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Financial Instruments - Option embedded in Promissory Note (Detail) R$ in Millions, $ in Millions, $ in Millions |  |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 06, 2019 BRL (R$) | Dec. 06, 2019 USD ($) | Dec. 06, 2016 BRL (R$) | Sep. 30, 2020 | Dec. 31, 2019 MXN ($) | Dec. 31, 2020 MXN ($)
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Borrowings | $ |  |  |  |  | $ 114,016 | $ 184,196
Promissory notes paid | R$ 1,002 | $ 236 |  |  | $ 4,670 |
Spal [member] | Vonpar [member] | Notes payable [member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Borrowings Term |  |  | 3 years |  |  |
Borrowings | R$ |  |  | R$ 1,166 |  |  |
Borrowings, interest rate |  |  | 0.375% |  |  |
Estrella Azul [Member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Proportion of ownership interest sold |  |  |  | 100.00% |  |

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