Interactive Brokers (IBKR) 10-Q 9 Aug 16 2016 Q2 Quarterly report Financial data

Documentation and Entity Inform

Documentation and Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Aug. 09, 2016
Entity Registrant Name	Interactive Brokers Group, Inc.
Entity Central Index Key	1,381,197
Document Type	10-Q
Document Period End Date	Jun. 30, 2016
Amendment Flag	false
Fiscal Year Focus	2,016
Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Common Class A
Common Stock Shares Outstanding		67,267,845
Common Class B
Common Stock Shares Outstanding		100

Condensed Consolidated Statemen

Condensed Consolidated Statements of Financial Condition - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 1,443	$ 1,601
Cash and securities segregated for regulatory purposes	25,257	21,309
Securities Borrowed	3,760	3,924
Securities purchased under agreements to resell	113	195
Financial instruments owned, at fair value:
Financial instruments owned	2,580	1,987
Financial instruments owned and pledged as collateral	1,674	1,433
Total financial instruments owned, at fair value	4,254	3,420
Receivables:
Customers receivables	15,137	17,050
Receivables from brokers, dealers and clearing organizations	1,351	692
Interest receivable	58	63
Total receivables	16,546	17,805
Other Assets	456	480
Total assets	51,829	48,734
Liabilities and equity
Short-term borrowings	8
Securities Loaned	3,270	2,894
Financial instruments sold, not yet purchased, at fair value	2,874	2,617
Payables:
Payables to customer	39,319	37,084
Payables to brokers, dealers and clearing organizations	286	423
Affiliate	274	291
Accounts payable, accrued expenses and other liabilities	102	78
Interest payable	4	3
Total payables	39,985	37,879
Total liabilities	46,137	43,390
Stockholders' equity:
Additional paid-in capital	746	718
Retained earnings	192	145
Accumulated other comprehensive income, net of income taxes of $0 and $0 as of June 30, 2016 and December 31, 2015	5	2
Treasury stock, at cost, 844,715 and 135,815 shares as of June 30, 2016 and December 31, 2015	(29)	(3)
Total stockholders' equity	915	863
Noncontrolling interests	4,777	4,481
Total equity	5,692	5,344
Total liabilities and stockholders' equity	51,829	48,734
Common Class A
Stockholders' equity:
Common stock	1	1
Common Class B
Stockholders' equity:
Common stock

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 99	$ 130
Accumulated Other Comprehensive Income, Tax	$ 0	$ 0
Treasury stock shares	844,715	135,815
Common Class A
Common stock, par value	$ 0.01	$ 0.01
Shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	66,516,360	64,121,150
Common stock, shares outstanding	65,671,645	63,985,335
Common Class B
Shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Trading gains	$ 34	$ 67	$ 86	$ 129
Commissions and execution fees	152	157	318	306
Interest income	144	126	289	234
Other income (loss)	57	55	201	(77)
Total revenues	387	405	894	592
Interest expense	18	18	36	33
Total net revenues	369	387	858	559
Non-interest expenses:
Execution and clearing	59	59	121	114
Employee compensation and benefits	58	58	116	115
Occupancy, depreciation and amortization	13	11	25	21
Communications	9	7	16	13
General and administrative	14	13	27	29
Customer bad debt	3	(1)	3	138
Total non-interest expenses	156	147	308	430
Income before Income Taxes	213	240	550	129
Income tax expense	13	19	40	17
Net income	200	221	510	112
Less net income attributable to noncontrolling interests	173	198	450	102
Net income available for common stockholders	$ 27	$ 23	$ 60	$ 10
Earnings per share:
Basic	$ 0.41	$ 0.38	$ 0.93	$ 0.17
Diluted	$ 0.40	$ 0.37	$ 0.91	$ 0.17
Weighted average common shares outstanding:
Weighted Average Number of Shares Outstanding, Basic	64,967,364	59,481,778	64,476,421	58,980,348
Weighted Average Number of Shares Outstanding, Diluted	66,470,913	61,038,926	65,863,408	60,436,914
Comprehensive income:
Net income available for common stockholders	$ 27	$ 23	$ 60	$ 10
Other comprehensive income:
Cumulative translation adjustment, before income taxes	(3)	4	3	3
Other comprehensive income (loss), net of tax	(3)	4	3	3
Comprehensive income available for common stockholders	24	27	63	13
Comprehensive income attributable to noncontrolling interests:
Net income attributable to noncontrolling interests	173	198	450	102
Other comprehensive income (loss) - cumulative translation adjustment	(16)	24	17	15
Comprehensive income attributable to noncontrolling interests	$ 157	$ 222	$ 467	$ 117

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 510	$ 112
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Deferred income taxes	18	2
Depreciation and amortization	12	11
Employee stock plan compensation	22	24
Unrealized loss (gain) on other investments, net	7	(15)
Bad debt expense	3	138
Change in operating assets and liabilities:
Decrease in Cash and securities - segregated for regulatory purposes	(3,948)	(1,345)
Increase in securities borrowed	164	826
Securities purchased under agreements to resell	82	238
Financial instruments owned, at fair value	(869)	321
Receivables from customers	1,910	(2,089)
Other receivables	(654)	(87)
(Decrease) increase in other assets	(4)	17
Increase (decrease) in securities loaned	376	(58)
Financial instruments sold but not yet purchased, at fair value	266	(378)
Payable to customers	2,235	2,041
(Decrease) increase in other payables	(118)	143
Net cash provided by (used in) operating activities	12	(99)
Cash flows from investing activities:
Purchases of other investments	(6)	(36)
Distributions received and proceeds from sales of other investments	38	39
Purchase of property and equipment	(14)	(20)
Net cash (used in) provided by investing activities	18	(17)
Cash flows from financing activities:
Short-term borrowings, net	8	(25)
Dividends paid to stockholders	(13)	(12)
Distributions to noncontrolling interests	(160)	(69)
Excess tax benefit on stock incentive plans		1
Repurchases of common stock for employee tax withholding under stock incentive plans	(26)	(25)
Payments made under the Tax Receivable Agreement	(17)
Net cash used in financing activities	(208)	(130)
Effect of exchange rate changes on cash and cash equivalents	20	18
Net decrease in cash and cash equivalents	(158)	(228)
Cash and cash equivalents at beginning of period	1,601	1,269
Cash and cash equivalents at end of period	1,443	1,041
Supplemental disclosures of cash flow information:
Cash paid for interest	35	32
Cash paid for taxes, net	6	17
Non-cash financing activities:
Adjustments to additional paid-in capital for changes in proportionate ownership in IBG LLC	25	27
Adjustments to noncontrolling interests for changes in proportionate ownership in IBG LLC	(25)	$ (27)
Non-cash distribution to noncontrolling interests	$ (5)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Total Stockholders' Equity [Member]	Non-controlling Interests [Member]	Total
Balance at Dec. 31, 2014	$ 1	$ 635	$ (3)	$ 121	$ 12	$ 766	$ 4,419	$ 5,185
Common stock, shares issued at Dec. 31, 2014	58,612,245
Common Stock distributed pursuant to stock incentive plans (in shares)	2,461,632
Compensation for stock grants vesting in the future		4				4	20	24
Excess Tax Benefit On Stock Incentive Plan		1				1		1
Repurchase of common stock for employee tax withholding under stock incentive plans			(25)			(25)		(25)
Dividends paid to stockholders				(12)		(12)		(12)
Distributions from IBG LLC to noncontrolling interests							(69)	(69)
Adjustments for changes in proportionate ownership in IBG LLC		27				27	(27)
Comprehensive Income				10	3	13	117	130
Balance at Jun. 30, 2015	$ 1	667	(28)	119	15	774	4,460	5,234
Common stock, shares issued at Jun. 30, 2015	61,073,877
Balance at Dec. 31, 2015	$ 1	718	(3)	145	2	863	4,481	5,344
Common stock, shares issued at Dec. 31, 2015	64,121,150
Common Stock distributed pursuant to stock incentive plans (in shares)	2,395,210
Compensation for stock grants vesting in the future		3				3	19	22
Repurchase of common stock for employee tax withholding under stock incentive plans			(26)			(26)		(26)
Dividends paid to stockholders				(13)		(13)		(13)
Distributions from IBG LLC to noncontrolling interests							(165)	(165)
Adjustments for changes in proportionate ownership in IBG LLC		25				25	(25)
Comprehensive Income				60	3	63	467	530
Balance at Jun. 30, 2016	$ 1	$ 746	$ (29)	$ 192	$ 5	$ 915	$ 4,777	$ 5,692
Common stock, shares issued at Jun. 30, 2016	66,516,360

Organization And Nature Of Busi

Organization And Nature Of Business	6 Months Ended
	Jun. 30, 2016
Organization And Nature Of Business [Abstract]
Nature of Operations [Text Block]	1. Organization of Business Interactive Brokers Group, Inc. (“IBG, Inc.”) is a Delaware holding company whose primary asset is its ownership of approximately 16.2 % of the membership interests of IBG LLC, which, in turn, owns operating subsidiaries (collectively, “IBG LLC”). IBG, Inc. together with IBG LLC and its consolidated subsidiaries (collectively, “the Company”), is an automated global electronic broker and market maker specializing in executing and clearing trades in securities, futures, foreign exchange instruments, bonds and mutual funds on more than 100 electronic exchanges and market centers around the world and offering custody, prime brokerage, securities and margin lending services to customers. In the United States of America (“U.S.”), the Company conducts its business primarily from its headquarters in Greenwich, Connecticut and from Chicago, Illinois. Abroad, the Company conducts its business through offices located in Canada, England, Switzerland, Liechtenstein, India, China (Hong Kong and Shanghai), Japan, and Australia. As of June 30, 2016 , the Company had 1,169 employees worldwide. IBG LLC is a Connecticut limited liability company that conducts its business through its operating subsidiaries (collectively, the “Operating Companies”): Interactive Brokers LLC (“IB LLC”); Interactive Brokers Canada Inc. (“IBC”); Interactive Brokers (U.K.) Limited and its subsidiary, Interactive Brokers (U.K.) Nominee Limited (collectively, “IBUK”); Interactive Brokers Securities Japan, Inc. (“IBSJ”); Interactive Brokers Hong Kong Limited (“IBHK”); Interactive Brokers (India) Private Limited (“IBI”); Interactive Brokers Australia Pty Limited and its subsidiary, Interactive Brokers Australia Nominees Pty Limited (collectively, “IBA”); IB Business Services (Shanghai) Company Limited (“IBBSS”); Timber Hill LLC (“TH LLC”); Timber Hill Europe AG and its subsidiary, Timber Hill (Liechtenstein) AG (collectively, “THE”); Timber Hill Australia Pty Limited (“THA”); Timber Hill Canada Company (“THC”); Interactive Brokers Financial Products S.A. (“IBFP”); Interactive Brokers Hungary KFT (“IBH”); Interactive Brokers Software Services Estonia OU (“IBEST”); Interactive Brokers Software Services Russia (“IBRUS”); Interactive Brokers Software Services (India) Private Limited (“IBSSI”); and IB Exchange Corp. (“IBEC”) and its subsidiaries, Interactive Brokers Corp. (“IB Corp”), and Covestor, Inc. and its subsidiary, Covestor Limited (collectively, “Covestor”). The Company operates in two business segments: electronic brokerage and market making, both supported by corporate. The Company conducts its electronic brokerage business through certain Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide. The Company conducts its market making business principally through its Timber Hill subsidiaries on the world’s leading exchanges and market centers, primarily in exchange ‑traded equities, equity options and equity ‑index options and futures. Corporate enables the Company to operate cohesively and effectively by providing support via control functions to the business segments and also by executing the Company’s currency diversification strategy. Certain of the Operating Companies are members of various securities and commodities exchanges in North America, Europe and the Asia/Pacific region and are subject to regulatory capital and other requirements (see Note 13 ). IB LLC, IBC, IBUK, IBSJ, IBHK, and IBI carry securities accounts for customers or perform custodial functions relating to customer securities. 

Significant Accounting Policies

Significant Accounting Policies	6 Months Ended
	Jun. 30, 2016
Significant Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of Presentation These condensed consolidated financial statements are presented in U.S. dollars and have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10 ‑Q. These condensed consolidated financial statements are unaudited and should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s 2015 Annual Report on Form 10-K for the year ended December 31, 2015, which was filed with the SEC on February 29, 2016. The condensed consolidated financial information as of December 31, 2015 has been derived from the audited consolidated financial statements not included herein. These condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries and reflect all adjustments of a normal and recurring nature that are, in the opinion of management, necessary for the fair presentation of the results for the periods presented. The operating results for interim periods are not necessarily indicative of the operating results for the entire year. Principles of Consolidation, including Noncontrolling Interests  These condensed consolidated financial statements include the accounts of IBG, Inc. and its majority and wholly owned subsidiaries. As sole managing member of IBG LLC, IBG, Inc. exerts control over IBG LLC’s operations. In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, “ Consolidation, ” the Company consolidates IBG LLC’s financial statements and records the interests in IBG LLC that it does not own as noncontrolling interests. The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter ‑company balances and transactions have been eliminated. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in these condensed consolidated financial statements and accompanying notes. These estimates and assumptions are based on judgment and the best available information at the time. Therefore, actual results could differ materially from those estimates. Such estimates include the allowance for doubtful accounts, valuation of certain investments, compensation accruals, current and deferred income taxes, and contingency reserves. Fair Value Substantially all of the Company’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short ‑term in nature and are carried at amounts that approximate fair value. The Company applies the fair value hierarchy in accordance with FASB ASC Topic 820, “ Fair Value Measurement” (“ASC Topic 820”) , to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets and liabilities and the lowest priority to unobservable inputs. The three levels of the fair value hierarchy are:   Level 1 Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.  Level 2 Quoted prices in markets that are not considered to be active or financial instruments for which all significant inputs are observable, either directly or indirectly.  Level 3 Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.  Financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are generally classified as Level 1 of the fair value hierarchy. The Company’s Level 1 financial instruments, which are valued using quoted market prices as published by exchanges and clearing houses or otherwise broadly distributed in active markets, include active listed stocks, options, warrants and discount certificates, and U.S. and foreign government securities. The Company does not adjust quoted prices for financial instruments classified as Level 1 of the fair value hierarchy, even in the event that the Company may hold a large position whereby a purchase or sale could reasonably impact quoted prices. Currency forward contracts are valued using broadly distributed bank and broker prices, and are classified as Level 2 of the fair value hierarchy as such instruments are not exchange ‑traded. Other securities that are not traded in active markets are also classified in Level 2 of the fair value hierarchy. Level 3 financial instruments are comprised of securities that have been delisted or otherwise are no longer tradable and have been valued by the Company based on internal estimates. Earnings Per Share Earnings per share (“EPS”) is computed in accordance with FASB ASC Topic 260, “ Earnings per Share .” Basic EPS is computed by dividing the net income available for common stockholders by the weighted average number of shares outstanding for that period. Diluted EPS is calculated by dividing the net income available for common stockholders by the diluted weighted average shares outstanding for that period. Diluted EPS includes the determinants of the basic EPS and, in addition, reflects the dilutive effect of shares of common stock estimated to be distributed in the future under the Company’s stock-based compensation plans, with no adjustments to net income available for common stockholders for dilutive potential common shares. Stock ‑Based Compensation The Company follows FASB ASC Topic 718, “ Compensation - Stock Compensation” (“ASC Topic 718”) , to account for its stock ‑based compensation plans. ASC Topic 718 requires all share ‑based payments to employees to be recognized in the condensed consolidated financial statements using a fair value ‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows: 50% in the year of grant in recognition of plan forfeiture provisions (as described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC Topic 718. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted. Awards granted under stock ‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post ‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted. Cash and Cash Equivalents Cash and cash equivalents consist of deposits with banks and all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses. Cash and Securities - Segregated for Regulatory Purposes As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which have been promulgated to protect customer assets. Securities segregated for regulatory purposes consisted of U.S. government securities of $14.8 billion and $15.2 billion as of June 30, 2016 and December 31, 2015, respectively, and securities purchased under agreements to resell in the amount of $4.6 billion and $0.6 billion as of June 30, 2016 and December 31, 2015, respectively, which amounts approximate fair value. Securities Borrowed and Securities Loaned Securities borrowed and securities loaned are recorded at the amount of the cash collateral advanced or received. Securities borrowed transactions require the Company to provide counterparties with collateral, which may be in the form of cash, letters of credit or other securities. With respect to securities loaned, the Company receives collateral, which may be in the form of cash or other securities in an amount generally in excess of the fair value of the securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. It is the Company’s policy to net, in the condensed consolidated statements of financial condition, securities borrowed and securities loaned entered into with the same counterparty that meet the offsetting requirements prescribed in FASB ASC Topic 210-20, “Balance Sheet – Offsetting” (“ASC Topic 210-20”). Securities lending fees received and paid by the Company are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income. Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, the collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. It is the Company’s policy to net, in the condensed consolidated statements of financial condition, securities purchased under agreements to resell transactions and securities sold under agreements to repurchase transactions entered into with the same counterparty that meet the offsetting requirements prescribed in ASC Topic 210-20. Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased, at Fair Value Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold, but not yet purchased are stated at fair value based upon quoted market prices. The Company’s financial instruments pledged to counterparties where the counterparty has the right, by contract or custom, to sell or repledge the financial instruments are reported as financial instruments owned and pledged as collateral in the condensed consolidated statements of financial condition. The Company also enters into currency forward contracts. These transactions, which are also accounted for on a trade date basis, are agreements to exchange a fixed amount of one currency for a specified amount of a second currency at completion of the currency forward contract term. Unrealized mark ‑to ‑market gains and losses on currency forward contracts are included in financial instruments owned, at fair value or financial instruments sold, but not yet purchased, at fair value in the condensed consolidated statements of financial condition. Customer Receivables and Payables Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are recorded as customer bad debt expense in the condensed consolidated statements of comprehensive income. Receivables from and Payables to Brokers, Dealers and Clearing Organizations Receivables from and payables to brokers, dealers and clearing organizations include net receivables and payables from unsettled trades, including amounts related to futures and options on futures contracts executed on behalf of customers, amounts receivable for securities not delivered by the Company to the purchaser by the settlement date (“fails to deliver”) and cash deposits. Payables to brokers, dealers and clearing organizations also include amounts payable for securities not received by the Company from a seller by the settlement date (“fails to receive”). Investments The Company makes certain strategic investments related to its business and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under FASB ASC Topic 323, “ Investments - Equity Method and Joint Ventures .” Investments accounted for under the equity method, including where the investee is a limited partnership or limited liability company, are recorded at the fair value amount of the Company’s initial investment and are adjusted each period for the Company’s share of the investee’s income or loss. The Company’s share of the income or losses from equity method investments is included in other income in the condensed consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $21 million as of June 30, 2016 ( $ 3 2 million as of December 31, 2015), which are included in other assets in the condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity method investees are recorded as additions or reductions, respectively, to the respective investment balance. The Company also holds exchange memberships and investments in equity securities of certain