Income taxes - Additional information (Details) - BRL (R$)	Jun. 30, 2026	Dec. 31, 2025
Possible losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	R$ 10,057,925,000	R$ 4,559,801,000
Possible losses \| Income tax assessment - Foreign Earnings - Brazil-Austria Tax Treaty (2021) \| Tax contingent liability
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	5,176,100,000	5,106,344,000
Possible losses \| Income tax assessment - Exchange of Industrial and Forestry Assets (2007) \| Tax contingent liability
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	1,979,365,000	1,861,899,000
Possible losses \| Income tax assessment - Non-deductible Expenses, Operating Expense Deductions, Foreign Subsidiary Earnings, Goodwill Amortization, Directors' Bonuses and Tax Loss Carryforwards (2019) \| Tax contingent liability
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	1,053,991,000	1,008,823,000
Possible losses \| Income tax assessment - Disallowance of Depreciation, Amortization and Depletion Expenses (2010) \| Tax contingent liability
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	960,921,000	931,979,000
Possible losses \| Income tax assessment - Recalculation of Foreign Subsidiary Profits (2014-2016) \| Tax contingent liability
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Possible losses for which no provision was recorded	690,658,000	663,188,000
Probable losses \| Tax assessment - Corporate Income Tax and Social Contribution
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Other provisions	1,822,000	1,749,000
Other provisions	R$ 1,822,000	R$ 1,749,000