v3.26.1
CONDENSED COMBINED DEBTOR-IN-POSSESSION FINANCIAL INFORMATION - Debtors' Balance Sheet (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Dec. 31, 2025
Jun. 30, 2025
Mar. 31, 2025
Dec. 31, 2024
Current assets            
Cash and cash equivalents $ 181.4   $ 146.7 $ 137.0    
Accounts receivable, net of allowances (June 30, 2026: $0.6) 477.4   364.5      
Inventories 390.7   316.0      
Other current assets 116.4   37.5      
Total current assets 1,165.9   864.7      
Investments in unconsolidated affiliate 210.2   206.9 224.0    
Property, plant and equipment, net of accumulated depreciation (June 30, 2026: $220.5) 492.0   523.6      
Other assets            
Goodwill 65.7   67.7      
Other intangible assets, net 444.0   492.9      
Right-of-use assets - operating, net 59.4   56.2      
Deferred charges and other assets 58.8   66.1      
Total other assets 630.5   685.0      
Total assets 2,498.6   2,280.2      
Current liabilities            
Short-term borrowings and current portion of long-term debt 589.6   212.9      
Accounts payable 231.3   283.9      
Current lease liabilities - operating 7.0   11.6      
Income taxes payable 4.4   3.7      
Accrued expenses and other current liabilities 166.9   202.6      
Total current liabilities 999.2   714.7      
Noncurrent liabilities            
Long-term debt, net of unamortized deferred financing fees 1.9   2,332.5      
Noncurrent lease liabilities - operating 26.0   47.9      
Deferred income tax liabilities 29.8   30.5      
Other noncurrent obligations 226.6   252.4      
Total noncurrent liabilities 284.3   2,663.3      
Liabilities subject to compromise 2,562.3          
Commitments and contingencies (Note 13)        
Shareholders' equity (deficit)            
Total shareholders' equity (deficit) (1,347.2) $ (1,222.9) (1,097.8) $ (750.3) $ (679.2) $ (619.9)
Total liabilities and shareholders' equity (deficit) $ 2,498.6   $ 2,280.2      
Trinseo PLC and certain direct and indirect subsidiaries            
CONDENSED COMBINED DEBTOR-IN-POSSESSION FINANCIAL INFORMATION            
Reorganization, Chapter 11, Debtor-in-Possession, All Entities [true false] false          
Current assets            
Cash and cash equivalents $ 60.2          
Accounts receivable, net of allowances (June 30, 2026: $0.6) 42.2          
Inventories 134.5          
Due from affiliates 2,701.1          
Other current assets 70.1          
Total current assets 3,008.1          
Property, plant and equipment, net of accumulated depreciation (June 30, 2026: $220.5) 158.4          
Other assets            
Other intangible assets, net 259.2          
Right-of-use assets - operating, net 25.2          
Deferred charges and other assets 37.7          
Total other assets 322.1          
Total assets 3,488.6          
Current liabilities            
Short-term borrowings and current portion of long-term debt 443.2          
Accounts payable 72.5          
Income taxes payable 0.4          
Accrued expenses and other current liabilities 45.4          
Total current liabilities 561.5          
Noncurrent liabilities            
Deferred income tax liabilities 17.5          
Other noncurrent obligations 22.7          
Total noncurrent liabilities 40.2          
Liabilities subject to compromise 2,562.3          
Commitments and contingencies (Note 13)          
Shareholders' equity (deficit)            
Total shareholders' equity (deficit) 324.6          
Total liabilities and shareholders' equity (deficit) $ 3,488.6