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Earnings Per Share - Additional Information (Detail) - shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Earnings per share [abstract] |  |
Potential anti-dilutive preferred shares excluded from calculation of diluted earnings | 538,312 | 13,938,070

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- References No definition available. + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Potential anti-dilutive preferred shares excluded from calculation of diluted earnings + References No definition available. + Details
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Namespace Prefix: | itub_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration