v3.4.0.3

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Permitted To Repledge [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		$ 10,094	$ 12,131
Agreements to resell	[1]	2,256	757
Customer margin assets		18,991	14,905
Total collateralized transactions		31,341	27,793
Sold Or Repledged [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		2,208	2,229
Agreements to resell	[1]	2,249	743
Customer margin assets		6,714	6,279
Total collateralized transactions		$ 11,171	$ 9,251
[1] As of March 31, 2016, $1.4 billion or 64% (as of December 31, 2015, $0.6 billion or 76%) of securities acquired through agreements to resell that are shown as repledged have been deposited in a separate bank account for the exclusive benefit of customers in accordance with SEC Rule 15c3-3.

X

- Definition

Market value of collateral received in reverse repurchase transactions

+ References

No definition available.

+ Details

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

X

- Definition

Collateralized Transactions [Line Items]

+ References

No definition available.

+ Details

Name:	ibkr_CollateralizedTransactionsLineItems
Namespace Prefix:	ibkr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Total market value of collateralized transactions as of the balance sheet date.

+ References

No definition available.

+ Details

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

X

- Definition

Market value of collateral received in securities lending transactions

+ References

No definition available.

+ Details

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

X

- Definition

Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it is permitted by contract or custom to sell or re-pledge to counterparties as collateral.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

Name:	us-gaap_CustomerSecuritiesForWhichEntityHasRightToSellOrRepledgeFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_StatementScenarioAxis=ibkr_PermittedToRepledgeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementScenarioAxis=ibkr_RepledgedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: