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Post-Employment Obligation - Additional Information (Detail) - BRL (R$)
R$ in Millions
 1 Months Ended 12 Months Ended
Mar. 28, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of defined benefit plans [line items]        
Obligation for past actuarial deficits relating to pension fund   R$ 652 R$ 721  
Obligation for past actuarial deficits amortization description   Will be amortized until June of 2024, through monthly installments calculated by the system of constant installments (known as the 'Price' table), and adjusted by the IPCA (Expanded National Customer Price) inflation index (published by the Brazilian Geography and Statistics Institute - IBGE) plus 6% per year    
Obligation rate for actuarial assumption   6.00%    
Percentage insured reduction of post-employment obligations     20.00%  
Changes in reduction of post-employment obligations     R$ 619  
Reduction of post-employment obligations period     5-year  
Costs of post-employment obligations   R$ 68 R$ 65 R$ 103
Financial costs and monetary updating expence   68 65 103
Entering into significant commitments or contingent liabilities [member]        
Disclosure of defined benefit plans [line items]        
deficit found in Plan R$ 178      
Monthly installments 167 monthly installments      
Forluz pension [member]        
Disclosure of defined benefit plans [line items]        
Retirement benefits plan   R$ 378 283  
Remuneratory interest   6.00%    
Pension Funds [member]        
Disclosure of defined benefit plans [line items]        
Expected employer contributions   R$ 184    
Defined contribution plan [member]        
Disclosure of defined benefit plans [line items]        
Expected employer contributions   82    
Post Employment Benefit Obligations [member]        
Disclosure of defined benefit plans [line items]        
Costs of post-employment obligations   R$ 337 R$ 391 R$ 345