss varies by region and customer and is determined based upon the purchase order received from the customer and the applicable contractual terms or jurisdictional standards. The Company receives cash equal to the invoice price for most product sales, subject to cash sales incentives with certain customers, with payment terms generally ranging from 10 to 90 days (with an approximate weighted average of 53 days as of September 30, 2018), also varying by segment and region. Certain of the Company’s contracts with customers contain multiple performance obligations, most commonly due to the sale of multiple distinct products. The transaction price within these contracts is allocated between these separate and distinct products based on their stand-alone selling prices, as defined within the contract. The Company’s products are typically sold at observable stand-alone sales values, which are used to determine the estimated stand-alone selling price. The stand-alone selling prices of the Company’s products are generally based, in part, on the current or forecasted costs of key raw materials, but are often subject to a predetermined lag period for the pass through of these costs. As such, contracts with customers typically include provisions that allow for the changes in stand-alone selling prices to reflect the pass through of changes in raw material costs, often using pricing formulas that utilize commodity indices. In cases where the Company’s transaction price is considered variable at the point of revenue recognition, the ‘most likely amount’ method is used to estimate the effect of any related uncertainty. In formulating this estimate, the Company considers all historical, current, and forecasted information that is reasonably available to identify a reasonable number of possible consideration amounts. Once the transaction price, including impacts of variable consideration, is estimated, revenue is recognized only to the extent that it is probable that a subsequent change in the estimate would not result in a significant revenue reversal. Furthermore, if the Company is not able to rely on observable stand-alone selling prices, the ‘expected cost plus a margin approach’ is utilized to estimate the stand-alone selling price of each performance obligation, primarily utilizing historical experience. During the three and nine months ended September 30, 2018, the impact of recognizing changes in selling prices related to prior periods was immaterial.

Investments in Unconsolidated A

Investments in Unconsolidated Affiliates	9 Months Ended
	Sep. 30, 2018
Investments in Unconsolidated Affiliates
Investments in Unconsolidated Affiliates	NOTE 4—INVESTMENTS IN UNCONSOLIDATED AFFILIATES The Company is currently supplemented by one joint venture, A mericas Styrenics LLC (“Americas Styrenics”, a styrene and polystyrene joint venture with Chevron Phillips Chemical Company LP). Previously, the Company also had a 50% share in Sumika Styron Polycarbonate Limited (“Sumika Styron Polycarbonate”, a polycarbonate, or PC, joint venture with Sumitomo Chemical Company Limited), until the sale of the Company’s investment in the joint venture during the first quarter of 2017 (refer to discussion below for further information). Investments held in unconsolidated affiliates are accounted for by the equity method. The results of Americas Styrenics are included within its own reporting segment. The results of Sumika Styron Polycarbonate were included within the Performance Plastics reporting segment (as recast, due to the segment realignment effective January 1, 2018 discussed further in Note 15) until the Company sold its share of the entity during the first quarter of 2017. Both of the unconsolidated affiliates are privately held companies; therefore, quoted market prices for their stock are not available. The summarized financial information of the Company’s unconsolidated affiliates is shown below. This table includes summarized financial information for Sumika Styron Polycarbonate through the date of sale in January 2017. Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Sales $ 462.1 $ 458.7 $ 1,430.2 $ 1,369.6 Gross profit $ 74.1 $ 90.6 $ 242.3 $ 176.4 Net income $ 62.1 $ 81.1 $ 206.4 $ 141.5 Americas Styrenics As of September 30, 2018 and December 31, 2017, the Company’s investment in Americas Styrenics was $180.8 million and $152.5 million, respectively, which was $36.6 million and $46.4 million less than the Company’s 50% share of the underlying net assets of Americas Styrenics, respectively . This amount represents the difference between the book value of assets contributed to the joint venture at the time of formation (May 1, 2008) and the Company’s 50% share of the total recorded value of the joint venture’s assets and certain adjustments to conform with the Company’s accounting policies. This difference is being amortized over a weighted average remaining useful life of the contributed assets of approximately 2.1 years as of September 30, 2018. The Company received dividends from Americas Styrenics of $17.5 million and $85.0 million during the three and nine months ended September 30, 2018, respectively, compared to $35.0 million and $80.0 million during the three and nine months ended September 30, 2017, respectively. Sumika Styron Polycarbonate On January 31, 2017, the Company completed the sale of its 50% share in Sumika Styron Polycarbonate to Sumitomo Chemical Company Limited for total sales proceeds of approximately $42.1 million. As a result, the Company recorded a gain on sale of $9.3 million during the nine months ended September 30, 2017, which was included within “Other expense (income), net” in the condensed consolidated statements of operations and was allocated entirely to the Performance Plastics segment (as recast under the segment realignment discussed further in Note 15). In addition, the parties entered into a long-term agreement to continue sourcing PC resin from Sumika Styron Polycarbonate to the Company’s Performance Plastics segment. Due to the sale in January 2017, the Company no longer had an investment in Sumika Styron Polycarbonate as of December 31, 2017. The Company received dividends from Sumika Styron Polycarbonate of zero and $9.8 million during the three and nine months ended September 30, 2017, respectively, related to the Company’s proportionate share of earnings from the year ended December 31, 2016.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2018
Inventories
Inventories	NOTE 5—INVENTORIES Inventories consisted of the following: September 30, December 31, 2018 2017 Finished goods $ 292.7 $ 250.9 Raw materials and semi-finished goods 254.9 226.7 Supplies 38.0 32.8 Total $ 585.6 $ 510.4

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt
Debt	NOTE 6—DEBT Refer to the Annual Report for definitions of capitalized terms not included herein and further background on the Company’s debt structure discussed below. The Company was in compliance with all debt related covenants as of September 30, 2018 and December 31, 2017. As of September 30, 2018 and December 31, 2017, debt consisted of the following: September 30, 2018 December 31, 2017 Interest Rate as of Maturity Carrying Unamortized (1) Total Debt, Carrying Unamortized (1) Total Debt, Senior Credit Facility 2022 Revolving Facility (2) Various September 2022 $ — $ — $ — $ — $ — $ — 2024 Term Loan B (3) 4.242% September 2024 693.0 (16.9) 676.1 698.3 (18.3) 680.0 2025 Senior Notes 5.375% September 2025 500.0 (8.6) 491.4 500.0 (9.4) 490.6 Accounts Receivable Securitization Facility (4) Various September 2021 — — — — — — Other indebtedness Various Various 1.2 — 1.2 1.4 — 1.4 Total debt $ 1,194.2 $ (25.5) $ 1,168.7 $ 1,199.7 $ (27.7) $ 1,172.0 Less: current portion (7.0) (7.0) Total long-term debt, net of unamortized deferred financing fees $ 1,161.7 $ 1,165.0 (1) This caption does not include deferred financing fees related to the Company’s revolving facilities, which are included within “Deferred charges and other assets” on the condensed consolidated balance sheets. (2) Under the 2022 Revolving Facility, the Company had a capacity of $375.0 million and funds available for borrowing of $360.5 million (net of $14.5 million outstanding letters of credit) as of September 30, 2018. Additionally, the Company is required to pay a quarterly commitment fee in respect of any unused commitments under this facility equal to 0.375% per annum. (3) As of September 30, 2018, $7.0 million of the scheduled future payments related to this facility were classified as current debt on the Company’s condensed consolidated balance sheet. (4) This facility had a borrowing capacity of $150.0 million as of September 30, 2018. Additionally, a s of September 30, 2018, the Company had accounts receivable available to support this facility in excess of its borrowing capacity, based on the pool of eligible accounts receivable. In regard to outstanding borrowings, fixed interest charges are 1.95% plus variable commercial paper rates, while for available, but undrawn commitments, fixed interest charges are 1.00%. As a result of an amendment that was executed during the third quarter of 2018, this facility now has a maturity date of September 2021. 2024 Term Loan B Repricing On May 22, 2018, Trinseo Materials Operating S.C.A. and Trinseo Materials Finance, Inc. (together, the “Issuers” or the “Borrowers”), both wholly-owned subsidiaries of the Company, successfully repriced the effective interest rate on the Company’s 2024 Term Loan B from LIBOR plus 2.50% to LIBOR plus 2.00% (subject to a 0.00% LIBOR floor in both instances). All other key terms associated with the 2024 Term Loan B remained consistent with the terms that existed following the September 2017 refinancing of the Senior Credit Facility (refer to the Annual Report for further information). As a result of this repricing, during the nine months ended September 30, 2018, the Company recognized a $0.2 million loss on extinguishment of long-term debt, comprised entirely of the write-off of a portion of the existing unamortized deferred financing fees related to the 2024 Term Loan B. Fees incurred in connection with the repricing of the 2024 Term Loan B were $1.1 million, of which $0.5 million were expensed and included within “Other expense (income), net” in the condensed consolidated statement of operations for the nine months ended September 30, 2018. The remaining $0.6 million of fees were capitalized and recorded within “Long-term debt, net of unamortized deferred financing fees” on the condensed consolidated balance sheet, to be amortized along with the remaining $16.4 million of unamortized deferred financing fees related to the 2024 Term Loan B. Capitalized fees related to the 2024 Term Loan B continue to be amortized over the remainder of the original 7.0 year term of the facility using the effective interest method. 2017 Debt Refinancing During the three and nine months ended September 30, 2017, the Company executed a refinancing of its debt. This included issuing $500.0 million aggregate principal amount of 5.375% 2025 Senior Notes as well as entering into a new Senior Credit Facility, which consists of the $375.0 million 2022 Revolving Facility and the $700.0 million 2024 Term Loan B, bearing an interest rate of LIBOR plus 2.50% (prior to the 2018 repricing mentioned above), subject to a 0.00% LIBOR floor. Using the net proceeds from the above along with available cash, the Company redeemed all outstanding indebtedness under its existing 2022 Senior Notes and repaid all outstanding borrowings under its existing 2020 Senior Credit Facility, together with a $53.0 million call premium on the 2022 Senior Notes, accrued and unpaid interest, and fees and other expenses related to the refinancing. As a result of the refinancing, the Company recorded a loss on extinguishment of long-term debt of $65.3 million during the three and nine months ended September 30, 2017. Refer to the Annual Report for further information.

Goodwill

Goodwill	9 Months Ended
	Sep. 30, 2018
Goodwill.
Goodwill	NOTE 7—GOODWILL The following table shows changes in the carrying amount of goodwill, by segment, from December 31, 2017 to September 30, 2018. Prior period balances in this table have been recast in conjunction with the segment realignment that occurred during the first quarter of 2018. Refer to Note 15 for further information. Latex Synthetic Performance Americas Binders Rubber Plastics Polystyrene Feedstocks Styrenics Total Balance at December 31, 2017 $ 16.5 $ 11.7 $ 39.6 $ 4.7 $ — $ — $ 72.5 Foreign currency impact (0.4) (0.3) (1.8) (0.1) — — (2.6) Balance at September 30, 2018 $ 16.1 $ 11.4 $ 37.8 $ 4.6 $ — $ — $ 69.9

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2018
Derivative Instruments [Abstract]
Derivative Instruments	NOTE 8—DERIVATIVE INSTRUMENTS The Company’s ongoing business operations expose it to various risks, including fluctuating foreign exchange rates and interest rate risk. To manage these risks, the Company periodically enters into derivative financial instruments, such as foreign exchange forward contracts and interest rate swap agreements. The Company does not hold or enter into financial instruments for trading or speculative purposes. All derivatives are recorded on the condensed consolidated balance sheets at fair value. As discussed in Note 2, the Company adopted new hedge accounting guidance effective April 1, 2018. The impacts of this adoption are discussed further below. Foreign Exchange Forward Contracts Certain subsidiaries have assets and liabilities denominated in currencies other than their respective functional currencies, which creates foreign exchange risk. The Company’s principal strategy in managing its exposure to changes in foreign currency exchange rates is to naturally hedge the foreign currency-denominated liabilities on its balance sheet against corresponding assets of the same currency such that any changes in liabilities due to fluctuations in exchange rates are offset by changes in their corresponding foreign currency assets. In order to further reduce this exposure, the Company also uses foreign exchange forward contracts to economically hedge the impact of the variability in exchange rates on assets and liabilities denominated in certain foreign currencies. These derivative contracts are not designated for hedge accounting treatment. As of September 30, 2018, the Company had open foreign exchange forward contracts with a notional U.S. dollar equivalent absolute value of $487.1 million. The following table displays the notional amounts of the most significant net foreign exchange hedge positions outstanding as of September 30, 2018: September 30, Buy / (Sell) 2018 Euro $ (301.1) Chinese Yuan $ (54.1) Swiss Franc $ 51.4 Mexican Peso $ (13.1) Indonesian Rupiah $ (11.5) Open foreign exchange forward contracts as of September 30, 2018 had maturities occurring over a period of two months. Foreign Exchange Cash Flow Hedges The Company also enters into forward contracts with the objective of managing the currency risk associated with forecasted U.S. dollar-denominated raw materials purchases by one of its subsidiaries whose functional currency is the euro. By entering into these forward contracts, which are designated as cash flow hedges, the Company buys a designated amount of U.S. dollars and sells euros at the prevailing market rate to mitigate the risk associated with the fluctuations in the euro-to-U.S. dollar foreign currency exchange rates. The qualifying hedge contracts are marked-to-market at each reporting date and any unrealized gains or losses are included in AOCI to the extent effective, and reclassified to cost of sales in the period during which the transaction affects earnings or it becomes probable that the forecasted transaction will not occur. Open foreign exchange cash flow hedges as of September 30, 2018 had maturities occurring over a period of fifteen months, and had a net notional U.S. dollar equivalent of $124.8 million. Interest Rate Swaps On September 6, 2017, the Company issued the 2024 Term Loan B, which currently bears an interest rate of LIBOR plus 2.00%, subject to a 0.00% LIBOR floor. In order to reduce the variability in interest payments associated with the Company’s variable rate debt, during the third quarter of 2017, the Company entered into certain interest rate swap agreements to convert a portion of these variable rate borrowings into a fixed rate obligation. These interest rate swap agreements are designated as cash flow hedges, and as such, the contracts are marked-to-market at each reporting date and any unrealized gains or losses are included in AOCI to the extent effective, and reclassified to interest expense in the period during which the transaction affects earnings or it becomes probable that the forecasted transaction will not occur. As of September 30, 2018, the Company had open interest rate swap agreements with a net notional U.S. dollar equivalent of $200.0 million which had an effective date of September 29, 2017 and mature over a period of five years. Under the terms of the swap agreements, the Company is required to pay the counterparties a stream of fixed interest payments at a rate of 1.81%, and in turn, receives variable interest payments based on 1-month LIBOR (2.24% as of September 30, 2018) from the counterparties. Net Investment Hedge Through August 31, 2017, the Company had designated a portion ( €280.0 million) of the original principal amount of the Company’s previous €375.0 million Euro Notes as a hedge of the foreign currency exposure of the Issuers’ net investment in certain European subsidiaries. Effective September 1, 2017, the Company de-designated the Euro Notes as a net investment hedge of the Issuers’ net investment in certain European subsidiaries, as the Euro Notes were redeemed on September 7, 2017. Through the date of de-designation, this hedge was deemed to be highly effective, and changes in the Euro Notes’ carrying value resulting from fluctuations in the euro exchange rate were recorded as cumulative foreign currency translation loss of $24.1 million within AOCI as of December 31, 2017. On August 29, 2017, the Issuers executed an indenture pursuant to which they issued the $500.0 million 5.375% 2025 Senior Notes. Subsequently, on September 1, 2017, the Company entered into certain fixed-for-fixed cross currency swaps (“CCS”), swapping USD principal and interest payments on the newly issued 2025 Senior Notes for euro-denominated payments . Under the terms of the CCS, the Company has notionally exchanged $500.0 million at an interest rate of 5.375% for €420.0 million at a weighted average interest rate of 3.45% for approximately five years. On September 1, 2017, the Company designated the full notional amount of the CCS (€420 million) as a hedge of the Issuers’ net investment in certain European subsidiaries under the forward method, with all changes in the fair value of the CCS recorded as a component of AOCI, as the CCS were deemed to be highly effective hedges. A cumulative foreign currency translation loss of $38.0 million was recorded within AOCI related to the CCS through March 31, 2018. Effective April 1, 2018, in conjunction with the adoption of recently issued hedging accounting guidance (see Note 2 for further information), the Company elected as an accounting policy to re-designate the CCS as a net investment hedge (and any future similar hedges) under the spot method. As such, changes in the fair value of the CCS that are included in the assessment of effectiveness (changes due to spot foreign exchange rates) are recorded as cumulative foreign currency translation within OCI, and will remain in AOCI until either the sale or substantially complete liquidation of the subsidiary. As of September 30, 2018, no gains or losses have been reclassified from AOCI into income related to the sale or substantially complete liquidation of the relevant subsidiaries. As an additional accounting policy election applied to similar hedges under this new standard, the initial value of any component excluded from the assessment of effectiveness is recognized in income using a systematic and rational method over the life of the hedging instrument. Any difference between the change in the fair value of the excluded component and amounts recognized in income under that systematic and rational method is recognized in AOCI. Prior to the adoption of the new hedging accounting guidance on April 1, 2018, no components were excluded from the assessment of effectiveness for any of the Company’s existing net investment hedges. As of April 1, 2018, the initial excluded component value related to the CCS was $23.6 million, which the Company has elected to amortize as a reduction of “Interest expense, net” in the condensed consolidated statements of operations using the straight-line method over the remaining term of the CCS. Additionally, the accrual of periodic USD and euro-denominated interest receipts and payments under the terms of the CCS will also be recognized within “Interest expense, net” in the condensed consolidated statements of operations. Summary of Derivative Instruments The following tables present the effect of the Company’s derivative instruments, including those not designated for hedge accounting treatment, on the condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017: Location and Amount of Gain (Loss) Recognized in Three Months Ended Three Months Ended September 30, 2018 September 30, 2017 Cost of Interest expense, net Other expense (income), net Cost of Interest expense, net Other expense (income), net Total amounts of income and expense line items presented in the statements of operations in which the effects of derivative instruments are recorded $ 1,068.1 $ 10.1 $ 2.1 $ 948.1 $ 18.4 $ 2.1 The effects of cash flow hedge instruments: Foreign exchange cash flow hedges Amount of loss reclassified from AOCI into income $ (0.6) $ — $ — $ (2.7) $ — $ — Interest rate swaps Amount of gain reclassified from AOCI into income $ — $ 0.1 $ — $ — $ — $ — The effects of net investment hedge instruments: Cross currency swaps (CCS) Amount of gain excluded from effectiveness testing $ — $ 3.8 $ — $ — $ — $ — The effects of derivatives not designated as hedge instruments: Foreign exchange forward contracts Amount of gain (loss) recognized in income $ — $ — $ 8.2 $ — $ — $ (6.5) Location and Amount of Gain (Loss) Recognized in Nine Months Ended Nine Months Ended September 30, 2018 September 30, 2017 Cost of Interest expense, net Other expense (income), net Cost of Interest expense, net Other expense (income), net Total amounts of income and expense line items presented in the statements of operations in which the effects of derivative instruments are recorded $ 3,088.3 $ 35.8 $ 2.9 $ 2,872.3 $ 55.4 $ (0.1) The effects of cash flow hedge instruments: Foreign exchange cash flow hedges Amount of gain (loss) reclassified from AOCI into income $ (6.8) $ — $ — $ 0.8 $ — $ — Interest rate swaps Amount of gain reclassified from AOCI into income $ — $ 0.1 $ — $ — $ — $ — The effects of net investment hedge instruments: Cross currency swaps (CCS) Amount of gain excluded from effectiveness testing $ — $ 7.7 $ — $ — $ — $ — The effects of derivatives not designated as hedge instruments: Foreign exchange forward contracts Amount of gain (loss) recognized in income $ — $ — $ 17.0 $ — $ — $ (17.0) The following table presents the effect of cash flow and net investment hedge accounting on AOCI for the three and nine months ended September 30, 2018 and 2017: Gain (Loss) Recognized in AOCI on Balance Sheet Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Designated as Cash Flow Hedges Foreign exchange cash flow hedges $ 1.2 $ (4.5) $ 11.3 $ (22.2) Interest rate swaps 0.9 0.8 5.5 0.7 Total $ 2.1 $ (3.7) $ 16.8 $ (21.5) Designated as Net Investment Hedges Euro Notes $ — $ (13.9) $ — $ (38.6) Cross currency swaps (CCS) (0.6) (7.1) 9.7 (7.1) Total $ (0.6) $ (21.0) $ 9.7 $ (45.7) The Company recorded gains of $8.2 million and $17.0 million during the three and nine months ended September 30, 2018, respectively, and losses of $6.5 million and $17.0 million during the three and nine months ended September 30, 2017, respectively, from settlements and changes in the fair value of outstanding forward contracts (not designated as hedges) . The gains and losses from these forward contracts offset net foreign exchange transaction losses of $6.9 million and $12.6 million during the three and nine months ended September 30, 2018, respectively, and gains of $8.2 million and $16.1 million during the three and nine months ended September 30, 2017, respectively, which resulted from the remeasurement of the Company’s foreign currency denominated assets and liabilities. The cash settlements of these foreign exchange forward contracts are included within operating activities in the condensed consolidated statements of cash flows. The Company expects to reclassify in the next twelve months an approximate $1.6 million net gain from AOCI into earnings related to the Company’s outstanding foreign exchange cash flow hedges and interest rate swaps as of September 30, 2018 based on current foreign exchange rates. The following tables summarize the gross and net unrealized gains and losses, as well as the balance sheet classification, of outstanding derivatives recorded in the condensed consolidated balance sheets: September 30, 2018 Foreign Foreign Exchange Exchange Interest Cross Balance Sheet Forward Cash Flow Rate Currency Classification Contracts Hedges Swaps Swaps Total Asset Derivatives: Accounts receivable, net of allowance $ 4.4 $ 0.9 $ 1.6 $ 5.7 $ 12.6 Deferred charges and other assets — — 6.8 — 6.8 Gross derivative asset position 4.4 0.9 8.4 5.7 19.4 Less: Counterparty netting (0.8) (0.2) — — (1.0) Net derivative asset position $ 3.6 $ 0.7 $ 8.4 $ 5.7 $ 18.4 Liability Derivatives: Accounts payable $ (1.4) $ (0.9) $ — $ — $ (2.3) Other noncurrent obligations — — — (16.2) (16.2) Gross derivative liability position (1.4) (0.9) — (16.2) (18.5) Less: Counterparty netting 0.8 0.2 — — 1.0 Net derivative liability position $ (0.6) $ (0.7) $ — $ (16.2) $ (17.5) Total net derivative position $ 3.0 $ — $ 8.4 $ (10.5) $ 0.9 December 31, 2017 Foreign Foreign Exchange Exchange Interest Cross Balance Sheet Forward Cash Flow Rate Currency Classification Contracts Hedges Swaps Swaps Total Asset Derivatives: Accounts receivable, net of allowance $ 0.7 $ — $ — $ 10.8 $ 11.5 Deferred charges and other assets — — 3.0 — 3.0 Gross derivative asset position 0.7 — 3.0 10.8 14.5 Less: Counterparty netting (0.6) — — — (0.6) Net derivative asset position $ 0.1 $ — $ 3.0 $ 10.8 $ 13.9 Liability Derivatives: Accounts payable $ (3.1) $ (11.1) $ (0.1) $ — $ (14.3) Other noncurrent obligations — — — (28.3) (28.3) Gross derivative liability position (3.1) (11.1) (0.1) (28.3) (42.6) Less: Counterparty netting 0.6 — — — 0.6 Net derivative liability position $ (2.5) $ (11.1) $ (0.1) $ (28.3) $ (42.0) Total net derivative position $ (2.4) $ (11.1) $ 2.9 $ (17.5) $ (28.1) Forward contracts, interest rate swaps, and cross currency swaps are entered into with a limited number of counterparties, each of which allows for net settlement of all contracts through a single payment in a single currency in the event of a default on or termination of any one contract. As such, in accordance with the Company’s accounting policy, these derivative instruments are recorded on a net basis by counterparty within the condensed consolidated balance sheets. Refer to Notes 9 and 17 of the condensed consolidated financial statements for further information regarding the fair value of the Company’s derivative instruments and the related changes in AOCI .

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Measurements
Fair Value Measurements	NOTE 9—FAIR VALUE MEASUREMENTS Fair value is defined as 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. Assets and liabilities measured at fair value are classified using the following hierarchy, which is based upon the transparency of inputs to the valuation as of the measurement date. Level 1—Valuation is based upon quoted prices (unadjusted) for identical assets or liabilities in active markets. Level 2—Valuation is based upon quoted prices for similar assets and liabilities in active markets, or other inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. Level 3—Valuation is based upon other unobservable inputs that are significant to the fair value measurement. The following table summarizes the basis used to measure certain assets and liabilities at fair value on a recurring basis in the condensed consolidated balance sheets as of September 30, 2018 and December 31, 2017: September 30, 2018 Quoted Prices in Active Markets for Identical Items Significant Other Observable Inputs Significant Unobservable Inputs Assets (Liabilities) at Fair Value (Level 1) (Level 2) (Level 3) Total Foreign exchange forward contracts—Assets $ — $ 3.6 $ — $ 3.6 Foreign exchange forward contracts—(Liabilities) — (0.6) — (0.6) Foreign exchange cash flow hedges—Assets — 0.7 — 0.7 Foreign exchange cash flow hedges—(Liabilities) — (0.7) — (0.7) Interest rate swaps—Assets — 8.4 — 8.4 Cross currency swaps—Assets — 5.7 — 5.7 Cross currency swaps—(Liabilities) — (16.2) — (16.2) Total fair value $ — $ 0.9 $ — $ 0.9 December 31, 2017 Quoted Prices in Active Markets for Identical Items Significant Other Observable Inputs Significant Unobservable Inputs Assets (Liabilities) at Fair Value (Level 1) (Level 2) (Level 3) Total Foreign exchange forward contracts—Assets $ — $ 0.1 $ — $ 0.1 Foreign exchange forward contracts—(Liabilities) — (2.5) — (2.5) Foreign exchange cash flow hedges—(Liabilities) — (11.1) — (11.1) Interest rate swaps—Assets — 3.0 — 3.0 Interest rate swaps—(Liabilities) — (0.1) — (0.1) Cross currency swaps—Assets — 10.8 — 10.8 Cross currency swaps—(Liabilities) — (28.3) — (28.3) Total fair value $ — $ (28.1) $ — $ (28.1) The Company uses an income approach to value its derivative instruments, utilizing discounted cash flow techniques, considering the terms of the contract and observable market information available as of the reporting date, such as interest rate yield curves and currency spot and forward rates. Significant inputs to the valuation for these derivative instruments are obtained from broker quotations or from listed or over-the-counter market data, and are classified as Level 2 in the fair value hierarchy. Fair Value of Debt Instruments The following table presents the estimated fair value of the Company’s outstanding debt not carried at fair value as of September 30, 2018 and December 31, 2017, respectively: As of As of September 30, 2018 December 31, 2017 2025 Senior Notes $ 483.3 $ 518.8 2024 Term Loan B 694.3 705.7 Total fair value $ 1,177.6 $ 1,224.5 The fair value of the Company’s debt facilities above (each Level 2 securities) is determined using over-the-counter market quotes and benchmark yields received from independent vendors. There were no other significant financial instruments outstanding as of September 30, 2018 and December 31, 2017.

Provision for Income Taxes

Provision for Income Taxes	9 Months Ended
	Sep. 30, 2018
Provision for Income Taxes
Income Taxes	NOTE 10—PROVISION FOR INCOME TAXES Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Effective income tax rate 20.5 % 20.0 % 18.0 % 21.1 % Provision for income taxes for the three and nine months ended September 30, 2018 were $19.2 million, resulting in an effective tax rate of 20.5%, and $64.5 million, resulting in an effective tax rate of 18.0%, respectively. Provision for income taxes for the three and nine months ended September 30, 2017 were $8.3 million, resulting in an effective tax rate of 20%, and $56.4 million, resulting in an effective tax rate of 21.1%, respectively. The effective tax rate for the three and nine months ended September 30, 2018 was impacted by the reduction in the U.S. federal corporate tax rate from 35% to 21%, effective January 1, 2018, in accordance with the enactment of the “Tax Cuts and Jobs Act” signed into law on December 22, 2017. The effective tax rate for these periods was also impacted by a lower proportion of income before taxes attributable to non-U.S. jurisdictions, where the statutory income tax rate is lower than the U.S. statutory income tax rate, as compared to the same periods in 2017. The effective tax rate for the three and nine months ended September 30, 2017 was impacted by payments made of $10.9 million for the period ended September 30, 2017 related to a portion of the fees associated with the call premium paid to retire the Company’s 2022 Senior Notes, which are not anticipated to provide a tax benefit to the Company in the future. Additionally, the nine months ended September 30, 2017 was impacted by the $9.3 million gain on sale of the Company’s 50% share in Sumika Styron Polycarbonate during the nine months ended September 30, 2017, which was exempt from tax.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure
Commitments and Contingencies	NOTE 11—COMMITMENTS AND CONTINGENCIES Environmental Matters Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law, existing technologies and other information. Pursuant to the terms of the agreement associated with the Company’s formation, the pre-closing environmental conditions were retained by Dow, and Dow has agreed to indemnify the Company from and against all environmental liabilities incurred or relating to the predecessor periods. No environmental claims have been asserted or threatened against the Company, and the Company is not a potentially responsible party at any Superfund Sites. As of September 30, 2018 and December 31, 2017, the Company had no accrued obligations for environmental remediation or restoration costs. Inherent uncertainties exist in the Company’s potential environmental liabilities primarily due to unknown conditions, whether future claims may fall outside the scope of the indemnity, changing governmental regulations and legal standards regarding liability, and evolving technologies for handling site remediation and restoration. In connection with the Company’s existing indemnification, the possibility is considered remote that environmental remediation costs will have a material adverse impact on the condensed consolidated financial statements. Purchase Commitments In the normal course of business, the Company has certain raw material purchase contracts where it is required to purchase certain minimum volumes at current market prices. These commitments range from 1 to 4 years. In certain raw material purchase contracts, the Company has the right to purchase less than the required minimums and pay a liquidated damages fee, or, in case of a permanent plant shutdown, to terminate the contracts. In such cases, these obligations would be less than the annual commitment as disclosed in the Notes to Consolidated Financial Statements included in the Annual Report. Litigation Matters From time to time, the Company may be subject to various legal claims and proceedings incidental to the normal conduct of business, relating to such matters as employees, product liability, antitrust/competition, past waste disposal practices and release of chemicals into the environment. While it is impossible at this time to determine with certainty the ultimate outcome of these routine claims, the Company does not believe that the ultimate resolution of these claims will have a material adverse effect on the Company’s results of operations, financial condition or cash flow. Legal costs, including those legal costs expected to be incurred in connection with a loss contingency, are expensed as incurred. European Commission Request for Information On June 6, 2018, Trinseo Europe GmbH, a subsidiary of the Company, received a Request for Information in the form of a letter from the European Commission Directorate General for Competition (the “European Commission”) related to styrene monomer commercial activity in the European Economic Area. In addition, the Company commenced an internal investigation into the matter and has discovered instances of inappropriate activity. The Company is fully cooperating with the European Commission and has delivered all requested documents responsive to its information request. Notwithstanding the delivery of the Company’s response to the European Commission, this matter remains open with the European Commission. Based on its findings, the European Commission may decide to: (i) require further information; (ii) conduct unannounced raids of the Company’s premises; (iii) adopt decisions imposing fines, interim measures to halt immediately any anti-competitive behavior, orders for the Company to cease anti-competitive activities, and/or certain behavioral or structural commitments from the Company; or (iv) take no further action. As a result of the above factors, the Company is unable to predict the ultimate outcome of this matter or estimate the range of reasonably possible losses that could be incurred. However, any potential losses incurred could be material to the Company’s results of operations, balance sheet, and cash flows for the period in which they are resolved or become probable and reasonably estimable.

