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Equity And Earnings Per Share (IBG LLC Ownership of Member Interests) (Details) | Dec. 31, 2017 shares
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Ownership Percentage | 100.00%
Membership Interests | 411,709,048
IBG Inc [Member] |
Ownership Percentage | 17.40%
Membership Interests | 71,479,604
Holdings [Member] |
Ownership Percentage | 82.60%
Membership Interests | 340,229,444

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- Definition The amount of membership interests in IBG LLC + References No definition available. + Details
Name: | ibkr_MembershipInterests
Namespace Prefix: | ibkr_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition The percent of ownership in IBG LLC membership interests + References No definition available. + Details
Name: | ibkr_OwnershipPercentage
Namespace Prefix: | ibkr_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | ibkr_IbgOwnershipAxis=ibkr_IbgIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ibkr_IbgOwnershipAxis=ibkr_HoldingsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |