Financial risk management - Market risk, value at risk (Details) - BRL (R$) R$ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Disclosure of nature and extent of risks arising from financial instruments [line items]
Confidence level	99.00%
Holding period	21 days
Number of workdays	0 days
Minimum
Disclosure of nature and extent of risks arising from financial instruments [line items]
Number of workdays	94 days
Maximum
Disclosure of nature and extent of risks arising from financial instruments [line items]
Number of workdays	252 days
Trading Book
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	R$ 6,645	R$ 39,861
Diversification effects (correlation)	1,758	17,939
Value-at-Risk	4,887	21,921
Trading Book \| Price index coupons
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	4,882	4,262
Trading Book \| Pre fixed interest rate
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	83	6,319
Trading Book \| Foreign currency coupons
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor		365
Trading Book \| Exchange rate
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	80	2,014
Trading Book \| Shares prices
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	1,599	4,056
Trading Book \| Others
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor		22,845
Banking Book
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	452,045	191,893
Diversification effects (correlation)	84,587	18,491
Value-at-Risk	367,458	173,402
Banking Book \| Price index coupons
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	364,502	169,917
Banking Book \| Pre fixed interest rate
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	49,577	20,345
Banking Book \| Interest rate Coupons
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	36,555	1,631
Banking Book \| Shares prices
Disclosure of nature and extent of risks arising from financial instruments [line items]
Risk Factor	R$ 1,412	R$ 20,345

Represents the diversification effects (correlation).

No definition available.

Name:	b3_VarCalculationDiversificationEffectsCorrelation
Namespace Prefix:	b3_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the holding period.

+ References

No definition available.

+ Details

Name:	b3_VarCalculationHoldingPeriod
Namespace Prefix:	b3_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of workdays.

+ References

No definition available.

+ Details

Name:	b3_VarCalculationNumberOfWorkdays
Namespace Prefix:	b3_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the risk factor.

+ References

No definition available.

+ Details

Name:	b3_VarCalculationRiskFactor
Namespace Prefix:	b3_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The confidence level used to determine the risk adjustment for non-financial risk. [Refer: Risk adjustment for non-financial risk [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2023-01-01
-Name IFRS
-Number 17
-IssueDate 2021-01-01
-Paragraph 119
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=17&code=ifrs-tx-2021-en-r&anchor=para_119&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_ConfidenceLevelUsedToDetermineRiskAdjustmentForNonfinancialRisk
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The measure of a potential loss exposure as a result of future market movements, based on a specified confidence interval and measurement horizon.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 7
-IssueDate 2021-01-01
-Paragraph 41
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2021-en-r&anchor=para_41&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_ValueAtRisk
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=b3_TradingBookMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorPriceIndexCouponsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorPreFixedInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorForeignCurrencyCouponsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorExchangeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorSharesPricesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorOthersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=b3_BankingBookMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RiskExposuresAxis=b3_RiskFactorInterestRateCouponsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: