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Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Millions | 9 Months Ended |
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Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015
Financial Assets And Financial Liabilities [Abstract] |  |  |
Transfers of financial instruments sold, but not yet purchased from level 3 to level 1 |  | $ 1 |
Transfers of financial instruments sold, but not yet purchased from level 1 to level 3 | $ 1 |  |
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes | $ 7,000 |  | $ 600

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- Definition Fair Value Liabilities Level 1 To Level 2 Amount + References No definition available. + Details
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Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Transfers of financial liabilities from level 3 to level 1 + References No definition available. + Details
Name: | ibkr_FairValueLiabilitiesLevel3ToLevel1Amount
Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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