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Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) $ in Millions	Sep. 30, 2018 USD ($)
Net Capital / Eligible Equity	$ 6,268
Required net capital	735
Excess regulatory capital	5,533
IB LLC [Member]
Net Capital / Eligible Equity	4,699
Required net capital	514
Excess regulatory capital	4,185
TH LLC [Member]
Net Capital / Eligible Equity	206
Excess regulatory capital	206
IBKRFS [Member]
Net Capital / Eligible Equity	590
Required net capital	89
Excess regulatory capital	501
Other Regulated Operating Companies [Member]
Net Capital / Eligible Equity	773
Required net capital	132
Excess regulatory capital	$ 641

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

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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=84167132&loc=SL5958568-112826

+ Details

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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

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- Details

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- Details

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X

- Details

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X

- Details

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