Capital Requirements (Details)	12 Months Ended
Dec. 31, 2025 USD ($)
Capital Requirements
Dividend payable by subsidiaries, maximum	$ 1,644,000,000

Represents the maximum amount of dividend the subsidiary banks could pay to the entity.

No definition available.

Name:	iboc_MaximumDividendIncomeToBeReceivedFromSubsidiaries
Namespace Prefix:	iboc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration