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Equity And Earnings Per Share (IBG LLC Ownership of Member Interests) (Details)	Mar. 31, 2018 shares
Ownership Percentage	100.00%
Membership Interests	411,710,580
IBG Inc [Member]
Ownership Percentage	17.40%
Membership Interests	71,481,136
Holdings [Member]
Ownership Percentage	82.60%
Membership Interests	340,229,444

X

- 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

X

- 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

X

- 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: