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Loans, Financings and Debentures - Summary of Guarantees of the Debtor Balance on Loans and Financings (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of detailed information about borrowings [line items] |  |
Borrowings | R$ 14,398 | R$ 15,179
Shares [member] |  |
Disclosure of detailed information about borrowings [line items] |  |
Borrowings | 1,390 |
Without Guarantee [member] |  |
Disclosure of detailed information about borrowings [line items] |  |
Borrowings | 195 |
Financial guarantee contracts [member] | Promissory Notes And Sureties [member] |  |
Disclosure of detailed information about borrowings [line items] |  |
Borrowings | 8,850 |
Financial guarantee contracts [member] | Receivables [member] |  |
Disclosure of detailed information about borrowings [line items] |  |
Borrowings | R$ 3,963 |

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