Represents information pertaining to Common Equity Tier 1 ("CET1")ratio.

No definition available.

Name:	iboc_CommonEquityTierOneRatio
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- Definition

Ratio of tangible equity to average consolidated assets.

+ References

No definition available.

+ Details

Name:	iboc_CommunityBankLeverageRatio
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum amount of assets which will give qualified bank holding companies eligibility for the Federal Reserve's Small Bank Holding Company Policy Statement.

+ References

No definition available.

+ Details

Name:	iboc_MaximumAssetsToExemptBankHoldingCompanies
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- Definition

The maximum amount of assets which will effectively exempt banks that exceed the "community bank leverage ratio" from all risk-based capital requirements.

+ References

No definition available.

+ Details

Name:	iboc_MaximumAssetsToExemptBanks
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Data Type:	xbrli:monetaryItemType
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- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
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- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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- Details

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Capital Requirements (Changes) (Details) - USD ($) $ in Billions	Dec. 31, 2018	Jun. 30, 2018	May 24, 2018	Dec. 31, 2016	Jan. 01, 2016	Jul. 31, 2013
Total Capital (to Risk Weighted Assets), For Capital Adequacy Purposes Ratio (as a percent)				2.50%	0.625%
Maximum amount of assets to exempt banks			$ 10
Maximum amount of assets for qualified bank holding companies	$ 3	$ 1
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent)						6.00%
Minimum
Total Capital (to Risk Weighted Assets), Actual Ratio (as a percent)				4.50%
Community bank leverage ratio			8.00%			4.00%
CET 1 ratio	7.00%
Tier 1 capital (to Risk Weighted Assets), Actual Ratio (as a percent)						4.00%
Maximum
Community bank leverage ratio			10.00%