v3.4.0.3

Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) $ in Millions	Mar. 31, 2016 USD ($)
Net Capital / Eligible Equity	$ 4,285
Required net capital	513
Excess regulatory capital	3,772
IB LLC [Member]
Net Capital / Eligible Equity	2,618
Required net capital	251
Excess regulatory capital	2,367
TH LLC [Member]
Net Capital / Eligible Equity	342
Required net capital	1
Excess regulatory capital	341
THE [Member]
Net Capital / Eligible Equity	637
Required net capital	202
Excess regulatory capital	435
Other Regulated Operating Companies [Member]
Net Capital / Eligible Equity	688
Required net capital	59
Excess regulatory capital	$ 629

X

- Definition

Eligible equity is equal to the sum of audited capital and reserves and the eligible portion of subordinated debt. Net capital is equal to the net worth of the broker dealer, less certain items such as exchange memberships, carrying value of securities not readily marketable, haircuts on marketable securities in proprietary accounts, furniture and equipment and other illiquid assets as defined.

+ References

No definition available.

+ Details

Name:	ibkr_NetCapitalEligibleEquity
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The amount by which the company's Total Capital exceeds the minimum required for capital adequacy purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_ExcessCapital
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Minimum amount of net capital required to be maintained by the entity to engage in securities transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

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X

- Details

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X

- Details

Name:	ibkr_RegulatoryRequirementsAxis=ibkr_THLLCMember
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X

- Details

Name:	ibkr_RegulatoryRequirementsAxis=ibkr_THEMember
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Data Type:	na
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Period Type:

X

- Details

Name:	ibkr_RegulatoryRequirementsAxis=ibkr_OtherRegulatedOperatingCompaniesMember
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