exchanges, as required to qualify as a clearing member, and strategic investments in corporate stock that do not qualify for equity method accounting. Such investments, $34 million as of June 30, 2016 ($ 34 million as of December 31, 2015), are recorded at cost or, if an other ‑than ‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also included in other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the condensed consolidated statements of comprehensive income when such dividends are received. A judgmental aspect of accounting for investments is evaluating whether an other ‑than ‑temporary decline in the value of an investment has occurred. The evaluation of an other ‑than ‑temporary impairment is dependent on specific quantitative and qualitative factors and circumstances surrounding an investment, including recurring operating losses, credit defaults and subsequent rounds of financing. The Company’s equity investments do not have readily determinable market values. All investments are reviewed for changes in circumstances or occurrence of events that suggest the Company’s investment may not be recoverable. If an unrealized loss on any investment is considered to be other ‑than ‑temporary, the loss is recognized in the period the determination is made . Property, Equipment and Intangible Assets Property, equipment and intangible assets, which are included in other assets in the condensed consolidated statements of financial condition, consist of leasehold improvements, computer equipment, software developed for the Company’s internal use, office furniture, equipment and acquired technology . Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Additions and improvements that extend the lives of assets are capitalized, while expenditures for repairs and maintenance are expensed as incurred. Depreciation and amortization are computed using the straight ‑line method. Equipment is depreciated over the estimated useful lives of the assets, while leasehold improvements are amortized over the lesser of the estimated economic useful life of the asset or the term of the lease. Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years Intangible assets with a finite life are amortized on a straight line basis over their estimated useful lives of three years, and tested for recoverability whenever events indicate that the carrying amounts may not be recoverable. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years. Comprehensive Income and Foreign Currency Translation The Company’s operating results are reported in the condensed consolidated statements of comprehensive income pursuant to FASB ASC Topic 220, “ Comprehensive Income. ” Comprehensive income consists of two components: net income and other comprehensive income (“OCI”). The Company’s OCI is comprised of gains and losses resulting from translating foreign currency financial statements of non-U.S. subsidiaries , net of related income taxes, where applicable. In general, the practice and intention of the Company is to reinvest the earnings of its non ‑U.S. subsidiaries in those operations, therefore tax is usually not accrued. The Company’s non ‑U.S. domiciled subsidiaries have a functional currency that is other than the U.S. dollar. Such subsidiaries’ assets and liabilities are translated into U.S. dollars at period ‑end exchange rates, and revenues and expenses are translated at average exchange rates prevailing during the period. Adjustments that result from translating amounts from a subsidiary’s functional currency to the U.S. dollar (as described above) are reported net of tax, where applicable, in accumulated OCI in the condensed consolidated statements of financial condition. Revenue Recognition Trading Gains Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains and losses are comprised of changes in the fair value of financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value (i.e., unrealized gains and losses) and realized gains and losses related to the Company’s market making business segment. Included in trading gains are net gains and losses on stocks, U.S. and foreign government securities, options, futures, foreign exchange and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are reported on a net basis in trading gains in the condensed consolidated statements of comprehensive income. Commissions and Execution Fees Commissions earned for executing and clearing transactions are accrued on a trade date basis and are reported as commissions and execution fees in the condensed consolidated statements of comprehensive income. Interest Income and Expense The Company earns interest income and incurs interest expense primarily in connection with its electronic brokerage customer business and its securities lending activities, which are recorded on an accrual basis and are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income. Foreign Currency Gains and Losses Currency translation refers to the gains and losses resulting from foreign currency transactions. Foreign currency translation gains and losses related to the Company’s currency diversification strategy are included in other income in the condensed consolidated statements of comprehensive income. Foreign currency translation gains and losses related to the market making core-business activities are included in trading gains in the condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency translation gains and losses, arising from currency swap transactions, are included in interest income in the condensed consolidated statements of comprehensive income R ebates Rebates consist of volume discounts, credits or payments received from exchanges or other market centers related to the placement and/or removal of liquidity from the order flow in the marketplace. Rebates are recorded on an accrual basis and included net within execution and clearing expenses in the condensed consolidated statements of comprehensive income. Rebates received for trades executed on behalf of customers that elect tiered pricing are passed, in whole or part, to these customers; and such pass-through amounts are recorded net within commissions and execution fees in the condensed consolidated statements of comprehensive income.  Income Taxes The Company accounts for income taxes in accordance with FASB ASC Topic 740, “ Income Taxes” (“ASC Topic 740”) . The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (see Note 10) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates. The Company recognizes interest related to income tax matters as interest income or interest expense and penalties related to income tax matters as income tax expense in the condensed consolidated statements of comprehensive income. Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of the underlying assets and liabilities. In evaluating the ability to recover deferred tax assets within the jurisdictions from which they arise, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax ‑planning strategies, and results of recent operations. In projecting future taxable income, historical results are adjusted for changes in accounting policies and incorporate assumptions including the amount of future state, federal and foreign pre-tax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax ‑planning strategies. These assumptions require significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates the Company is using to manage the underlying businesses. In evaluating the objective evidence that historical results provide, three years of cumulative operating income (loss) are considered. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on the unremitted earnings of foreign subsidiaries that have been indefinitely reinvested. The calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax laws and regulations in a multitude of jurisdictions across the Company’s global operations. Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position. The Company recognizes that a tax benefit from an uncertain tax position only when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, on the basis of the technical merits. A tax position that meets this standard is measured at the largest amount of benefit that will more likely than not be realized on settlement. The Company records tax liabilities in accordance with ASC Topic 740 and adjusts these liabilities when management’s judgment changes as a result of the evaluation of new information not previously available. Because of the complexity of some of these uncertainties, the ultimate resolution may result in payments that are different from the current estimates of these tax liabilities. These differences will be reflected as increases or decreases to income tax expense in the period in which new information becomes available. Recently Issued Accounting Pronouncements Following is a summary of recently issued FASB Accounting Standards Updates (“ASUs”) that have affected or may affect the Company’s condensed consolidated financial statements :    Affects Status   ASU 2014-15 Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. Effective for the annual period ending after December 15, 2016.   ASU 2015-14 Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-01 Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. Effective for fiscal years beginning after December 15, 2017.   ASU 2016-02 Leases (Topic 842) : Requires that, at lease inception, a lessee recognize a right-of-use asset, representing the right to use the underlying asset for the lease term, and a lease liability, representing the liability to make lease payments, in the statements of financial condition, among other requirements. Effective for fiscal years beginning after December 15, 2018.   ASU 2016-07 Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting. Effective beginning after December 15, 2016.   ASU 2016-08 Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net). Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-09 Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. Effective for annual reporting periods beginning after December 15, 2016.   ASU 2016-10 Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-12 Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Effective for fiscal years beginning after December 15, 2019.   Adoption of those ASUs that became effective during 2015 and 2016, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on these financial statements. The Company early adopted ASU 2016-09 Compensation – Stock Compensation (Topic 718), Improvements to Employee Share-Based Payment Accounting, as of April 1, 2016. This early adoption did not have a material impact on the Company’s condensed consolidated financial statements.

