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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.

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

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'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".

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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".

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

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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".

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Distributions made by IBG LLC to controlling and noncontrolling interests.

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EquityAndEarningsPerShareLineItems

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Fair Value of Issued Shares in Exchange for Membership Interests.

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

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

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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.

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

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Face amount or stated value per share of common stock.

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Amount, before allocation of a valuation allowances, of deferred tax assets attributable to deductible tax credit carryforwards including, but not limited to, research, foreign, general business, alternative minimum tax, and other deductible tax credit carryforwards.

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

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

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

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

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

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Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended	9 Months Ended	12 Months Ended			36 Months Ended	72 Months Ended	156 Months Ended	212 Months Ended
	Jan. 21, 2025	Jul. 25, 2024	Jul. 26, 2023	Oct. 07, 2019	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2010	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	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						$ 196	$ 196	$ 197			$ 196	$ 197	$ 196
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						$ 688	$ 688				$ 688		688
Tax savings owed to IBG Holdings LLC													585
Tax savings retained by IBG Inc.													103
Tax savings paid to IBG Holdings LLC													$ 293
Shares reserved for future issuance														360,000,000
Shares redeemed by IBG Holdings from IBG LLC										5,013,259
Cash Redemptions IBG Holdings										$ 114
Fair Value of Issued Shares in Exchange for Membership Interests		$ 39										$ 1,900
Stock registered, number of common stock			630,000	1,000,000
Distribution from IBG LLC							961	741	$ 533
Cash distribution to IBG, Inc.							246	$ 185	$ 128
Dividend per share					$ 0.10	$ 0.25		$ 0.10	$ 0.10
Dividends paid to common shareholders							$ 92	$ 42	$ 40
Subsequent Event [Member]
Equity And Earnings Per Share [Line Items]
Dividend per share	$ 0.25
Subsequent Event [Member] \| O 2025 Q1 Dividends [Member]
Equity And Earnings Per Share [Line Items]
Declaration Date	Jan. 21, 2025
Payment Date	Mar. 14, 2025
Record Date	Feb. 28, 2025
IBG LLC [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC						25.80%	25.80%				25.80%		25.80%	10.00%
IBG Holdings ownership % of IBG LLC						74.20%	74.20%				74.20%		74.20%	90.00%
IBG LLC [Member] \| Thomas Peterffy And Affiliates [Member]
Equity And Earnings Per Share [Line Items]
Majority stakeholder percentage						91.40%	91.40%				91.40%		91.40%	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
IBKR Promotions [Member]
Equity And Earnings Per Share [Line Items]
Shares Issued											620,000
Member Redemptions [Member]
Equity And Earnings Per Share [Line Items]
Shares Issued		333,000										40,111,445