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Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended				6 Months Ended		36 Months Ended	42 Months Ended	132 Months Ended	182 Months Ended
	Aug. 01, 2022	Jul. 27, 2020	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2010	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2022	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%
Preferred stock shares authorized			10,000				10,000			10,000	10,000	10,000
Preferred stock shares issued			0				0			0	0	0
Preferred stock shares outstanding			0				0			0	0	0
Amortization period DTA (years)							15 years
Unamortized deferred tax asset arising from equity offerings			$ 193				$ 193			$ 193	$ 209	$ 193
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			$ 634				$ 634			$ 634		634
Tax savings owed to IBG Holdings LLC												539
Tax savings retained by IBG Inc.												95
Tax savings paid to IBG Holdings LLC												$ 243
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											$ 1,500
Stock registered, number of common stock		990,000
Shares Issued	3,271,390									270,000	34,207,307
Shares issued, value	$ 192
Distribution from IBG LLC							302
Cash distribution to IBG, Inc.							$ 71
Dividend per share			$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Dividends paid to common shareholders			$ 11	$ 9			$ 20	$ 18
Declaration Date							Jul. 19, 2022
Payment Date							Sep. 14, 2022
Record Date							Sep. 01, 2022
Subsequent Event [Member] \| Mr. Thomas Peterffy [Member]
Equity And Earnings Per Share [Line Items]
Majority stakeholder percentage	90.50%
IBG LLC [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC			23.70%				23.70%			23.70%		23.70%	10.00%
IBG LLC [Member] \| Holdings [Member]
Equity And Earnings Per Share [Line Items]
IBG Holdings ownership % of IBG LLC													90.00%
IBG LLC [Member] \| Subsequent Event [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC	24.50%
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
Shares authorized			1,000,000,000				1,000,000,000			1,000,000,000	1,000,000,000	1,000,000,000
Common stock, shares issued			99,731,366				99,731,366			99,731,366	98,359,572	99,731,366
Common stock, shares outstanding			99,560,859				99,560,859			99,560,859	98,204,658	99,560,859
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
Shares authorized			100				100			100	100	100
Common stock, shares issued			100				100			100	100	100
Common stock, shares outstanding			100				100			100	100	100