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Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Billions | Jun. 30, 2017 | Dec. 31, 2016
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Financial Assets And Financial Liabilities [Abstract] |  |
Securities purchased under agreement to resell segregated for regulatory purposes | $ 13.8 | $ 11.0

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- Definition The carrying value of funds, segregated for regulatory purposes and for the exclusive benefit of customers, outstanding loaned in the form of security resale agreements if the agreement requires the purchaser to resell the identical security purchased or a security that meets the definition of "substantially the same" in the case of a dollar roll. Also includes purchases of participations in pools of securities that are subject to a resale agreement. + References No definition available. + Details
Name: | ibkr_SegregatedSecuritiesPurchasedUnderAgreementsToResell
Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration