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Collateralized Transactions (Financial instruments owned and pledged where the counterparty has the right to repledge) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Disclosure Collateralized Transactions [Abstract]
Stocks	$ 150	$ 121
U.S. and foreign government securities	39	67
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$ 189	$ 188

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- References

No definition available.

+ Details

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- Definition

Fair value of stocks held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions where counterparty has the right to re-pledge such.

+ References

No definition available.

+ Details

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Namespace Prefix:	ibkr_
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Balance Type:	debit
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- Definition

Fair value of U.S. and foreign government obligations held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions where counterparty has the right to re-pledge such.

+ References

No definition available.

+ Details

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X

- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions where counterparty has the right to re-pledge such.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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