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Securities - Schedule of Cash Investments (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of investment securities [Line Items] |  |
Current investments | R$ 1,058 | R$ 1,014
Non-current investments | 30 | 31
Investments | 1,088 | 1,045
Bank certificates of deposit [member] |  |
Disclosure of investment securities [Line Items] |  |
Current investments | 3 | 46
Financial Notes-Banks [member] |  |
Disclosure of investment securities [Line Items] |  |
Current investments | 303 | 728
Non-current investments |  | 14
Treasury financial notes (LFTs) [member] |  |
Disclosure of investment securities [Line Items] |  |
Current investments | 740 | 193
Debentures [member] |  |
Disclosure of investment securities [Line Items] |  |
Current investments | 11 | 45
Non-current investments | 30 | 17
Other [member] |  |
Disclosure of investment securities [Line Items] |  |
Current investments | R$ 1 | R$ 2

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