v2.4.0.8

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) (USD $) In Millions, unless otherwise specified | Jun. 30, 2014 | Dec. 31, 2013
--- | --- | ---
Permitted To Repledge [Member] |  |  |  |
Collateralized Transactions [Line Items] |  |  |  |
Securities lending transactions | $ 10,023.5 |  | $ 9,331.9 |
Agreements to resell | 6,187.0 | [1] | 7,116.1 | [1]
Customer margin assets | 14,122.6 |  | 11,753.3 |
Total collateralized transactions | 30,333.1 |  | 28,201.3 |
Sold Or Repledged [Member] |  |  |  |
Collateralized Transactions [Line Items] |  |  |  |
Securities lending transactions | 3,170.3 |  | 2,504.3 |
Agreements to resell | 6,183.8 | [1] | 7,099.6 | [1]
Customer margin assets | 5,564.4 |  | 4,602.9 |
Total collateralized transactions | $ 14,918.5 |  | $ 14,206.8 |
[1] | At June 30, 2014, $5.91 billion or 96% (at December 31, 2013, $6.73 billion, or 95%, of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.

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- Definition Market value of collateral received in reverse repurchase transactions + References No definition available. + Details
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Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | ibkr_CollateralizedTransactionsLineItems
Namespace Prefix: | ibkr_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Total market value of collateralized transactions as of the balance sheet date. + References No definition available. + Details
Name: | ibkr_CollateralizedTransactionsTotal
Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Market value of collateral received in securities lending transactions + References No definition available. + Details
Name: | ibkr_SecuritiesLendingCollateralizedTransactions
Namespace Prefix: | ibkr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it is permitted by contract or custom to sell or re-pledge to counterparties as collateral. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729 + Details
Name: | us-gaap_CustomerSecuritiesForWhichEntityHasRightToSellOrRepledgeFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant