v3.25.3
Investments - Investments in Associates and Joint Ventures (Details)
 1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Aug. 31, 2025
BRL (R$)
Sep. 30, 2025
BRL (R$)
Sep. 30, 2024
BRL (R$)
Sep. 30, 2025
BRL (R$)
Sep. 30, 2025
BRL (R$)
€ / shares
Sep. 30, 2024
BRL (R$)
Sep. 30, 2024
BRL (R$)
€ / shares
Dec. 31, 2024
BRL (R$)
Dec. 31, 2023
BRL (R$)
Disclosure of joint ventures [line items]                  
Equity   R$ 45,258,425,000 R$ 41,601,758,000 R$ 45,258,425,000 R$ 45,258,425,000 R$ 41,601,758,000 R$ 41,601,758,000 R$ 32,415,575,000 R$ 44,810,300,000
Income (expenses) of the period   1,961,387,000 3,237,351,000 R$ 13,321,518,000   (308,134,000)      
%       100.00%       100.00%  
In the income (expenses) for the period       R$ (239,671,000)   (14,842,000)      
Goodwill   189,846,000   189,846,000 189,846,000     R$ 225,486,000  
Total Investments, including Goodwill and Financial Instruments   1,417,377,000   1,417,377,000 1,417,377,000     1,816,923,000  
Realization of exchange variation on investments abroad   (15,636,000)        
Impairment loss (reversal of impairment loss) recognised in profit or loss       88,871,000        
Other Operating Income (Expense) from Disposal of Property, Plant and Equipment and Biological Assets       272,228,000   132,693,000      
Associate | Foreign countries                  
Disclosure of joint ventures [line items]                  
Investments Accounted for Using Equity Method, Excluding Goodwill   55,434,000   55,434,000 55,434,000     125,316,000  
In the income (expenses) for the period       R$ (62,334,000)   (21,865,000)      
Ensyn Corporation | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       24.80%          
Investments Accounted for Using Equity Method, Excluding Goodwill   (5,187,000)   R$ (5,187,000) (5,187,000)     2,000  
In the income (expenses) for the period       (20,213,000)   (2,289,000)      
Spinnova Plc                  
Disclosure of joint ventures [line items]                  
Goodwill   189,846,000   189,846,000 189,846,000     225,486,000  
Impairment loss (reversal of impairment loss) recognised in profit or loss       R$ (63,634,000)          
Spinnova Plc | Component Of Other Operating Expenses Related To SPA ClosingConditions                  
Disclosure of joint ventures [line items]                  
Other Operating Income (Expense) from Disposal of Property, Plant and Equipment and Biological Assets R$ (28,679)                
Spinnova Plc | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       18.76%          
Investments Accounted for Using Equity Method, Excluding Goodwill   52,479,000   R$ 52,479,000 52,479,000     95,254,000  
In the income (expenses) for the period       R$ (40,714,000)   (19,576,000)      
Simplifyber, Inc. (Indirect) | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       13.91%          
Investments Accounted for Using Equity Method, Excluding Goodwill   7,605,000   R$ 7,605,000 7,605,000     30,060,000  
In the income (expenses) for the period       R$ (1,407,000)        
Allotrope Energy Ltd [Member] | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       20.00%          
Investments Accounted for Using Equity Method, Excluding Goodwill   537,000   R$ 537,000 537,000        
Joint ventures                  
Disclosure of joint ventures [line items]                  
Investments Accounted for Using Equity Method, Excluding Goodwill   209,756,000   209,756,000 209,756,000     328,055,000  
In the income (expenses) for the period       R$ (113,703,000)   7,023,000      
Biomas | Country of domicile                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       16.66%          
Investments Accounted for Using Equity Method, Excluding Goodwill   5,802,000   R$ 5,802,000 5,802,000     2,923,000  
In the income (expenses) for the period       R$ (4,618,000)   (3,431,000)      
Ibema Companhia Brasileira de Papel | Country of domicile                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       49.90%          
Investments Accounted for Using Equity Method, Excluding Goodwill   198,476,000   R$ 198,476,000 198,476,000     193,901,000  
In the income (expenses) for the period       R$ 13,410,000   27,904,000      
F&E Technologies LLC | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       50.00%          
Investments Accounted for Using Equity Method, Excluding Goodwill   5,478,000   R$ 5,478,000 5,478,000     6,378,000  
In the income (expenses) for the period              
Woodspin Oy                  
Disclosure of joint ventures [line items]                  
Share Of Profit Loss Of Investments Accounted For Using Equity Method       R$ (117,848,000)          
Woodspin Oy | Foreign countries                  
Disclosure of joint ventures [line items]                  
Participation equity (%)       50.00%          
Investments Accounted for Using Equity Method, Excluding Goodwill         124,853,000  
In the income (expenses) for the period       (122,495,000)   (17,450,000)      
Total other investments evaluated at fair value                  
Disclosure of joint ventures [line items]                  
In the income (expenses) for the period              
Non-current financial assets at fair value through other comprehensive income   962,341,000   R$ 962,341,000 962,341,000     1,138,066,000  
Bem Agro Integração e Desenvolvimento S.A. (Indirect)                  
Disclosure of joint ventures [line items]                  
%       5.82%          
Bem Agro Integração e Desenvolvimento S.A. (Indirect) | Country of domicile                  
Disclosure of joint ventures [line items]                  
Non-current financial assets at fair value through other comprehensive income   3,461,000   R$ 3,461,000 3,461,000     4,026,000  
Celluforce Inc. (Direct)                  
Disclosure of joint ventures [line items]                  
%       8.28%          
Celluforce Inc. (Direct) | Foreign countries                  
Disclosure of joint ventures [line items]                  
Non-current financial assets at fair value through other comprehensive income   24,681,000   R$ 24,681,000 24,681,000     27,823,000  
Nfinite Nanotechnology Inc. (Indirect)                  
Disclosure of joint ventures [line items]                  
%       4.90%          
Nfinite Nanotechnology Inc. (Indirect) | Foreign countries                  
Disclosure of joint ventures [line items]                  
Non-current financial assets at fair value through other comprehensive income   5,452,000   R$ 5,452,000 5,452,000     6,347,000  
Lenzing Aktiengesellschaft (Indirect)                  
Disclosure of joint ventures [line items]                  
%       15.00%          
Lenzing Aktiengesellschaft (Indirect) | Foreign countries                  
Disclosure of joint ventures [line items]                  
Non-current financial assets at fair value through other comprehensive income   928,747,000   R$ 928,747,000 928,747,000     1,099,870,000  
Total Goodwill                  
Disclosure of joint ventures [line items]                  
Goodwill   189,846,000   189,846,000 189,846,000     R$ 225,486,000  
Impairment loss (reversal of impairment loss) recognised in profit or loss       (63,634,000)          
Ensyn Corporation                  
Disclosure of joint ventures [line items]                  
Equity   (20,917,000)   (20,917,000) (20,917,000)        
Income (expenses) of the period       (76,085,000)          
Spinnova Plc                  
Disclosure of joint ventures [line items]                  
Equity   279,740,000   279,740,000 R$ 279,740,000        
Income (expenses) of the period       (217,242,000)          
NASDAQ, Nordic Growth Market, Average Share Price | € / shares         R$ 0.61   R$ 0.95    
Biomas | Country of domicile                  
Disclosure of joint ventures [line items]                  
Equity   34,828,000   34,828,000 R$ 34,828,000        
Income (expenses) of the period       (29,371,000)          
Ibema Companhia Brasileira de Papel | Country of domicile                  
Disclosure of joint ventures [line items]                  
Equity   397,748,000   397,748,000 397,748,000        
Income (expenses) of the period       26,873,000          
F&E Technologies LLC | Foreign countries                  
Disclosure of joint ventures [line items]                  
Equity   10,956,000   10,956,000 10,956,000        
Income (expenses) of the period                
Woodspin Oy | Foreign countries                  
Disclosure of joint ventures [line items]                  
Equity   234,894,000   234,894,000 234,894,000        
Income (expenses) of the period       (26,427,000)          
Simplifyber, Inc. (Indirect)                  
Disclosure of joint ventures [line items]                  
Equity   R$ 54,672,000   54,672,000 R$ 54,672,000        
Income (expenses) of the period       R$ (10,115,000)