Pension Plans and Other Postret

Pension Plans and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2018
Pension Plans and Other Postretirement Benefits
Pension Plans and Other Postretirement Benefits	NOTE 12—PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS The components of net periodic benefit costs for all significant plans were as follows: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Defined Benefit Pension Plans Service cost $ 3.0 $ 5.0 $ 9.2 $ 14.3 Interest cost 1.2 1.2 3.7 3.4 Expected return on plan assets (0.5) (0.5) (1.6) (1.3) Amortization of prior service credit (0.3) (0.5) (0.9) (1.5) Amortization of net loss 0.8 1.5 2.7 4.3 Net settlement and curtailment loss (1) — — — 0.1 Net periodic benefit cost $ 4.2 $ 6.7 $ 13.1 $ 19.3 (1) Represents a settlement loss of approximately $0.5 million triggered by benefit payments exceeding the sum of service and interest cost for one of the Company’s pension plans in Switzerland, partially offset by a curtailment gain of approximately $0.4 million related to a reduction in the number of participants in the Company’s pension plan in Japan. Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Other Postretirement Plans Service cost $ — $ — $ 0.1 $ 0.1 Interest cost 0.1 0.1 0.2 0.2 Amortization of prior service cost — — 0.1 0.1 Amortization of net gain — — — — Net periodic benefit cost $ 0.1 $ 0.1 $ 0.4 $ 0.4 In accordance with recently issued accounting standards, service cost related to the Company’s defined benefit pension plans and other postretirement plans is included within “Cost of sales” and “Selling, general and administrative expenses” whereas all other components of net periodic benefit cost are included within “Other expense (income), net” in the condensed consolidated statements of operations. Refer to Note 2 for further information. As of September 30, 2018 and December 31, 2017, the Company’s benefit obligations included primarily in “Other noncurrent obligations” in the condensed consolidated balance sheets were $190.2 million and $188.7 million, respectively. The Company made cash contributions and benefit payments to unfunded plans of approximately $1.3 million and $4.4 million during the three and nine months ended September 30, 2018, respectively. The Company expects to make additional cash contributions, including benefit payments to unfunded plans, of approximately $1.9 million to its defined benefit plans for the remainder of 2018.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2018
Stock-Based Compensation
Stock-Based Compensation	NOTE 13—STOCK-BASED COMPENSATION Refer to the Annual Report for definitions of capitalized terms not included herein and further background on the Company’s stock-based compensation programs included in the tables below. The following table summarizes the Company’s stock-based compensation expense for the three and nine months ended September 30, 2018 and 2017, as well as unrecognized compensation cost as of September 30, 2018: As of Three Months Ended Nine Months Ended September 30, 2018 September 30, September 30, Unrecognized Weighted 2018 2017 2018 2017 Compensation Cost Average Years RSUs $ 2.3 $ 2.3 $ 6.6 $ 6.3 $ 12.4 2.0 Options 0.5 0.5 3.9 3.7 1.8 1.3 PSUs 0.6 0.3 1.8 0.8 6.6 2.3 Total stock-based compensation expense $ 3.4 $ 3.1 $ 12.3 $ 10.8 The following table summarizes awards granted and the respective weighted average grant date fair value for the nine months ended September 30, 2018: Nine Months Ended September 30, 2018 Awards Granted Weighted Average Grant Date Fair Value per Award RSUs 131,240 $ 79.18 Options 202,963 22.29 PSUs 70,301 86.78 Option Awards The following are the weighted average assumptions used within the Black-Scholes pricing model for the Company’s option awards granted during the nine months ended September 30, 2018: Nine Months Ended September 30, 2018 Expected term (in years) 5.50 Expected volatility 32.00 % Risk-free interest rate 2.71 % Dividend yield 2.00 % Since the Company’s equity interests were privately held prior to its initial public offering (“IPO”) in June 2014, there is limited publicly traded history of the Company’s ordinary shares. Until such time that the Company can determine expected volatility based solely on the publicly traded history of its ordinary shares, expected volatility used in the Black-Scholes model for option awards granted is based on a combination of the Company’s historical volatility and similar companies’ stock that are publicly traded. The expected term of option awards represents the period of time that option awards granted are expected to be outstanding. For the option awards granted during the nine months ended September 30, 2018, the simplified method was used to calculate the expected term, given the Company’s limited historical exercise data. The risk-free interest rate for the periods within the expected term of option awards is based on the U.S. Treasury yield curve in effect at the time of grant. The dividend yield is estimated based on historical and expected dividend activity. Performance Share Units (PSUs) The following are the weighted average assumptions used within the Monte Carlo valuation model for PSUs granted during the nine months ended September 30, 2018: Nine Months Ended September 30, 2018 Expected term (in years) 3.00 Expected volatility 35.03 % Risk-free interest rate 2.55 % Share Price $ 79.42 Determining the fair value of PSUs requires considerable judgment, including estimating the expected volatility of the price of the Company’s ordinary shares, the correlation between the Company’s share price and that of its peer companies, and the expected rate of interest. The expected volatility for each grant is determined based on the historical volatility of the Company’s ordinary shares. The expected term of PSUs represents the length of the performance period. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for a duration equivalent to the performance period. The share price is the closing price of the Company’s ordinary shares on the grant date.

Acquisitions and Divestitures

Acquisitions and Divestitures	9 Months Ended
	Sep. 30, 2018
Acquisitions and Divestitures
Acquisitions and Divestitures	NOTE 14—ACQUISITIONS AND DIVESTITURES Acquisition of API Plastics On July 10, 2017, the Company acquired 100% of the equity interests of API Applicazioni Plastiche Industriali S.p.A (“API Plastics”), a privately held company. The gross purchase price for the acquisition was $90.6 million, inclusive of $8.4 million of cash acquired, yielding a net purchase price of $82.3 million. During the nine months ended September 30, 2017, the Company paid $79.7 million for this acquisition, with an additional $2.6 million paid during the fourth quarter of 2017. API Plastics, based in Mussolente, Italy, is a manufacturer of soft-touch polymers and bioplastics, such as thermoplastic elastomers (“TPEs”), whose results are included within the Company’s Performance Plastics segment. The Company allocated the purchase price of the acquisition to identifiable assets acquired and liabilities assumed based on their estimated fair values as of the acquisition date. There were no changes made to the purchase price allocation during the nine months ended September 30, 2018. As of September 30, 2018, the acquisition measurement period for API Plastics has ended and the values assigned to the assets acquired and liabilities assumed are final. Transaction and integration costs related to advisory and professional fees incurred in conjunction with the API Plastics acquisition were $0.1 million and $0.6 million during the three and nine months ended September 30, 2018, respectively, compared to $2.4 and $3.5 million during the three and nine months ended September 30, 2017, respectively, and were included within “Selling, general and administrative expenses” in the condensed consolidated statements of operations. Refer to the Annual Report for further information.

Segments

Segments	9 Months Ended
	Sep. 30, 2018
Segments
Segments	NOTE 15—SEGMENTS Through December 31, 2017, the Company operated under two divisions: Performance Materials and Basic Plastics & Feedstocks. The Performance Materials division included the following reporting segments: Latex Binders, Synthetic Rubber, and Performance Plastics. The Basic Plastics & Feedstocks division included the following reporting segments: Basic Plastics, Feedstocks, and Americas Styrenics. Effective January 1, 2018, the Company realigned its reporting segments to reflect the new model under which the business will be managed and results will be reviewed by the chief executive officer, who is the Company’s chief operating decision maker. Under this new segmentation, the Company will no longer have divisions, but will continue to report operating results for six segments, four of which remain unchanged from the Company’s prior segmentation: Latex Binders, Synthetic Rubber, Feedstocks, and Americas Styrenics. The results of the Company’s Polystyrene business, which were previously included within the results of the Basic Plastics segment, are now reported as a stand-alone segment. Performance Plastics, which previously consisted of compounds, blends, and ABS products sold to the automotive market, now includes the remaining portion of the Company’s ABS business, as well as the results of the Company’s SAN and PC businesses. This segmentation change will provide enhanced clarity to investors by concentrating the Company’s more specialized plastics into a single reporting segment, while also reducing complexity as PC and ABS are the primary inputs into the downstream production of the Company’s compounds and blends. The information in the tables below has been retroactively adjusted to reflect the changes in reporting segments. The Latex Binders segment produces styrene-butadiene latex (“SB latex”) and other latex polymers and binders, primarily for coated paper and packaging board, carpet and artificial turf backings, as well as a number of performance latex binders applications, such as adhesive, building and construction and the technical textile paper market. The Synthetic Rubber segment produces synthetic rubber products used predominantly in high-performance tires, impact modifiers and technical rubber products, such as conveyer belts, hoses, seals and gaskets. The Performance Plastics segment produces highly engineered compounds and blends, and also includes the Company’s ABS, SAN, and PC businesses. The Performance Plastics segment, as recast, also included the results of the Company’s previously 50%-owned joint venture, Sumika Styron Polycarbonate, until the Company sold its share in the entity in January 2017 (refer to Note 4 for further information). Polystyrene is a stand-alone reporting segment, and includes a variety of general purpose polystyrenes (“GPPS”) and polystyrene that has been modified with polybutadiene rubber to increase its impact resistant properties (“HIPS”). The Feedstocks segment includes the Company’s production and procurement of styrene monomer outside of North America, which is used as a key raw material in many of the Company’s products, including polystyrene, SB latex, ABS resins, solution styrene-butadiene rubber (“SSBR”), etc. Lastly, the Americas Styrenics segment consists solely of the operations of the Company’s 50%-owned joint venture, Americas Styrenics, a producer of both styrene monomer and polystyrene in North America. Asset and intersegment sales information by reporting segment is not regularly reviewed or included with the Company’s reporting to the chief operating decision maker. Therefore, this information has not been disclosed below. Latex Synthetic Performance Americas Corporate Three Months Ended Binders Rubber Plastics Polystyrene Feedstocks Styrenics Unallocated Total September 30, 2018 Sales to external customers $ 278.0 $ 137.7 $ 400.7 $ 252.3 $ 131.0 $ — $ — $ 1,199.7 Equity in earnings of unconsolidated affiliates — — — — — 34.5 — 34.5 Adjusted EBITDA (1) 24.7 15.5 43.8 5.0 40.3 34.5 Investment in unconsolidated affiliates — — — — — 180.8 — 180.8 Depreciation and amortization 6.2 10.6 6.9 2.9 2.9 — 2.3 31.8 September 30, 2017 Sales to external customers $ 266.3 $ 118.7 $ 362.2 $ 238.4 $ 111.0 $ — $ — $ 1,096.6 Equity in earnings of unconsolidated affiliates — — — — — 43.8 — 43.8 Adjusted EBITDA (1) 32.3 (5.6) 62.4 9.1 45.6 43.8 Investment in unconsolidated affiliates — — — — — 161.9 — 161.9 Depreciation and amortization 6.0 9.0 5.3 3.1 3.6 — 2.2 29.2 Latex Synthetic Performance Americas Corporate Nine Months Ended Binders Rubber Plastics Polystyrene Feedstocks Styrenics Unallocated Total September 30, 2018 Sales to external customers $ 814.2 $ 442.2 $ 1,216.2 $ 777.5 $ 307.7 $ — $ — $ 3,557.8 Equity in earnings of unconsolidated affiliates — — — — — 113.3 — 113.3 Adjusted EBITDA (1) 88.2 71.6 158.2 28.0 114.3 113.3 Investment in unconsolidated affiliates — — — — — 180.8 — 180.8 Depreciation and amortization 18.6 33.1 20.0 8.6 8.9 — 6.8 96.0 September 30, 2017 Sales to external customers $ 846.7 $ 456.1 $ 1,038.4 $ 700.2 $ 304.9 $ — $ — $ 3,346.3 Equity in earnings of unconsolidated affiliates — — 0.8 — — 92.2 — 93.0 Adjusted EBITDA (1) 105.2 68.4 162.9 29.6 86.3 92.2 Investment in unconsolidated affiliates — — — — — 161.9 — 161.9 Depreciation and amortization 17.5 26.0 13.7 7.3 9.2 — 6.4 80.1 (1) The reconciliation of income before income taxes to Segment Adjusted EBITDA is as follows: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Income before income taxes $ 93.9 $ 41.5 $ 357.8 $ 267.1 Interest expense, net 10.1 18.4 35.8 55.4 Depreciation and amortization 31.8 29.2 96.0 80.1 Corporate Unallocated (2) 20.9 21.8 65.6 70.8 Adjusted EBITDA Addbacks (3) 7.1 76.7 18.4 71.2 Segment Adjusted EBITDA $ 163.8 $ 187.6 $ 573.6 $ 544.6 (2) (3) Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Loss on extinguishment of long-term debt (Note 6) $ — $ 65.3 $ 0.2 $ 65.3 Net loss (gain) on disposition of businesses and assets (Note 4) — 0.2 (0.5) (9.7) Restructuring and other charges (Note 16) 0.9 1.5 2.6 4.8 Acquisition transaction and integration costs (Note 14) 0.1 3.8 0.6 4.9 Asset impairment charges or write-offs (a) — 4.3 — 4.3 Other items (b) 6.1 1.6 15.5 1.6 Total Adjusted EBITDA Addbacks $ 7.1 $ 76.7 $ 18.4 $ 71.2 (a) Asset impairment charges for the three and nine months ended September 30, 2017 primarily relate to the impairment of certain long-lived assets in the Company’s Performance Plastics segment. (b) Other items for the three and nine months ended September 30, 2018 primarily relate to advisory and professional fees incurred in conjunction with the Company’s initiative to transition business services from Dow, including certain administrative services such as accounts payable, logistics, and IT services. Also included within other items for the nine months ended September 30, 2018 are fees incurred in conjunction with the Company’s 2024 Term Loan B repricing which was completed during the second quarter of 2018. Other items for the three and nine months ended September 30, 2017 primarily relate to fees incurred in conjunction with the Company’s debt refinancing which was completed during the third quarter of 2017.

Restructuring

Restructuring	9 Months Ended
	Sep. 30, 2018
Restructuring
Restructuring	NOTE 16—RESTRUCTURING Refer to the Annual Report for further details regarding the Company’s previously announced restructuring activities included in the tables below. Restructuring charges are included within “Selling, general and administrative expenses” in the condensed consolidated statements of operations. The following table provides detail of the Company’s restructuring charges for the three and nine months ended September 30, 2018 and 2017: Three Months Ended Nine Months Ended Cumulative September 30, September 30, Life-to-date 2018 2017 2018 2017 Charges Segment Terneuzen Compounding Restructuring (1) Asset impairment/accelerated depreciation $ 0.3 $ 0.6 $ 0.8 $ 1.7 $ 2.9 Employee termination benefits 0.1 0.2 0.5 0.3 0.9 Contract terminations — — — 0.6 0.6 Decommissioning and other 0.3 0.2 0.5 0.2 1.3 Terneuzen Subtotal $ 0.7 $ 1.0 $ 1.8 $ 2.8 $ 5.7 Performance Plastics Livorno Plant Restructuring (2) Asset impairment/accelerated depreciation $ — $ — $ 0.4 $ — $ 14.7 Employee termination benefits — 0.2 — 0.6 5.4 Contract terminations — — — — 0.3 Decommissioning and other 0.2 0.6 0.6 1.7 3.6 Livorno Subtotal $ 0.2 $ 0.8 $ 1.0 $ 2.3 $ 24.0 Latex Binders Other Restructurings 0.3 0.3 0.7 1.5 Various Total Restructuring Charges $ 1.2 $ 2.1 $ 3.5 $ 6.6 (1) In March 2017, the Company announced plans to upgrade its production capability for compounded resins with the construction of a new state-of-the art compounding facility to replace its existing compounding facility in Terneuzen, The Netherlands. The new facility is expected to be operational by the end of 2018 with ongoing customer qualifications into early 2019. Further, substantive production at the existing facility is expected to cease during the first half of 2019, followed by decommissioning activities in 2019 and 2020. The Company expects to incur incremental accelerated depreciation charges of approximately $0.3 million through the end of 2018, as well as decommissioning and other charges of approximately $0.6 million throughout 2019, the majority of which are expected to be paid throughout 2019. (2) In August 2016, the Company announced its plan to cease manufacturing activities at its latex binders manufacturing facility in Livorno, Italy. Production at the facility ceased in October 2016 and decommissioning activities began in the fourth quarter of 2016. In June 2018, the Company entered into a preliminary agreement to sell the land where the former facility is located, subject to certain activities being completed prior to closing. In conjunction with the execution of this agreement, the Company received approximately $1.3 million of the purchase price as a prepayment, which has been deferred and recorded within “Accrued expenses and other current liabilities” on the condensed consolidated balance sheet as of September 30, 2018. The Company expects to record an immaterial gain on sale when the transaction is completed. Furthermore, as this sale is considered probable within one year of the balance sheet date, the Company recorded the $12.2 million of land as held-for-sale within “Other current assets”, as well as a deferred tax liability associated with that land of $2.9 million as held-for-sale within “Accrued expenses and other current liabilities”, on the condensed consolidated balance sheet as of September 30, 2018. The Company will continue to incur additional decommissioning costs associated with this plant shutdown through the closing date of the sale, the cost of which will be expensed as incurred. The following table provides a roll forward of the liability balances associated with the Company’s restructuring activities as of September 30, 2018. Employee termination benefit and contract termination charges are recorded within “Accrued expenses and other current liabilities” in the condensed consolidated balance sheets. Balance at Balance at December 31, 2017 Expenses Deductions (1) September 30, 2018 Employee termination benefits $ 1.4 $ 0.5 $ (0.9) $ 1.0 Contract terminations 0.6 — — 0.6 Decommissioning and other — 1.8 (1.8) — Total $ 2.0 $ 2.3 $ (2.7) $ 1.6 (1) Primarily includes payments made against the existing accrual, as well as immaterial impacts of foreign currency remeasurement. .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2018
Shareholders' Equity.
Accumulated Other Comprehensive Income (Loss)	NOTE 17—ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The components of AOCI, net of income taxes, consisted of: Cumulative Pension & Other Translation Postretirement Benefit Cash Flow Three Months Ended September 30, 2018 and 2017 Adjustments Plans, Net Hedges, Net Total Balance as of June 30, 2018 $ (112.7) $ (43.8) $ 8.6 $ (147.9) Other comprehensive income (loss) (4.6) — 1.6 (3.0) Amounts reclassified from AOCI to net income (1) — 0.6 0.5 1.1 Balance as of September 30, 2018 $ (117.3) $ (43.2) $ 10.7 $ (149.8) Balance as of June 30, 2017 $ (95.8) $ (61.3) $ (5.5) $ (162.6) Other comprehensive loss (1.6) — (6.4) (8.0) Amounts reclassified from AOCI to net income (1) — 0.8 2.7 3.5 Balance as of September 30, 2017 $ (97.4) $ (60.5) $ (9.2) $ (167.1) Cumulative Pension & Other Translation Postretirement Benefit Cash Flow Nine Months Ended September 30, 2018 and 2017 Adjustments Plans, Net Hedges, Net Total Balance at December 31, 2017 $ (94.5) $ (45.0) $ (6.1) $ (145.6) Other comprehensive income (loss) (22.8) — 10.1 (12.7) Amounts reclassified from AOCI to net income (1) — 1.8 6.7 8.5 Balance at September 30, 2018 $ (117.3) $ (43.2) $ 10.7 $ (149.8) Balance as of December 31, 2016 $ (119.0) $ (63.5) $ 12.3 $ (170.2) Other comprehensive income (loss) 21.6 — (20.7) 0.9 Amounts reclassified from AOCI to net income (1) — 3.0 (0.8) 2.2 Balance as of September 30, 2017 $ (97.4) $ (60.5) $ (9.2) $ (167.1) (1) The following is a summary of amounts reclassified from AOCI to net income for the three and nine months ended September 30, 2018 and 2017: Amount Reclassified from AOCI Amount Reclassified from AOCI AOCI Components Three Months Ended September 30, Nine Months Ended September 30, Statements of Operations 2018 2017 2018 2017 Classification Cash flow hedging items Foreign exchange cash flow hedges $ 0.6 $ 2.7 $ 6.8 $ (0.8) Cost of sales Interest rate swaps (0.1) — (0.1) — Interest expense, net Total before tax 0.5 2.7 6.7 (0.8) Tax effect — — — — Provision for income taxes Total, net of tax $ 0.5 $ 2.7 $ 6.7 $ (0.8) Amortization of pension and other postretirement benefit plan items Prior service credit $ (0.2) $ (0.5) $ (0.7) $ (1.4) (a) Net actuarial loss 1.0 1.7 3.2 4.9 (a) Net settlement and curtailment loss — — — 0.6 (a) Total before tax 0.8 1.2 2.5 4.1 Tax effect (0.2) (0.4) (0.7) (1.1) Provision for income taxes Total, net of tax $ 0.6 $ 0.8 $ 1.8 $ 3.0 (a) These AOCI components are included in the computation of net periodic benefit costs (see Note 12). .

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share
Earnings Per Share	NOTE 18—EARNINGS PER SHARE Basic earnings per ordinary share (“basic EPS”) is computed by dividing net income available to ordinary shareholders by the weighted average number of the Company’s ordinary shares outstanding for the applicable period. Diluted earnings per ordinary share (“diluted EPS”) is calculated using net income available to ordinary shareholders divided by diluted weighted average ordinary shares outstanding during each period, which includes unvested RSUs, option awards, and PSUs. Diluted EPS considers the impact of potentially dilutive securities except in periods in which there is a loss because the inclusion of the potential ordinary shares would have an anti-dilutive effect. The following table presents basic EPS and diluted EPS for the three and nine months ended September 30, 2018 and 2017: Three Months Ended Nine Months Ended September 30, September 30, (in millions, except per share data) 2018 2017 2018 2017 Earnings: Net income $ 74.7 $ 33.2 $ 293.3 $ 210.7 Shares: Weighted average ordinary shares outstanding 42.6 43.7 43.0 43.9 Dilutive effect of RSUs, option awards, and PSUs (1) 0.7 1.1 0.9 1.1 Diluted weighted average ordinary shares outstanding 43.3 44.8 43.9 45.0 Income per share: Income per share—basic $ 1.75 $ 0.76 $ 6.82 $ 4.80 Income per share—diluted $ 1.72 $ 0.74 $ 6.68 $ 4.68 (1)

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2018
Basis of Presentation.
Basis of Presentation	The unaudited interim condensed consolidated financial statements of Trinseo S.A. and its subsidiaries (the “Company”) as of and for the periods ended September 30, 2018 and 2017 were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and reflect all adjustments, consisting only of normal recurring adjustments, which, in the opinion of management, are considered necessary for the fair statement of the results for the periods presented. Because they cover interim periods, the statements and related notes to the financial statements do not include all disclosures normally provided in annual financial statements, and therefore, these statements should be read in conjunction with the 2017 audited consolidated financial statements included within the Company’s Annual Report on Form 10-K (“Annual Report”) filed with the Securities and Exchange Commission (“SEC”) on March 1, 2018. The December 31, 2017 condensed consolidated balance sheet data presented herein was derived from the Company’s December 31, 2017 audited consolidated financial statements, but does not include all disclosures required by GAAP for annual periods. Certain prior year amounts have been reclassified to conform to the current period presentation. These reclassifications did not have a material impact on the Company’s financial position or results. Refer to Notes 2, 7, and 15 for further information.

Net Sales (Tables)

Net Sales (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	Latex Synthetic Performance Three Months Ended Binders Rubber Plastics Polystyrene Feedstocks Total September 30, 2018 United States $ 77.3 $ — $ 87.0 $ — $ 3.0 $ 167.3 Europe 117.0 137.7 226.7 148.3 61.2 690.9 Asia-Pacific 80.0 — 62.7 104.0 66.8 313.5 Rest of World 3.7 — 24.3 — — 28.0 Total $ 278.0 $ 137.7 $ 400.7 $ 252.3 $ 131.0 $ 1,199.7 September 30, 2017 (1) United States $ 73.7 $ — $ 76.8 $ 0.1 $ 3.5 $ 154.1 Europe 113.0 118.7 223.6 144.9 61.8 662.0 Asia-Pacific 75.3 — 39.1 93.4 45.7 253.5 Rest of World 4.3 — 22.7 — — 27.0 Total $ 266.3 $ 118.7 $ 362.2 $ 238.4 $ 111.0 $ 1,096.6 Latex Synthetic Performance Nine Months Ended Binders Rubber Plastics Polystyrene Feedstocks Total September 30, 2018 United States $ 216.3 $ — $ 253.7 $ 0.2 $ 9.6 $ 479.8 Europe 349.6 442.2 720.9 460.9 174.5 2,148.1 Asia-Pacific 236.9 — 171.0 316.4 123.6 847.9 Rest of World 11.4 — 70.6 — — 82.0 Total $ 814.2 $ 442.2 $ 1,216.2 $ 777.5 $ 307.7 $ 3,557.8 September 30, 2017 (1) United States $ 228.7 $ — $ 230.6 $ 0.8 $ 10.2 $ 470.3 Europe 361.2 456.1 634.0 427.9 145.9 2,025.1 Asia-Pacific 243.6 — 106.8 271.5 148.8 770.7 Rest of World 13.2 — 67.0 — — 80.2 Total $ 846.7 $ 456.1 $ 1,038.4 $ 700.2 $ 304.9 $ 3,346.3 (1) As the Company has adopted Topic 606 utilizing the modified retrospective approach, amounts for the three and nine months ended September 30, 2017 above are disclosed as recognized under Topic 605.

Investments in Unconsolidated_2

Investments in Unconsolidated Affiliates (Tables)	9 Months Ended
	Sep. 30, 2018
Investments in Unconsolidated Affiliates
Summarized Financial Information of Unconsolidated Affiliates	Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Sales $ 462.1 $ 458.7 $ 1,430.2 $ 1,369.6 Gross profit $ 74.1 $ 90.6 $ 242.3 $ 176.4 Net income $ 62.1 $ 81.1 $ 206.4 $ 141.5

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2018
Inventories
Schedule of Inventories	September 30, December 31, 2018 2017 Finished goods $ 292.7 $ 250.9 Raw materials and semi-finished goods 254.9 226.7 Supplies 38.0 32.8 Total $ 585.6 $ 510.4

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt
Schedule of Debt [Table Text Block]	September 30, 2018 December 31, 2017 Interest Rate as of Maturity Carrying Unamortized (1) Total Debt, Carrying Unamortized (1) Total Debt, Senior Credit Facility 2022 Revolving Facility (2) Various September 2022 $ — $ — $ — $ — $ — $ — 2024 Term Loan B (3) 4.242% September 2024 693.0 (16.9) 676.1 698.3 (18.3) 680.0 2025 Senior Notes 5.375% September 2025 500.0 (8.6) 491.4 500.0 (9.4) 490.6 Accounts Receivable Securitization Facility (4) Various September 2021 — — — — — — Other indebtedness Various Various 1.2 — 1.2 1.4 — 1.4 Total debt $ 1,194.2 $ (25.5) $ 1,168.7 $ 1,199.7 $ (27.7) $ 1,172.0 Less: current portion (7.0) (7.0) Total long-term debt, net of unamortized deferred financing fees $ 1,161.7 $ 1,165.0 (1) This caption does not include deferred financing fees related to the Company’s revolving facilities, which are included within “Deferred charges and other assets” on the condensed consolidated balance sheets. (2) Under the 2022 Revolving Facility, the Company had a capacity of $375.0 million and funds available for borrowing of $360.5 million (net of $14.5 million outstanding letters of credit) as of September 30, 2018. Additionally, the Company is required to pay a quarterly commitment fee in respect of any unused commitments under this facility equal to 0.375% per annum. (3) As of September 30, 2018, $7.0 million of the scheduled future payments related to this facility were classified as current debt on the Company’s condensed consolidated balance sheet. (4) This facility had a borrowing capacity of $150.0 million as of September 30, 2018. Additionally, a s of September 30, 2018, the Company had accounts receivable available to support this facility in excess of its borrowing capacity, based on the pool of eligible accounts receivable. In regard to outstanding borrowings, fixed interest charges are 1.95% plus variable commercial paper rates, while for available, but undrawn commitments, fixed interest charges are 1.00%. As a result of an amendment that was executed during the third quarter of 2018, this facility now has a maturity date of September 2021.

