Total value of shares redeemed by IBG Holdings from IBG LLC funded by using cash on hand at IBG LLC.

No definition available.

Name:	ibkr_CashRedemptions
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Useful life of deferred tax asset related to common stock offerings. This deferred tax asset is amortized as additional deferred income tax expense from the IPO date and from the additional redemption dates.

+ References

No definition available.

+ Details

Name:	ibkr_DTUsefulLife
Namespace Prefix:	ibkr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Cumulative Deferred tax asset arising from Common Stock offerings. This amount represent the cumulative DTA recognize from public offerings excluding and amortization.

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetArisingFromEquityOfferings
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of tax savings retained by the Company according to the "Tax Receivable Agreement"

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetPercentageRetainedByCompany
Namespace Prefix:	ibkr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

'Cumulative amount of tax savings realized by the Company, from the IPO and follow-on offerings, that has been paid to IBG Holdings, LLC according to the "Tax Receivable Agreement".

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetsPaidToHoldings
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cumulative amount of tax savings realized by the Company, from the IPO and follow-on offerings, that is payable to IBG Holdings, LLC according to the "Tax Receivable Agreement".

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetsPayableToHoldings
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percent of tax savings realized by the Company that is payable to Holdings according to the "Tax Receivable Agreement"

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetsPercentagePayableToHoldings
Namespace Prefix:	ibkr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Cumulative amount of tax savings realized by the Company, from the IPO and follow-on offerings, that is retained by the Company according to the "Tax Receivable Agreement".

+ References

No definition available.

+ Details

Name:	ibkr_DeferredTaxAssetsValueNotPayableToCompany
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Distributions made by IBG LLC to controlling and noncontrolling interests.

+ References

No definition available.

+ Details

Name:	ibkr_DividendsPaid
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

EquityAndEarningsPerShareLineItems

+ References

No definition available.

+ Details

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

- Definition

Fair Value of Issued Shares in Exchange for Membership Interests.

+ References

No definition available.

+ Details

Name:	ibkr_FairValueOfIssuedSharesInExchangeForMembershipInterests
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

IBG Holdings LLC's ownership percentage in Class B common stock.

+ References

No definition available.

+ Details

Name:	ibkr_HoldingsOwnershipPercentageClassB
Namespace Prefix:	ibkr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percent ownership of IBG LLC redeemed by IBG Holdings from its members in connection with the consummation of the IPO.

+ References

No definition available.

+ Details

Name:	ibkr_HoldingsRedemptionIBGLLC
Namespace Prefix:	ibkr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Majority Stakeholder Percentage

+ References

No definition available.

+ Details

Name:	ibkr_MajorityStakeholderPercentage
Namespace Prefix:	ibkr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of membership interests redeemed by IBG Holdings, LLC from IBG LLC which were funded using cash on hand at IBG LLC.

+ References

No definition available.

+ Details

Name:	ibkr_ShareRedeemedByIBGHoldings
Namespace Prefix:	ibkr_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Stock Registered During Period Shares, Common Stock

+ References

No definition available.

+ Details

Name:	ibkr_StockRegisteredDuringPeriodSharesCommonStock
Namespace Prefix:	ibkr_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The unamortized balance of the cumulative deferred tax asset arising from Common Stock offerings.

+ References

No definition available.

+ Details

Name:	ibkr_UnamortizedDeferredTaxAssetArisingFromEquityOfferings
Namespace Prefix:	ibkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents disclosure of the total aggregate cash dividends paid to the entity by consolidated subsidiaries, by unconsolidated subsidiaries, and by 50 percent or less owned persons accounted for using the equity method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

+ Details

Name:	us-gaap_CashDividendsPaidToParentCompany
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

+ Details

Name:	us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Face amount or stated value per share of common stock.

+ References

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the declared dividend will be paid, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-3

+ Details

Name:	us-gaap_DividendPayableDateToBePaidDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the dividend to be paid was declared, in YYYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DividendsPayableDateDeclaredDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the holder must own the stock to be entitled to the dividend, in YYYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_DividendsPayableDateOfRecordDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ Details

Name:	us-gaap_PaymentsOfDividendsCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of new stock issued during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-SubTopic 10
-Topic 505
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(4)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(i)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DividendsAxis=ibkr_O2025Q4DividendsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=ibkr_IbgLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ibkr_ThomasPeterffyAndAffiliatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended	3 Months Ended						6 Months Ended	9 Months Ended		36 Months Ended	81 Months Ended	168 Months Ended	221 Months Ended
	Oct. 16, 2025	Jul. 30, 2025	Jul. 26, 2023	Oct. 07, 2019	Mar. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2010	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2025	May 03, 2007
Equity And Earnings Per Share [Line Items]
IBG Holdings Redemption of IBG LLC																			10.00%
IBG Holdings LLC Ownership Percentage of Class B Common Stock																			100.00%
Amortization period DTA (years)													15 years
Unamortized deferred tax asset arising from equity offerings						$ 223						$ 223	$ 223			$ 223	$ 196	$ 223
Percent of tax savings owed to IBG Holdings LLC													85.00%
Percentage of tax savings retained by IBG Inc.													15.00%
Deferred tax asset from common stock offerings																		727
Tax savings owed to IBG Holdings LLC																		618
Tax savings retained by IBG Inc.																		109
Tax savings paid to IBG Holdings LLC																		$ 308
Shares reserved for future issuance						1,440,000,000						1,440,000,000	1,440,000,000			1,440,000,000		1,440,000,000	360,000,000
Shares redeemed by IBG Holdings from IBG LLC															20,053,036
Cash Redemptions IBG Holdings															$ 114
Fair Value of Issued Shares in Exchange for Membership Interests		$ 254															$ 2,000
Stock registered, number of common stock			2,520,000	4,000,000
Shares Issued		3,836,000															161,777,780
Distribution from IBG LLC													$ 918
Cash distribution to IBG, Inc.													238
Dividend per share					$ 0.0625	$ 0.08	$ 0.08	$ 0.0625	$ 0.0625	$ 0.0625	$ 0.025
Dividends paid to common shareholders					$ 27							$ 71	$ 98	$ 65
Subsequent Event [Member]
Equity And Earnings Per Share [Line Items]
Dividend per share	$ 0.08
Subsequent Event [Member] \| O 2025 Q4 Dividends [Member]
Equity And Earnings Per Share [Line Items]
Declaration Date	Oct. 16, 2025
Payment Date	Dec. 12, 2025
Record Date	Dec. 01, 2025
IBG LLC [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC						26.30%						26.30%	26.30%			26.30%		26.30%	10.00%
IBG Holdings ownership % of IBG LLC						73.70%						73.70%	73.70%			73.70%		73.70%	90.00%
Shares Issued																2,880,000
IBG LLC [Member] \| Thomas Peterffy And Affiliates [Member]
Equity And Earnings Per Share [Line Items]
Majority stakeholder percentage						91.60%						91.60%	91.60%			91.60%		91.60%	84.60%
Common Class A [Member]
Equity And Earnings Per Share [Line Items]
Common stock, par value						$ 0.01						$ 0.01	$ 0.01			$ 0.01	$ 0.01	$ 0.01
Common Class B [Member]
Equity And Earnings Per Share [Line Items]
Common stock, par value						$ 0.01						$ 0.01	$ 0.01			$ 0.01	$ 0.01	$ 0.01