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Financial Assets at Amortized Cost-Securities - Summary of Financial Assets at Amortized Cost - Securities (Parenthetical) (Detail) - BRL (R$) R$ in Millions	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Financial Assets [Line Items]
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients		R$ 33,848	R$ 27,469
Brazilian government securities [member]
Disclosure of Financial Assets [Line Items]
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients		24,988	26,953
Classification of Debt Securities from Fair Value Through Profit or Loss to amortized cost	R$ 3,707
Classification of Debt Securities from Fair Value Through Other Comprehensive Income to amortized cost	8,678
Debt securities at fair value	11,880
Reclassification adjustment of debt securities at fair value	R$ (282)
Government securities - abroad [member]
Disclosure of Financial Assets [Line Items]
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients			479
Corporate securities [member]
Disclosure of Financial Assets [Line Items]
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients		R$ 8,860	R$ 37

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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The fair value of financial assets reclassified out of the fair value through profit or loss category into amortised cost or fair value through other comprehensive income category. [Refer: Financial assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2018-01-01
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-IssueDate 2017-01-01
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The fair value of financial assets reclassified out of the fair value other comprehensive income category so that they are measured at amortised cost. [Refer: Financial assets]

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-Note Effective 2018-01-01
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The fair value of financial assets. [Refer: At fair value [member]; Financial assets]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-IssueDate 2017-01-01
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The amount of financial assets that the entity has pledged as collateral for liabilities or contingent liabilities, including amounts that have been reclassified in accordance with paragraph 3.2.23(a) of IFRS 9. [Refer: Contingent liabilities [member]; Financial assets]

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The amount of reclassification adjustments related to financial assets measured at fair value through other comprehensive income, net of tax. Reclassification adjustments are amounts reclassified to profit (loss) in the current period that were recognised in other comprehensive income in the current or previous periods. [Refer: Financial assets measured at fair value through other comprehensive income; Other comprehensive income]

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