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

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

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

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Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions						3 Months Ended		36 Months Ended	87 Months Ended	180 Months Ended	227 Months Ended
	Jun. 12, 2026	Jun. 01, 2026	Apr. 21, 2026	Jul. 26, 2023	Oct. 07, 2019	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2010	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2026	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%
Common stock, par value						$ 0.01			$ 0.01	$ 0.01	$ 0.01
Amortization period DTA (years)						15 years
Unamortized deferred tax asset arising from equity offerings						$ 217			$ 217	$ 222	$ 217
Percent of tax savings owed to IBG Holdings LLC						85.00%
Percentage of tax savings retained by IBG Inc.						15.00%
Deferred Tax Asset Arising From Equity 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	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										$ 2,200
Stock registered, number of common stock				2,520,000	4,000,000
Shares Issued										165,613,780
Distribution from IBG LLC						$ 413
Distribution to IBG, Inc						$ 108
Dividend per share						$ 0.08	$ 0.0625
Dividends paid to common shareholders						$ 36	$ 27
Subsequent Event [Member] \| O 2025 Q2 Dividends [Member]
Equity And Earnings Per Share [Line Items]
Payment Date	Jun. 12, 2026
Record Date		Jun. 01, 2026
IBG LLC [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC						26.30%			26.30%		26.30%	10.00%
IBG Holdings ownership % of IBG LLC						73.70%			73.70%		73.70%	90.00%
Shares Issued									3,080,000
IBG LLC [Member] \| Thomas Peterffy And Affiliates [Member]
Equity And Earnings Per Share [Line Items]
Majority stakeholder percentage						91.60%			91.60%		91.60%	84.60%
Common Class A [Member]
Equity And Earnings Per Share [Line Items]
Common stock, par value						$ 0.01			$ 0.01		$ 0.01
Minimum [Member] \| Subsequent Event [Member]
Equity And Earnings Per Share [Line Items]
Dividend per share			$ 0.08
Maximum [Member] \| Subsequent Event [Member]
Equity And Earnings Per Share [Line Items]
Dividend per share			$ 0.0875