Goodwill (Tables)

Goodwill (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill.
Changes in Carrying Amount of Goodwill, by Segment	Latex Synthetic Performance Americas Binders Rubber Plastics Polystyrene Feedstocks Styrenics Total Balance at December 31, 2017 $ 16.5 $ 11.7 $ 39.6 $ 4.7 $ — $ — $ 72.5 Foreign currency impact (0.4) (0.3) (1.8) (0.1) — — (2.6) Balance at September 30, 2018 $ 16.1 $ 11.4 $ 37.8 $ 4.6 $ — $ — $ 69.9

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments [Abstract]
Notional Amounts of Most Significant Net Foreign Exchange Hedge Positions Outstanding	September 30, Buy / (Sell) 2018 Euro $ (301.1) Chinese Yuan $ (54.1) Swiss Franc $ 51.4 Mexican Peso $ (13.1) Indonesian Rupiah $ (11.5)
Schedule of Effect of Derivative Instruments on Statements of Operations	Location and Amount of Gain (Loss) Recognized in Three Months Ended Three Months Ended September 30, 2018 September 30, 2017 Cost of Interest expense, net Other expense (income), net Cost of Interest expense, net Other expense (income), net Total amounts of income and expense line items presented in the statements of operations in which the effects of derivative instruments are recorded $ 1,068.1 $ 10.1 $ 2.1 $ 948.1 $ 18.4 $ 2.1 The effects of cash flow hedge instruments: Foreign exchange cash flow hedges Amount of loss reclassified from AOCI into income $ (0.6) $ — $ — $ (2.7) $ — $ — Interest rate swaps Amount of gain reclassified from AOCI into income $ — $ 0.1 $ — $ — $ — $ — The effects of net investment hedge instruments: Cross currency swaps (CCS) Amount of gain excluded from effectiveness testing $ — $ 3.8 $ — $ — $ — $ — The effects of derivatives not designated as hedge instruments: Foreign exchange forward contracts Amount of gain (loss) recognized in income $ — $ — $ 8.2 $ — $ — $ (6.5) Location and Amount of Gain (Loss) Recognized in Nine Months Ended Nine Months Ended September 30, 2018 September 30, 2017 Cost of Interest expense, net Other expense (income), net Cost of Interest expense, net Other expense (income), net Total amounts of income and expense line items presented in the statements of operations in which the effects of derivative instruments are recorded $ 3,088.3 $ 35.8 $ 2.9 $ 2,872.3 $ 55.4 $ (0.1) The effects of cash flow hedge instruments: Foreign exchange cash flow hedges Amount of gain (loss) reclassified from AOCI into income $ (6.8) $ — $ — $ 0.8 $ — $ — Interest rate swaps Amount of gain reclassified from AOCI into income $ — $ 0.1 $ — $ — $ — $ — The effects of net investment hedge instruments: Cross currency swaps (CCS) Amount of gain excluded from effectiveness testing $ — $ 7.7 $ — $ — $ — $ — The effects of derivatives not designated as hedge instruments: Foreign exchange forward contracts Amount of gain (loss) recognized in income $ — $ — $ 17.0 $ — $ — $ (17.0)
Schedule of Effect of Hedges on AOCI	Gain (Loss) Recognized in AOCI on Balance Sheet Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Designated as Cash Flow Hedges Foreign exchange cash flow hedges $ 1.2 $ (4.5) $ 11.3 $ (22.2) Interest rate swaps 0.9 0.8 5.5 0.7 Total $ 2.1 $ (3.7) $ 16.8 $ (21.5) Designated as Net Investment Hedges Euro Notes $ — $ (13.9) $ — $ (38.6) Cross currency swaps (CCS) (0.6) (7.1) 9.7 (7.1) Total $ (0.6) $ (21.0) $ 9.7 $ (45.7)
Schedule of Gross and Net Unrealized Gains and Losses and Balance Sheet Classification	September 30, 2018 Foreign Foreign Exchange Exchange Interest Cross Balance Sheet Forward Cash Flow Rate Currency Classification Contracts Hedges Swaps Swaps Total Asset Derivatives: Accounts receivable, net of allowance $ 4.4 $ 0.9 $ 1.6 $ 5.7 $ 12.6 Deferred charges and other assets — — 6.8 — 6.8 Gross derivative asset position 4.4 0.9 8.4 5.7 19.4 Less: Counterparty netting (0.8) (0.2) — — (1.0) Net derivative asset position $ 3.6 $ 0.7 $ 8.4 $ 5.7 $ 18.4 Liability Derivatives: Accounts payable $ (1.4) $ (0.9) $ — $ — $ (2.3) Other noncurrent obligations — — — (16.2) (16.2) Gross derivative liability position (1.4) (0.9) — (16.2) (18.5) Less: Counterparty netting 0.8 0.2 — — 1.0 Net derivative liability position $ (0.6) $ (0.7) $ — $ (16.2) $ (17.5) Total net derivative position $ 3.0 $ — $ 8.4 $ (10.5) $ 0.9 December 31, 2017 Foreign Foreign Exchange Exchange Interest Cross Balance Sheet Forward Cash Flow Rate Currency Classification Contracts Hedges Swaps Swaps Total Asset Derivatives: Accounts receivable, net of allowance $ 0.7 $ — $ — $ 10.8 $ 11.5 Deferred charges and other assets — — 3.0 — 3.0 Gross derivative asset position 0.7 — 3.0 10.8 14.5 Less: Counterparty netting (0.6) — — — (0.6) Net derivative asset position $ 0.1 $ — $ 3.0 $ 10.8 $ 13.9 Liability Derivatives: Accounts payable $ (3.1) $ (11.1) $ (0.1) $ — $ (14.3) Other noncurrent obligations — — — (28.3) (28.3) Gross derivative liability position (3.1) (11.1) (0.1) (28.3) (42.6) Less: Counterparty netting 0.6 — — — 0.6 Net derivative liability position $ (2.5) $ (11.1) $ (0.1) $ (28.3) $ (42.0) Total net derivative position $ (2.4) $ (11.1) $ 2.9 $ (17.5) $ (28.1)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Measurements
Schedule of Assets and Liabilities at Fair Value on Recurring Basis	September 30, 2018 Quoted Prices in Active Markets for Identical Items Significant Other Observable Inputs Significant Unobservable Inputs Assets (Liabilities) at Fair Value (Level 1) (Level 2) (Level 3) Total Foreign exchange forward contracts—Assets $ — $ 3.6 $ — $ 3.6 Foreign exchange forward contracts—(Liabilities) — (0.6) — (0.6) Foreign exchange cash flow hedges—Assets — 0.7 — 0.7 Foreign exchange cash flow hedges—(Liabilities) — (0.7) — (0.7) Interest rate swaps—Assets — 8.4 — 8.4 Cross currency swaps—Assets — 5.7 — 5.7 Cross currency swaps—(Liabilities) — (16.2) — (16.2) Total fair value $ — $ 0.9 $ — $ 0.9 December 31, 2017 Quoted Prices in Active Markets for Identical Items Significant Other Observable Inputs Significant Unobservable Inputs Assets (Liabilities) at Fair Value (Level 1) (Level 2) (Level 3) Total Foreign exchange forward contracts—Assets $ — $ 0.1 $ — $ 0.1 Foreign exchange forward contracts—(Liabilities) — (2.5) — (2.5) Foreign exchange cash flow hedges—(Liabilities) — (11.1) — (11.1) Interest rate swaps—Assets — 3.0 — 3.0 Interest rate swaps—(Liabilities) — (0.1) — (0.1) Cross currency swaps—Assets — 10.8 — 10.8 Cross currency swaps—(Liabilities) — (28.3) — (28.3) Total fair value $ — $ (28.1) $ — $ (28.1)
Estimated Fair Value of Outstanding Debt Not Carried at Fair Value	As of As of September 30, 2018 December 31, 2017 2025 Senior Notes $ 483.3 $ 518.8 2024 Term Loan B 694.3 705.7 Total fair value $ 1,177.6 $ 1,224.5

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2018
Provision for Income Taxes
Schedule of Effective Tax Rate	Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Effective income tax rate 20.5 % 20.0 % 18.0 % 21.1 %

Pension Plans and Other Postr_2

Pension Plans and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2018
Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Schedule of Net Periodic Benefit Costs	Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Defined Benefit Pension Plans Service cost $ 3.0 $ 5.0 $ 9.2 $ 14.3 Interest cost 1.2 1.2 3.7 3.4 Expected return on plan assets (0.5) (0.5) (1.6) (1.3) Amortization of prior service credit (0.3) (0.5) (0.9) (1.5) Amortization of net loss 0.8 1.5 2.7 4.3 Net settlement and curtailment loss (1) — — — 0.1 Net periodic benefit cost $ 4.2 $ 6.7 $ 13.1 $ 19.3 (1) Represents a settlement loss of approximately $0.5 million triggered by benefit payments exceeding the sum of service and interest cost for one of the Company’s pension plans in Switzerland, partially offset by a curtailment gain of approximately $0.4 million related to a reduction in the number of participants in the Company’s pension plan in Japan.
Other Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Schedule of Net Periodic Benefit Costs	Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Other Postretirement Plans Service cost $ — $ — $ 0.1 $ 0.1 Interest cost 0.1 0.1 0.2 0.2 Amortization of prior service cost — — 0.1 0.1 Amortization of net gain — — — — Net periodic benefit cost $ 0.1 $ 0.1 $ 0.4 $ 0.4

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Stock-Based Compensation Expense and Unrecognized Compensation Cost	As of Three Months Ended Nine Months Ended September 30, 2018 September 30, September 30, Unrecognized Weighted 2018 2017 2018 2017 Compensation Cost Average Years RSUs $ 2.3 $ 2.3 $ 6.6 $ 6.3 $ 12.4 2.0 Options 0.5 0.5 3.9 3.7 1.8 1.3 PSUs 0.6 0.3 1.8 0.8 6.6 2.3 Total stock-based compensation expense $ 3.4 $ 3.1 $ 12.3 $ 10.8
Summary of Awards Granted and Weighted Average Grant-Date Fair Value	Nine Months Ended September 30, 2018 Awards Granted Weighted Average Grant Date Fair Value per Award RSUs 131,240 $ 79.18 Options 202,963 22.29 PSUs 70,301 86.78
Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Weighted-average Assumptions	Nine Months Ended September 30, 2018 Expected term (in years) 5.50 Expected volatility 32.00 % Risk-free interest rate 2.71 % Dividend yield 2.00 %
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Weighted-average Assumptions	Nine Months Ended September 30, 2018 Expected term (in years) 3.00 Expected volatility 35.03 % Risk-free interest rate 2.55 % Share Price $ 79.42

Segments (Tables)

Segments (Tables)	9 Months Ended
	Sep. 30, 2018
Segments
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Latex Synthetic Performance Americas Corporate Three Months Ended Binders Rubber Plastics Polystyrene Feedstocks Styrenics Unallocated Total September 30, 2018 Sales to external customers $ 278.0 $ 137.7 $ 400.7 $ 252.3 $ 131.0 $ — $ — $ 1,199.7 Equity in earnings of unconsolidated affiliates — — — — — 34.5 — 34.5 Adjusted EBITDA (1) 24.7 15.5 43.8 5.0 40.3 34.5 Investment in unconsolidated affiliates — — — — — 180.8 — 180.8 Depreciation and amortization 6.2 10.6 6.9 2.9 2.9 — 2.3 31.8 September 30, 2017 Sales to external customers $ 266.3 $ 118.7 $ 362.2 $ 238.4 $ 111.0 $ — $ — $ 1,096.6 Equity in earnings of unconsolidated affiliates — — — — — 43.8 — 43.8 Adjusted EBITDA (1) 32.3 (5.6) 62.4 9.1 45.6 43.8 Investment in unconsolidated affiliates — — — — — 161.9 — 161.9 Depreciation and amortization 6.0 9.0 5.3 3.1 3.6 — 2.2 29.2 Latex Synthetic Performance Americas Corporate Nine Months Ended Binders Rubber Plastics Polystyrene Feedstocks Styrenics Unallocated Total September 30, 2018 Sales to external customers $ 814.2 $ 442.2 $ 1,216.2 $ 777.5 $ 307.7 $ — $ — $ 3,557.8 Equity in earnings of unconsolidated affiliates — — — — — 113.3 — 113.3 Adjusted EBITDA (1) 88.2 71.6 158.2 28.0 114.3 113.3 Investment in unconsolidated affiliates — — — — — 180.8 — 180.8 Depreciation and amortization 18.6 33.1 20.0 8.6 8.9 — 6.8 96.0 September 30, 2017 Sales to external customers $ 846.7 $ 456.1 $ 1,038.4 $ 700.2 $ 304.9 $ — $ — $ 3,346.3 Equity in earnings of unconsolidated affiliates — — 0.8 — — 92.2 — 93.0 Adjusted EBITDA (1) 105.2 68.4 162.9 29.6 86.3 92.2 Investment in unconsolidated affiliates — — — — — 161.9 — 161.9 Depreciation and amortization 17.5 26.0 13.7 7.3 9.2 — 6.4 80.1 (1)
Reconciliation of IBT to Adjusted EBITDA	Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Income before income taxes $ 93.9 $ 41.5 $ 357.8 $ 267.1 Interest expense, net 10.1 18.4 35.8 55.4 Depreciation and amortization 31.8 29.2 96.0 80.1 Corporate Unallocated (2) 20.9 21.8 65.6 70.8 Adjusted EBITDA Addbacks (3) 7.1 76.7 18.4 71.2 Segment Adjusted EBITDA $ 163.8 $ 187.6 $ 573.6 $ 544.6 (2) (3) Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Loss on extinguishment of long-term debt (Note 6) $ — $ 65.3 $ 0.2 $ 65.3 Net loss (gain) on disposition of businesses and assets (Note 4) — 0.2 (0.5) (9.7) Restructuring and other charges (Note 16) 0.9 1.5 2.6 4.8 Acquisition transaction and integration costs (Note 14) 0.1 3.8 0.6 4.9 Asset impairment charges or write-offs (a) — 4.3 — 4.3 Other items (b) 6.1 1.6 15.5 1.6 Total Adjusted EBITDA Addbacks $ 7.1 $ 76.7 $ 18.4 $ 71.2 (a) Asset impairment charges for the three and nine months ended September 30, 2017 primarily relate to the impairment of certain long-lived assets in the Company’s Performance Plastics segment. (b) Other items for the three and nine months ended September 30, 2018 primarily relate to advisory and professional fees incurred in conjunction with the Company’s initiative to transition business services from Dow, including certain administrative services such as accounts payable, logistics, and IT services. Also included within other items for the nine months ended September 30, 2018 are fees incurred in conjunction with the Company’s 2024 Term Loan B repricing which was completed during the second quarter of 2018. Other items for the three and nine months ended September 30, 2017 primarily relate to fees incurred in conjunction with the Company’s debt refinancing which was completed during the third quarter of 2017.

Restructuring (Tables)

Restructuring (Tables)	9 Months Ended
	Sep. 30, 2018
Restructuring
Detail of Restructuring Charges	Three Months Ended Nine Months Ended Cumulative September 30, September 30, Life-to-date 2018 2017 2018 2017 Charges Segment Terneuzen Compounding Restructuring (1) Asset impairment/accelerated depreciation $ 0.3 $ 0.6 $ 0.8 $ 1.7 $ 2.9 Employee termination benefits 0.1 0.2 0.5 0.3 0.9 Contract terminations — — — 0.6 0.6 Decommissioning and other 0.3 0.2 0.5 0.2 1.3 Terneuzen Subtotal $ 0.7 $ 1.0 $ 1.8 $ 2.8 $ 5.7 Performance Plastics Livorno Plant Restructuring (2) Asset impairment/accelerated depreciation $ — $ — $ 0.4 $ — $ 14.7 Employee termination benefits — 0.2 — 0.6 5.4 Contract terminations — — — — 0.3 Decommissioning and other 0.2 0.6 0.6 1.7 3.6 Livorno Subtotal $ 0.2 $ 0.8 $ 1.0 $ 2.3 $ 24.0 Latex Binders Other Restructurings 0.3 0.3 0.7 1.5 Various Total Restructuring Charges $ 1.2 $ 2.1 $ 3.5 $ 6.6 (1) In March 2017, the Company announced plans to upgrade its production capability for compounded resins with the construction of a new state-of-the art compounding facility to replace its existing compounding facility in Terneuzen, The Netherlands. The new facility is expected to be operational by the end of 2018 with ongoing customer qualifications into early 2019. Further, substantive production at the existing facility is expected to cease during the first half of 2019, followed by decommissioning activities in 2019 and 2020. The Company expects to incur incremental accelerated depreciation charges of approximately $0.3 million through the end of 2018, as well as decommissioning and other charges of approximately $0.6 million throughout 2019, the majority of which are expected to be paid throughout 2019. (2) In August 2016, the Company announced its plan to cease manufacturing activities at its latex binders manufacturing facility in Livorno, Italy. Production at the facility ceased in October 2016 and decommissioning activities began in the fourth quarter of 2016. In June 2018, the Company entered into a preliminary agreement to sell the land where the former facility is located, subject to certain activities being completed prior to closing. In conjunction with the execution of this agreement, the Company received approximately $1.3 million of the purchase price as a prepayment, which has been deferred and recorded within “Accrued expenses and other current liabilities” on the condensed consolidated balance sheet as of September 30, 2018. The Company expects to record an immaterial gain on sale when the transaction is completed. Furthermore, as this sale is considered probable within one year of the balance sheet date, the Company recorded the $12.2 million of land as held-for-sale within “Other current assets”, as well as a deferred tax liability associated with that land of $2.9 million as held-for-sale within “Accrued expenses and other current liabilities”, on the condensed consolidated balance sheet as of September 30, 2018. The Company will continue to incur additional decommissioning costs associated with this plant shutdown through the closing date of the sale, the cost of which will be expensed as incurred.
Rollforward of Liability Balances	Balance at Balance at December 31, 2017 Expenses Deductions (1) September 30, 2018 Employee termination benefits $ 1.4 $ 0.5 $ (0.9) $ 1.0 Contract terminations 0.6 — — 0.6 Decommissioning and other — 1.8 (1.8) — Total $ 2.0 $ 2.3 $ (2.7) $ 1.6 (1) Primarily includes payments made against the existing accrual, as well as immaterial impacts of foreign currency remeasurement. .

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2018
Shareholders' Equity.
Components of AOCI, Net of Income Taxes	Cumulative Pension & Other Translation Postretirement Benefit Cash Flow Three Months Ended September 30, 2018 and 2017 Adjustments Plans, Net Hedges, Net Total Balance as of June 30, 2018 $ (112.7) $ (43.8) $ 8.6 $ (147.9) Other comprehensive income (loss) (4.6) — 1.6 (3.0) Amounts reclassified from AOCI to net income (1) — 0.6 0.5 1.1 Balance as of September 30, 2018 $ (117.3) $ (43.2) $ 10.7 $ (149.8) Balance as of June 30, 2017 $ (95.8) $ (61.3) $ (5.5) $ (162.6) Other comprehensive loss (1.6) — (6.4) (8.0) Amounts reclassified from AOCI to net income (1) — 0.8 2.7 3.5 Balance as of September 30, 2017 $ (97.4) $ (60.5) $ (9.2) $ (167.1) Cumulative Pension & Other Translation Postretirement Benefit Cash Flow Nine Months Ended September 30, 2018 and 2017 Adjustments Plans, Net Hedges, Net Total Balance at December 31, 2017 $ (94.5) $ (45.0) $ (6.1) $ (145.6) Other comprehensive income (loss) (22.8) — 10.1 (12.7) Amounts reclassified from AOCI to net income (1) — 1.8 6.7 8.5 Balance at September 30, 2018 $ (117.3) $ (43.2) $ 10.7 $ (149.8) Balance as of December 31, 2016 $ (119.0) $ (63.5) $ 12.3 $ (170.2) Other comprehensive income (loss) 21.6 — (20.7) 0.9 Amounts reclassified from AOCI to net income (1) — 3.0 (0.8) 2.2 Balance as of September 30, 2017 $ (97.4) $ (60.5) $ (9.2) $ (167.1)
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	(1) The following is a summary of amounts reclassified from AOCI to net income for the three and nine months ended September 30, 2018 and 2017: Amount Reclassified from AOCI Amount Reclassified from AOCI AOCI Components Three Months Ended September 30, Nine Months Ended September 30, Statements of Operations 2018 2017 2018 2017 Classification Cash flow hedging items Foreign exchange cash flow hedges $ 0.6 $ 2.7 $ 6.8 $ (0.8) Cost of sales Interest rate swaps (0.1) — (0.1) — Interest expense, net Total before tax 0.5 2.7 6.7 (0.8) Tax effect — — — — Provision for income taxes Total, net of tax $ 0.5 $ 2.7 $ 6.7 $ (0.8) Amortization of pension and other postretirement benefit plan items Prior service credit $ (0.2) $ (0.5) $ (0.7) $ (1.4) (a) Net actuarial loss 1.0 1.7 3.2 4.9 (a) Net settlement and curtailment loss — — — 0.6 (a) Total before tax 0.8 1.2 2.5 4.1 Tax effect (0.2) (0.4) (0.7) (1.1) Provision for income taxes Total, net of tax $ 0.6 $ 0.8 $ 1.8 $ 3.0 (a) These AOCI components are included in the computation of net periodic benefit costs (see Note 12). .

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share
Schedule of Earnings per Share Basic and Diluted	Three Months Ended Nine Months Ended September 30, September 30, (in millions, except per share data) 2018 2017 2018 2017 Earnings: Net income $ 74.7 $ 33.2 $ 293.3 $ 210.7 Shares: Weighted average ordinary shares outstanding 42.6 43.7 43.0 43.9 Dilutive effect of RSUs, option awards, and PSUs (1) 0.7 1.1 0.9 1.1 Diluted weighted average ordinary shares outstanding 43.3 44.8 43.9 45.0 Income per share: Income per share—basic $ 1.75 $ 0.76 $ 6.82 $ 4.80 Income per share—diluted $ 1.72 $ 0.74 $ 6.68 $ 4.68 (1)

Recent Accounting Guidance - Re

Recent Accounting Guidance - Revenue Recognition (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 770.9		$ 527.9
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings		$ 0

Recent Accounting Guidance - Ot

Recent Accounting Guidance - Other (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales	$ 1,068.1	$ 948.1	$ 3,088.3	$ 2,872.3
Selling, general and administrative expenses	$ 60	65	$ 186.1	179.3
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		(1.4)		(3.8)
Selling, general and administrative expenses		$ (0.7)		$ (2.2)

Net Sales (Details)

Net Sales (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue, Practical Expedient, Incremental Cost of Obtaining Contract [true false]			true
Revenue, Practical Expedient, Financing Component [true false]			true
Revenue, Remaining Performance Obligation, Optional Exemption, Performance Obligation [true false]			true
Revenue, Practical Expedient, Initial Application and Transition, Completed Contract, Use of Transaction Price at Contract Completion Date [true false]			true
Net sales	$ 1,199.7	$ 1,096.6	$ 3,557.8	$ 3,346.3
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		1,096.6		3,346.3
Minimum
Disaggregation of Revenue [Line Items]
Product sales payment terms			10 days
Maximum
Disaggregation of Revenue [Line Items]
Product sales payment terms			90 days
Weighted Average [Member]
Disaggregation of Revenue [Line Items]
Product sales payment terms			53 days
Latex Binders Segment
Disaggregation of Revenue [Line Items]
Net sales	278		$ 814.2
Latex Binders Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		266.3		846.7
Synthetic Rubber Segment
Disaggregation of Revenue [Line Items]
Net sales	137.7		442.2
Synthetic Rubber Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		118.7		456.1
Performance Plastics Segment [Member]
Disaggregation of Revenue [Line Items]
Net sales	400.7		1,216.2
Performance Plastics Segment [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		362.2		1,038.4
Polystyrene [Member]
Disaggregation of Revenue [Line Items]
Net sales	252.3		777.5
Polystyrene [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		238.4		700.2
Feedstocks [Member]
Disaggregation of Revenue [Line Items]
Net sales	131		307.7
Feedstocks [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		111		304.9
United States [Member]
Disaggregation of Revenue [Line Items]
Net sales	167.3		479.8
United States [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		154.1		470.3
United States [Member] | Latex Binders Segment
Disaggregation of Revenue [Line Items]
Net sales	77.3		216.3
United States [Member] | Latex Binders Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		73.7		228.7
United States [Member] | Performance Plastics Segment [Member]
Disaggregation of Revenue [Line Items]
Net sales	87		253.7
United States [Member] | Performance Plastics Segment [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		76.8		230.6
United States [Member] | Polystyrene [Member]
Disaggregation of Revenue [Line Items]
Net sales			0.2
United States [Member] | Polystyrene [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		0.1		0.8
United States [Member] | Feedstocks [Member]
Disaggregation of Revenue [Line Items]
Net sales	3		9.6
United States [Member] | Feedstocks [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		3.5		10.2
Europe [Member]
Disaggregation of Revenue [Line Items]
Net sales	690.9		2,148.1
Europe [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		662		2,025.1
Europe [Member] | Latex Binders Segment
Disaggregation of Revenue [Line Items]
Net sales	117		349.6
Europe [Member] | Latex Binders Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		113		361.2
Europe [Member] | Synthetic Rubber Segment
Disaggregation of Revenue [Line Items]
Net sales	137.7		442.2
Europe [Member] | Synthetic Rubber Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		118.7		456.1
Europe [Member] | Performance Plastics Segment [Member]
Disaggregation of Revenue [Line Items]
Net sales	226.7		720.9
Europe [Member] | Performance Plastics Segment [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		223.6		634
Europe [Member] | Polystyrene [Member]
Disaggregation of Revenue [Line Items]
Net sales	148.3		460.9
Europe [Member] | Polystyrene [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		144.9		427.9
Europe [Member] | Feedstocks [Member]
Disaggregation of Revenue [Line Items]
Net sales	61.2		174.5
Europe [Member] | Feedstocks [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		61.8		145.9
Asia-Pacific [Member]
Disaggregation of Revenue [Line Items]
Net sales	313.5		847.9
Asia-Pacific [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		253.5		770.7
Asia-Pacific [Member] | Latex Binders Segment
Disaggregation of Revenue [Line Items]
Net sales	80		236.9
Asia-Pacific [Member] | Latex Binders Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		75.3		243.6
Asia-Pacific [Member] | Performance Plastics Segment [Member]
Disaggregation of Revenue [Line Items]
Net sales	62.7		171
Asia-Pacific [Member] | Performance Plastics Segment [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		39.1		106.8
Asia-Pacific [Member] | Polystyrene [Member]
Disaggregation of Revenue [Line Items]
Net sales	104		316.4
Asia-Pacific [Member] | Polystyrene [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		93.4		271.5
Asia-Pacific [Member] | Feedstocks [Member]
Disaggregation of Revenue [Line Items]
Net sales	66.8		123.6
Asia-Pacific [Member] | Feedstocks [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		45.7		148.8
Rest of World [Member]
Disaggregation of Revenue [Line Items]
Net sales	28		82
Rest of World [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		27		80.2
Rest of World [Member] | Latex Binders Segment
Disaggregation of Revenue [Line Items]
Net sales	3.7		11.4
Rest of World [Member] | Latex Binders Segment | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		4.3		13.2
Rest of World [Member] | Performance Plastics Segment [Member]
Disaggregation of Revenue [Line Items]
Net sales	$ 24.3		$ 70.6
Rest of World [Member] | Performance Plastics Segment [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Net sales		$ 22.7		$ 67

Investments in Unconsolidated_3

Investments in Unconsolidated Affiliates - Summarized Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Summarized Financial Information, Net Income
Sales	$ 462.1	$ 458.7	$ 1,430.2	$ 1,369.6
Gross profit	74.1	90.6	242.3	176.4
Net income	$ 62.1	$ 81.1	$ 206.4	$ 141.5

Investments in Unconsolidated_4

Investments in Unconsolidated Affiliates (Details) $ in Millions	Jan. 31, 2017USD ($)	Sep. 30, 2018USD ($)item	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)item	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Investments in Unconsolidated Affiliates
Number of joint ventures | item		1		1
Equity in earnings of unconsolidated affiliates		$ 34.5	$ 43.8	$ 113.3	$ 93
Investments in unconsolidated affiliates		180.8	161.9	180.8	161.9	$ 152.5
Americas Styrenics
Investments in Unconsolidated Affiliates
Investments in unconsolidated affiliates		180.8		180.8		152.5
Investment in unconsolidated affiliates-difference between carrying amount and underlying equity		$ 36.6		$ 36.6		$ 46.4
Percentage of ownership underlying net assets		50.00%		50.00%		50.00%
Amortized weighted average remaining useful life				P2Y1M6D
Dividends received from operating activities		$ 17.5	35	$ 85	80
Sumika Styron Polycarbonate
Investments in Unconsolidated Affiliates
Investments in unconsolidated affiliates						$ 0
Percentage of ownership underlying net assets	50.00%
Sales proceeds	$ 42.1
Gain on sale					9.3
Dividends received from operating and investing activities			$ 0		$ 9.8

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Inventories
Finished goods	$ 292.7	$ 250.9
Raw materials and semi-finished goods	254.9	226.7
Supplies	38	32.8
Total	$ 585.6	$ 510.4

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) € in Millions, $ in Millions	May 22, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	May 21, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Aug. 31, 2017EUR (€)	Aug. 29, 2017USD ($)
Debt Instruments
Carrying amount		$ 1,194.2			$ 1,194.2		$ 1,199.7
Unamortized deferred financing fees		(25.5)			(25.5)		(27.7)
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent		1,168.7			1,168.7		1,172
Less: current portion		(7)			(7)		(7)
Total long-term debt, net of unamortized deferred financing fees		1,161.7			1,161.7		1,165
Interest and Debt Expense [Abstract]
Call premium						$ 53
Loss on extinguishment of debt			$ 65.3		0.2	65.3
2022 Revolving Facility
Debt Instruments
Funds available for borrowings		360.5			360.5
Letters of credit, amount outstanding		14.5			$ 14.5
Commitment fee (as a percent)					0.375%
Maximum borrowing capacity		$ 375	375		$ 375	375
2024 Term Loan B
Debt Instruments
Interest rate		4.242%			4.242%
Carrying amount		$ 693	$ 700		$ 693	$ 700	698.3
Unamortized deferred financing fees		(16.9)		$ (16.4)	(16.9)		(18.3)
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent		676.1			676.1		680
Less: current portion		$ (7)			(7)
Interest and Debt Expense [Abstract]
Write-off of unamortized deferred financing fees					0.2
Debt repricing costs incurred	$ 1.1
Debt issuance fees expensed					$ 0.5
Capitalization of issuance costs	$ 0.6
Deferred financing costs, amortization period	7 years
2024 Term Loan B | LIBOR [Member]
Debt Instruments
Debt instrument, margin rate	2.00%	2.00%		2.50%		2.50%
Variable rate floor (as a percent)		0.00%				0.00%
2025 Senior Notes
Debt Instruments
Interest rate		5.375%	5.375%		5.375%	5.375%			5.375%
Carrying amount		$ 500	$ 500		$ 500	$ 500	500
Unamortized deferred financing fees		(8.6)			(8.6)		(9.4)
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent		491.4			491.4		490.6		$ 500
Accounts Receivable Securitization Facility [Member]
Debt Instruments
Carrying amount		0			0		0
Unamortized deferred financing fees		0			0		0
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent		0			$ 0		0
Commitment fee (as a percent)					1.00%
Maximum borrowing capacity		$ 150			$ 150
Accounts Receivable Securitization Facility [Member] | Base Rate [Member]
Debt Instruments
Interest rate		1.95%			1.95%
Other Indebtedness [Member]
Debt Instruments
Carrying amount		$ 1.2			$ 1.2		1.4
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent		$ 1.2			$ 1.2		$ 1.4
2022 Senior Notes
Interest and Debt Expense [Abstract]
Call premium						53
Loss on extinguishment of debt			$ 65.3			$ 65.3
Euro Notes
Debt Instruments
Total Debt, Less Unamortized Deferred Financing Fees, Current and Noncurrent | €								€ 375

Goodwill (Details)

Goodwill (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 72.5
Foreign currency impact	(2.6)
Ending Balance	69.9
Latex Binders Segment
Goodwill [Roll Forward]
Beginning Balance	16.5
Foreign currency impact	(0.4)
Ending Balance	16.1
Synthetic Rubber Segment
Goodwill [Roll Forward]
Beginning Balance	11.7
Foreign currency impact	(0.3)
Ending Balance	11.4
Performance Plastics Segment [Member]
Goodwill [Roll Forward]
Beginning Balance	39.6
Foreign currency impact	(1.8)
Ending Balance	37.8
Polystyrene [Member]
Goodwill [Roll Forward]
Beginning Balance	4.7
Foreign currency impact	(0.1)
Ending Balance	$ 4.6

Derivative Instruments (Details

Derivative Instruments (Details) € in Millions, $ in Millions

May 22, 2018

Sep. 01, 2017USD ($)

Sep. 30, 2018USD ($)

May 21, 2018

Sep. 30, 2018USD ($)item

Sep. 30, 2017

Apr. 01, 2018USD ($)

Mar. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Sep. 01, 2017EUR (€)

Aug. 31, 2017EUR (€)

Aug. 29, 2017USD ($)

Derivative Instruments

Total debt

$ 1,168.7

$ 1,168.7

$ 1,172

Foreign Exchange Forward Contracts

Derivative Instruments

Derivative term

2 months

Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

487.1

$ 487.1

Foreign Exchange Forward Contracts | Designated as Hedging Instrument

Derivative Instruments

Derivative contracts, notional amount

124.8

$ 124.8

Derivative term

15 months

Number of subsidiaries participating | item

1

Cross Currency Swap | Net Investment Hedges

Derivative Instruments

Derivative contracts, notional amount | €

€ 420

Derivative term

5 years

Cross currency swap weighted average interest rate (as a percent)

3.45%

Amount hedged

$ 500

Cumulative translation adjustment, net of tax

$ 38

Initial excluded component value

$ 23.6

Debt Instrument Hedge | Net Investment Hedges

Derivative Instruments

Total debt | €

€ 280

Cumulative translation adjustment, net of tax

24.1

Interest Rate Swap

Derivative Instruments

Derivative contracts, notional amount

$ 200

$ 200

Derivative term

5 years

Fixed interest rate per agreement (as a percent)

1.81%

1.81%

LIBOR rate at end of period (as a percent)

2.24%

2.24%

Euro Notes

Derivative Instruments

Total debt | €

€ 375

2025 Senior Notes

Derivative Instruments

Total debt

$ 491.4

$ 491.4

490.6

$ 500

Interest rate

5.375%

5.375%

5.375%

5.375%

2024 Term Loan B

Derivative Instruments

Total debt

$ 676.1

$ 676.1

$ 680

Interest rate

4.242%

4.242%

2024 Term Loan B | LIBOR [Member]

Derivative Instruments

Debt instrument, margin rate

2.00%

2.00%

2.50%

2.50%

Variable rate floor (as a percent)

0.00%

0.00%

Euro [Member] | Foreign Exchange Forward Contracts | Sell | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

$ 301.1

$ 301.1

Chinese Yuan [Member] | Foreign Exchange Forward Contracts | Sell | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

54.1

54.1

Swiss Franc [Member] | Foreign Exchange Forward Contracts | Buy | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

51.4

51.4

Mexico, Pesos | Foreign Exchange Forward Contracts | Sell | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

13.1

13.1

Indonesian Rupiah [Member] | Foreign Exchange Forward Contracts | Sell | Not Designated as Hedging Instruments - Economic

Derivative Instruments

Derivative contracts, notional amount

$ 11.5

$ 11.5

Derivative Instruments - Income

Derivative Instruments - Income Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Cost of sales	$ 1,068.1	$ 948.1	$ 3,088.3	$ 2,872.3
Interest expense, net	(10.1)	(18.4)	(35.8)	(55.4)
Other expense (income), net	(2.1)	(2.1)	(2.9)	0.1
Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic | Other Expense (Income), Net
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amount of gain recognized in income, not designated	8.2	(6.5)	17	(17)
Foreign Exchange Forward Contracts | Designated as Hedging Instrument | Cost of Sales
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amount of gain (loss) reclassified from AOCI into income, foreign exchange cash flow hedges	(0.6)	$ (2.7)	(6.8)	$ 0.8
Cross Currency Swap | Interest Expense, Net
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amount of gain excluded from effectiveness testing	3.8		7.7
Interest Rate Swap | Interest Expense, Net
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Amount of gain (loss) reclassified from AOCI into income, interest rate cash flow hedges	$ 0.1		$ 0.1

Derivative Instruments - Effect

Derivative Instruments - Effect on AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments
Gain (Loss) Recognized in AOCI, Cash flow hedges	$ 2.1	$ (3.7)	$ 16.8	$ (21.5)
Gain (Loss) Recognized in AOCI, Net investment hedges	(0.6)	(21)	9.7	(45.7)
Foreign Exchange Forward Contracts
Derivative Instruments
Gain (Loss) Recognized in AOCI, Cash flow hedges	1.2	(4.5)	11.3	(22.2)
Cross Currency Swap
Derivative Instruments
Gain (Loss) Recognized in AOCI, Net investment hedges	(0.6)	(7.1)	9.7	(7.1)
Debt Instrument Hedge
Derivative Instruments
Gain (Loss) Recognized in AOCI, Net investment hedges		(13.9)		(38.6)
Interest Rate Swap
Derivative Instruments
Gain (Loss) Recognized in AOCI, Cash flow hedges	$ 0.9	$ 0.8	$ 5.5	$ 0.7

Derivative Instruments - Gains

Derivative Instruments - Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Foreign exchange transaction gains (losses)	$ (6.9)	$ 8.2	$ (12.6)	$ 16.1
Maximum
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Reclassification expected during next 12 months			(1.6)
Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Gain (loss) from settlements and changes in fair value	$ 8.2	$ (6.5)	$ 17	$ (17)

Derivative Instruments - Financ

Derivative Instruments - Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	$ 19.4	$ 14.5
Counterparty netting, derivative assets	(1)	(0.6)
Net derivative asset position	18.4	13.9
Gross derivative liability position	18.5	42.6
Counterparty netting, derivative liabilities	(1)	(0.6)
Net derivative liability position	17.5	42
Total net derivative position	0.9	(28.1)
Accounts Receivable
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	12.6	11.5
Deferred Charges and Other Assets
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	6.8	3
Accounts Payable
Derivatives, Financial Assets and Liabilities
Gross derivative liability position	2.3	14.3
Other Noncurrent Obligations
Derivatives, Financial Assets and Liabilities
Gross derivative liability position	16.2	28.3
Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	4.4	0.7
Counterparty netting, derivative assets	(0.8)	(0.6)
Net derivative asset position	3.6	0.1
Gross derivative liability position	1.4	3.1
Counterparty netting, derivative liabilities	(0.8)	(0.6)
Net derivative liability position	0.6	2.5
Total net derivative position	3	(2.4)
Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic | Accounts Receivable
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	4.4	0.7
Foreign Exchange Forward Contracts | Not Designated as Hedging Instruments - Economic | Accounts Payable
Derivatives, Financial Assets and Liabilities
Gross derivative liability position	1.4	3.1
Foreign Exchange Forward Contracts | Designated as Hedging Instrument
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	0.9
Counterparty netting, derivative assets	(0.2)
Net derivative asset position	0.7
Gross derivative liability position	0.9	11.1
Counterparty netting, derivative liabilities	(0.2)
Net derivative liability position	0.7	11.1
Total net derivative position		(11.1)
Foreign Exchange Forward Contracts | Designated as Hedging Instrument | Accounts Receivable
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	0.9
Foreign Exchange Forward Contracts | Designated as Hedging Instrument | Accounts Payable
Derivatives, Financial Assets and Liabilities
Gross derivative liability position	0.9	11.1
Interest Rate Swap
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	8.4	3
Net derivative asset position	8.4	3
Gross derivative liability position		0.1
Net derivative liability position		0.1
Total net derivative position	8.4	2.9
Interest Rate Swap | Accounts Receivable
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	1.6
Interest Rate Swap | Deferred Charges and Other Assets
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	6.8	3
Interest Rate Swap | Accounts Payable
Derivatives, Financial Assets and Liabilities
Gross derivative liability position		0.1
Cross Currency Swap
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	5.7	10.8
Net derivative asset position	5.7	10.8
Gross derivative liability position	16.2	28.3
Net derivative liability position	16.2	28.3
Total net derivative position	(10.5)	(17.5)
Cross Currency Swap | Accounts Receivable
Derivatives, Financial Assets and Liabilities
Gross derivative asset position	5.7	10.8
Cross Currency Swap | Other Noncurrent Obligations
Derivatives, Financial Assets and Liabilities
Gross derivative liability position	$ 16.2	$ 28.3

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value, Recurring (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value Measurements
Total net derivative position	$ 0.9	$ (28.1)
Interest Rate Swap
Fair Value Measurements
Total net derivative position	8.4	2.9
Cross Currency Swap
Fair Value Measurements
Total net derivative position	(10.5)	(17.5)
Designated as Hedging Instrument | Foreign Exchange Forward Contracts
Fair Value Measurements
Total net derivative position		(11.1)
Not Designated as Hedging Instruments - Economic | Foreign Exchange Forward Contracts
Fair Value Measurements
Total net derivative position	3	(2.4)
Recurring
Fair Value Measurements
Total net derivative position	0.9	(28.1)
Recurring | Interest Rate Swap
Fair Value Measurements
Assets at fair value	8.4	3
Liabilities at fair value		(0.1)
Recurring | Cross Currency Swap
Fair Value Measurements
Assets at fair value	5.7	10.8
Liabilities at fair value	(16.2)	(28.3)
Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Measurements
Total net derivative position	0.9	(28.1)
Recurring | Significant Other Observable Inputs (Level 2) | Interest Rate Swap
Fair Value Measurements
Assets at fair value	8.4	3
Liabilities at fair value		(0.1)
Recurring | Significant Other Observable Inputs (Level 2) | Cross Currency Swap
Fair Value Measurements
Assets at fair value	5.7	10.8
Liabilities at fair value	(16.2)	(28.3)
Recurring | Designated as Hedging Instrument | Foreign Exchange Forward Contracts
Fair Value Measurements
Assets at fair value	0.7
Liabilities at fair value	(0.7)	(11.1)
Recurring | Designated as Hedging Instrument | Significant Other Observable Inputs (Level 2) | Foreign Exchange Forward Contracts
Fair Value Measurements
Assets at fair value	0.7
Liabilities at fair value	(0.7)	(11.1)
Recurring | Not Designated as Hedging Instruments - Economic | Foreign Exchange Forward Contracts
Fair Value Measurements
Assets at fair value	3.6	0.1
Liabilities at fair value	(0.6)	(2.5)
Recurring | Not Designated as Hedging Instruments - Economic | Significant Other Observable Inputs (Level 2) | Foreign Exchange Forward Contracts
Fair Value Measurements
Assets at fair value	3.6	0.1
Liabilities at fair value	$ (0.6)	$ (2.5)

Fair Value Measurements - Items

Fair Value Measurements - Items not at Fair Value (Details) - Significant Other Observable Inputs (Level 2) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value of Debt Instruments
Total fair value of long term debt	$ 1,177.6	$ 1,224.5
2025 Senior Notes
Fair Value of Debt Instruments
Total fair value of long term debt	483.3	518.8
2024 Term Loan B
Fair Value of Debt Instruments
Total fair value of long term debt	$ 694.3	$ 705.7

Provision for Income Taxes (Det

Provision for Income Taxes (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017
Provision for Income Taxes
Effective tax rate	20.50%	20.00%	18.00%	21.10%
Provision for income taxes	$ 19.2	$ 8.3	$ 64.5	$ 56.4
U.S. federal corporate income tax rate			21.00%		35.00%
Call premium fees, portion with no tax benefit		$ 10.9		10.9
Sumika Styron Polycarbonate
Provision for Income Taxes
Gain on sale				$ 9.3
Percentage ownership interest sold during the period				50

Commitments and Contingencies (

Commitments and Contingencies (Details)	Sep. 30, 2018USD ($)item	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure
Accrued obligations for environmental remediation and restoration costs | $	$ 0	$ 0
Environmental claims asserted | item	0

Commitments and Contingencies -

Commitments and Contingencies - Purchase Commitments (Details)	9 Months Ended
	Sep. 30, 2018
Maximum
Loss Contingencies [Line Items]
Purchase commitment period	4 years
Minimum
Loss Contingencies [Line Items]
Purchase commitment period	1 year

Pension Plans and Other Postr_3

Pension Plans and Other Postretirement Benefits - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Pension Plans
Net periodic benefit cost
Service cost	$ 3	$ 5	$ 9.2	$ 14.3
Interest cost	1.2	1.2	3.7	3.4
Expected return on plan assets	(0.5)	(0.5)	(1.6)	(1.3)
Amortization of prior service cost (credit)	(0.3)	(0.5)	(0.9)	(1.5)
Amortization of net (gain) loss	0.8	1.5	2.7	4.3
Settlement and curtailment gain				0.1
Net periodic benefit cost	$ 4.2	$ 6.7	13.1	$ 19.3
Settlement and curtailment gain			0.5
Defined benefit curtailment gain			$ 0.4
Interest cost, Statements of Operations location	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense
Expected return, Statements of Operations location	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense
Amortization of prior service credit, Statements of Operations location	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense
Amortization of gain (loss), Statements of Operations location	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense
Net settlement and curtailment loss, Statements of Operations location	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense
Amounts recognized in other comprehensive income (loss)
Net periodic benefit cost	$ 4.2	$ 6.7	$ 13.1	$ 19.3
Other Postretirement Plans
Net periodic benefit cost
Service cost			0.1	0.1
Interest cost	0.1	0.1	0.2	0.2
Amortization of prior service cost (credit)			0.1	0.1
Net periodic benefit cost	0.1	0.1	0.4	0.4
Amounts recognized in other comprehensive income (loss)
Net periodic benefit cost	$ 0.1	$ 0.1	$ 0.4	$ 0.4

Pension Plans and Other Postr_4

Pension Plans and Other Postretirement Benefits - Net Amounts Recognized (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Net amounts recognized in the balance sheets at December 31
Noncurrent liabilities	$ (190.2)	$ (190.2)	$ (188.7)
Cash contributions and benefit payments to unfunded plans	1.3	4.4
Expected contributions, remainder of current year	$ 1.9	$ 1.9

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3.4	$ 3.1	$ 12.3	$ 10.8
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2.3	2.3	6.6	6.3
Unrecognized compensation cost	12.4		$ 12.4
Weighted-average period of recognition			2 years
Option Awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	0.5	0.5	$ 3.9	3.7
Unrecognized compensation cost, options	1.8		$ 1.8
Weighted-average period of recognition			1 year 3 months 18 days
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	0.6	$ 0.3	$ 1.8	$ 0.8
Unrecognized compensation cost	$ 6.6		$ 6.6
Weighted-average period of recognition			2 years 3 months 18 days

Stock-Based Compensation - RSUs

Stock-Based Compensation - RSUs (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Other-than-Options, Shares Activity
Granted, Shares | shares	131,240
Other-than-Options, FV Activity
Granted, Weighted-Average Grant Date Fair Value per Share | $ / shares	$ 79.18

Stock-Based Compensation - Opti

Stock-Based Compensation - Options and PSUs (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Options, Additional Disclosures
Proceeds from exercise of option awards	$ 2.6	$ 8.3
Option Awards
Options Outstanding Roll Forward
Granted, Options	202,963
Options, Additional Disclosures
Unrecognized compensation cost, options	$ 1.8
Fair Value Assumptions
Expected term (in years)	5 years 6 months
Expected volatility	32.00%
Risk-free interest rate	2.71%
Dividend yield	2.00%
Options granted, Weighted average grant date fair value	$ 22.29
Performance Share Units
Fair Value Assumptions
Expected term (in years)	3 years
Expected volatility	35.03%
Risk-free interest rate	2.55%
Share Price	$ 79.42
Other-than-Options, Shares Activity
Granted, Shares	70,301
Other-than-Options, FV Activity
Granted, Weighted-Average Grant Date Fair Value per Share	$ 86.78

Acquisitions and Divestitures -

Acquisitions and Divestitures - Acquisition (Details) - USD ($) $ in Millions	Jul. 10, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Purchase price, net of cash acquired						$ 79.7
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		$ 69.9	$ 72.5		$ 69.9
API Applicazioni Plastiche Industriali S.p.A. [Member]
Business Acquisition [Line Items]
Equity interest acquired	100.00%
Gross purchase price	$ 90.6
Cash acquired	8.4
Purchase price, net of cash acquired	$ 82.3		$ 2.6			79.7
Changes to purchase price allocation					0
Transaction costs		$ 0.1		$ 2.4	$ 0.6	$ 3.5

Segments - Reconciliation of Se

Segments - Reconciliation of Segment Reporting to Consolidated (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)division	Jan. 31, 2017
Segment Reporting Information [Line Items]
Number of divisions | division					2
Number of reportable segments | segment			6
Number of segments unchanged from former model | segment			4
Sales to external customers	$ 1,199.7	$ 1,096.6	$ 3,557.8	$ 3,346.3
Equity in earnings of unconsolidated affiliates	34.5	43.8	113.3	93
Adjusted EBITDA	163.8	187.6	573.6	544.6
Investment in unconsolidated affiliates	180.8	161.9	180.8	161.9	$ 152.5
Depreciation and amortization	$ 31.8	29.2	$ 96	80.1
Americas Styrenics
Segment Reporting Information [Line Items]
Percentage of ownership underlying net assets	50.00%		50.00%		50.00%
Investment in unconsolidated affiliates	$ 180.8		$ 180.8		$ 152.5
Sumika Styron Polycarbonate
Segment Reporting Information [Line Items]
Percentage of ownership underlying net assets						50.00%
Investment in unconsolidated affiliates					$ 0
Corporate Unallocated [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2.3	2.2	6.8	6.4
Latex Binders Segment
Segment Reporting Information [Line Items]
Sales to external customers	278		814.2
Latex Binders Segment | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to external customers	278	266.3	814.2	846.7
Adjusted EBITDA	24.7	32.3	88.2	105.2
Depreciation and amortization	6.2	6	18.6	17.5
Synthetic Rubber Segment
Segment Reporting Information [Line Items]
Sales to external customers	137.7		442.2
Synthetic Rubber Segment | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to external customers	137.7	118.7	442.2	456.1
Adjusted EBITDA	15.5	(5.6)	71.6	68.4
Depreciation and amortization	10.6	9	33.1	26
Performance Plastics Segment [Member]
Segment Reporting Information [Line Items]
Sales to external customers	400.7		1,216.2
Performance Plastics Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to external customers	400.7	362.2	1,216.2	1,038.4
Equity in earnings of unconsolidated affiliates				0.8
Adjusted EBITDA	43.8	62.4	158.2	162.9
Depreciation and amortization	6.9	5.3	20	13.7
Polystyrene [Member]
Segment Reporting Information [Line Items]
Sales to external customers	252.3		777.5
Polystyrene [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to external customers	252.3	238.4	777.5	700.2
Adjusted EBITDA	5	9.1	28	29.6
Depreciation and amortization	2.9	3.1	8.6	7.3
Basic Plastics Segment [Member] | Sumika Styron Polycarbonate
Segment Reporting Information [Line Items]
Percentage of ownership underlying net assets						50.00%
Feedstocks [Member]
Segment Reporting Information [Line Items]
Sales to external customers	131		307.7
Feedstocks [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to external customers	131	111	307.7	304.9
Adjusted EBITDA	40.3	45.6	114.3	86.3
Depreciation and amortization	$ 2.9	3.6	$ 8.9	9.2
Americas Styrenics [Member] | Americas Styrenics
Segment Reporting Information [Line Items]
Percentage of ownership underlying net assets	50.00%		50.00%
Americas Styrenics [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Equity in earnings of unconsolidated affiliates	$ 34.5	43.8	$ 113.3	92.2
Adjusted EBITDA	34.5	43.8	113.3	92.2
Investment in unconsolidated affiliates	$ 180.8	$ 161.9	$ 180.8	$ 161.9

Segments - Recon. of Net Income

Segments - Recon. of Net Income to Segment Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Income before income taxes	$ 93.9	$ 41.5	$ 357.8	$ 267.1
Interest expense, net	(10.1)	(18.4)	(35.8)	(55.4)
Depreciation and amortization	31.8	29.2	96	80.1
Corporate Unallocated	20.9	21.8	65.6	70.8
Adjusted EBITDA addbacks	7.1	76.7	18.4	71.2
Adjusted EBITDA	163.8	187.6	573.6	544.6
Loss on extinguishment of long-term debt		65.3	0.2	65.3
Net loss (gain) on disposition of businesses and assets		0.2	(0.5)	(9.7)
Restructuring and other charges	0.9	1.5	2.6	4.8
Acquisition transactions and integration costs	0.1	3.8	0.6	4.9
Asset impairment charges or write-offs		4.3		4.3
Other items	6.1	1.6	15.5	1.6
Operating Segments [Member]
Segment Reporting Information [Line Items]
Income before income taxes	93.9	41.5	357.8	267.1
Corporate Unallocated [Member]
Segment Reporting Information [Line Items]
Interest expense, net	(10.1)	(18.4)	(35.8)	(55.4)
Depreciation and amortization	$ 2.3	$ 2.2	$ 6.8	$ 6.4

Restructuring (Details)

Restructuring (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 1.2	$ 2.1	$ 3.5	$ 6.6
Restructuring Reserve [Roll Forward]
Accrued charges/Balance at beginning of period			2
Expenses			2.3
Payments/Deductions			(2.7)
Accrued charges/Balance at end of period	1.6		1.6
Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.7	1	1.8	2.8
Cumulative life-to-date charges	5.7		5.7
Livorno Plant Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.2	0.8	1	2.3
Cumulative life-to-date charges	24		24
Land held for sale	12.2		12.2
Prepayment received on sale of property			1.3
Deferred taxes on land held for sale	2.9		2.9
Other Restructurings
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.3	0.3	0.7	1.5
Asset Impairment And Accelerated Depreciation [Member] | Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.3	0.6	0.8	1.7
Cumulative life-to-date charges	2.9		2.9
Asset Impairment And Accelerated Depreciation [Member] | Livorno Plant Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Charges			0.4
Cumulative life-to-date charges	14.7		14.7
Accelerated Depreciation On Related Assets [Member] | Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	0.3		0.3
Employee Termination Benefit Charges
Restructuring Reserve [Roll Forward]
Accrued charges/Balance at beginning of period			1.4
Expenses			0.5
Payments/Deductions			(0.9)
Accrued charges/Balance at end of period	1		1
Employee Termination Benefit Charges | Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.1	0.2	0.5	0.3
Cumulative life-to-date charges	0.9		0.9
Employee Termination Benefit Charges | Livorno Plant Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		0.2		0.6
Cumulative life-to-date charges	5.4		5.4
Contract Termination
Restructuring Reserve [Roll Forward]
Accrued charges/Balance at beginning of period			0.6
Accrued charges/Balance at end of period	0.6		0.6
Contract Termination | Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Restructuring Charges				0.6
Cumulative life-to-date charges	0.6		0.6
Contract Termination | Livorno Plant Restructuring
Restructuring Cost and Reserve [Line Items]
Cumulative life-to-date charges	0.3		0.3
Decommissioning and Other Charges
Restructuring Reserve [Roll Forward]
Expenses			1.8
Payments/Deductions			(1.8)
Decommissioning and Other Charges | Terneuzen Plant Modernization
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.3	0.2	0.5	0.2
Cumulative life-to-date charges	1.3		1.3
Expected restructuring charges	0.6		0.6
Decommissioning and Other Charges | Livorno Plant Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.2	$ 0.6	0.6	$ 1.7
Cumulative life-to-date charges	$ 3.6		$ 3.6

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Components (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period			$ 674.8	$ 447.7
Balance at end of period	$ 826.2	$ 572.6	826.2	572.6
Cumulative Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period	(112.7)	(95.8)	(94.5)	(119)
Other comprehensive income (loss)	(4.6)	(1.6)	(22.8)	21.6
Balance at end of period	(117.3)	(97.4)	(117.3)	(97.4)
Pension and Other Postretirement Benefit Plans, Net
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period	(43.8)	(61.3)	(45)	(63.5)
Amounts reclassified from AOCI to net income	0.6	0.8	1.8	3
Balance at end of period	(43.2)	(60.5)	(43.2)	(60.5)
Accumulated Gain Loss Net Cash Flow Hedge Parent [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period	8.6	(5.5)	(6.1)	12.3
Other comprehensive income (loss)	1.6	(6.4)	10.1	(20.7)
Amounts reclassified from AOCI to net income	0.5	2.7	6.7	(0.8)
Balance at end of period	10.7	(9.2)	10.7	(9.2)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at beginning of period	(147.9)	(162.6)	(145.6)	(170.2)
Other comprehensive income (loss)	(3)	(8)	(12.7)	0.9
Amounts reclassified from AOCI to net income	1.1	3.5	8.5	2.2
Balance at end of period	$ (149.8)	$ (167.1)	$ (149.8)	$ (167.1)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Reclassification (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	$ 1,068.1	$ 948.1	$ 3,088.3	$ 2,872.3
Interest expense, net	10.1	18.4	35.8	55.4
Income before income taxes	(93.9)	(41.5)	(357.8)	(267.1)
Provision for (benefit from) income taxes	19.2	8.3	64.5	56.4
Net income	(74.7)	(33.2)	(293.3)	(210.7)
Pension and Other Postretirement Benefit Plans, Net | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Settlement and curtailment gain				0.6
Income before income taxes	0.8	1.2	2.5	4.1
Provision for (benefit from) income taxes	(0.2)	(0.4)	(0.7)	(1.1)
Net income	0.6	0.8	1.8	3
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	(0.2)	(0.5)	(0.7)	(1.4)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net actuarial loss	1	1.7	3.2	4.9
Accumulated Gain Loss Net Cash Flow Hedge Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	0.6	2.7	6.8	(0.8)
Interest expense, net	(0.1)		(0.1)
Income before income taxes	0.5	2.7	6.7	(0.8)
Net income	$ 0.5	$ 2.7	$ 6.7	$ (0.8)

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings:
Net income (loss)	$ 74.7	$ 33.2	$ 293.3	$ 210.7
Shares:
Weighted average ordinary shares outstanding	42.6	43.7	43	43.9
Dilutive effect of RSUs and option awards	0.7	1.1	0.9	1.1
Diluted weighted average ordinary shares outstanding	43.3	44.8	43.9	45
Income (loss) per share:
Income per share- basic	$ 1.75	$ 0.76	$ 6.82	$ 4.80
Income per share- diluted	$ 1.72	$ 0.74	$ 6.68	$ 4.68
Anti-dilutive shares excluded	0.2	0.2	0.2	0.2