Trading Activities And Related

Trading Activities And Related Risks	6 Months Ended
	Jun. 30, 2016
Trading Activities And Related Risks [Abstract]
Trading Activities And Related Risks	3. Trading Activities and Related Risks The Company’s trading activities include providing securities market making and brokerage services. Trading activities expose the Company to market and credit risks. These risks are managed in accordance with established risk management policies and procedures. To accomplish this, management has established a risk management process that includes: • a regular review of the risk management process by executive management as part of its oversight role; • defined risk management policies and procedures supported by a rigorous analytic framework; and • articulated risk tolerance levels as defined by executive management that are regularly reviewed to ensure that the Company’s risk ‑taking is consistent with its business strategy, capital structure, and current and anticipated market conditions. Market Risk The Company is exposed to various market risks. Exposures to market risks arise from equity price risk, foreign currency exchange rate fluctuations and changes in interest rates. The Company seeks to mitigate market risk associated with trading inventories by employing hedging strategies that correlate rate, price and spread movements of trading inventories and related financing and hedging activities. The Company uses a combination of cash instruments and exchange traded derivatives to hedge its market exposures. The Company does not apply hedge accounting. The following discussion describes the types of market risk faced: Equity Price Risk Equity price risk arises from the possibility that equity security prices will fluctuate, affecting the value of equity securities and other instruments that derive their value from a particular stock, a defined basket of stocks, or a stock index. The Company is subject to equity price risk primarily in financial instruments. The Company attempts to limit such risks by continuously reevaluating prices and by diversifying its portfolio across many different options, futures and underlying securities and avoiding concentrations of positions based on the same underlying security. Currency Risk Currency risk arises from the possibility that fluctuations in foreign exchange rates will impact the value of financial instruments. The Company manages this risk using spot (i.e., cash) currency transactions, currency futures contracts and currency forward contracts. As a global electronic broker and market maker trading on exchanges around the world in multiple currencies, the Company is exposed to foreign currency risk. The Company actively manages its currency exposure using hedging strategies that are based on a defined basket of 16 currencies internally referred to as the “GLOBAL.” These strategies minimize the fluctuation of the Company’s net worth as expressed in GLOBALs, thereby diversifying its risk in alignment with these global currencies, weighted by the Company’s view of their importance. As the Company’s financial results are reported in U.S. dollars, the change in the value of the GLOBAL as expressed in U.S. dollars affects the Company’s earnings. The impact of this currency diversification strategy in the Company’s earnings is included in other income in the condensed consolidated statements of comprehensive income. As a result of a periodic assessment, the Company changed the composition of the GLOBAL by adding the Chinese renminbi (specifically, the offshore currency known by the symbol CNH), removing the South Korean won (KRW) and Brazilian real (BRL) components, and realigning the relative weights of the U.S. dollar (USD) and Japanese yen (JPY). The new composition of the GLOBAL went into effect as of the close of business on June 30, 2016 ; hence, this change had no impact on the results for the second quarter of 2016 . Interest Rate Risk Interest rate risk arises from the possibility that changes in interest rates will affect the value of financial instruments. The Company is exposed to interest rate risk on cash and margin balances, positions carried in equity and fixed income securities, options, and futures and on its borrowings. These risks are managed through investment policies and by entering into interest rate futures contracts. Credit Risk The Company is exposed to risk of loss if an individual, counterparty or issuer fails to perform its obligations under contractual terms (“default risk”). Both cash instruments and derivatives expose the Company to default risk. The Company has established policies and procedures for mitigating credit risk on principal transactions, including reviewing and establishing limits for credit exposure, maintaining collateral, and continually assessing the creditworthiness of counterparties. The Company’s credit risk is limited in that substantially all of the contracts entered into are settled directly at securities and commodities clearing houses and a small portion is settled through member firms and banks with substantial financial and operational resources. The Company seeks to control the risks associated with its customer margin activities by requiring customers to maintain collateral in compliance with regulatory and internal guidelines. In the normal course of business, the Company executes, settles, and finances various customer securities transactions. Execution of these transactions includes the purchase and sale of securities which exposes the Company to default risk arising from the potential that customers or counterparties may fail to satisfy their obligations. In these situations, the Company may be required to purchase or sell financial instruments at unfavorable market prices to satisfy obligations to customers or counterparties. Liabilities to other brokers and dealers related to unsettled transactions (i.e., securities fails to receive) are recorded at the amount for which the securities were purchased, and are paid upon receipt of the securities from other brokers or dealers. In the case of aged securities fails to receive, the Company may purchase the underlying security in the market and seek reimbursement for any losses from the counterparty. For cash management purposes, the Company enters into short ‑term securities purchased under agreements to resell and securities sold under agreements to repurchase transactions (“repos”) in addition to securities borrowing and lending arrangements, all of which may result in credit exposure in the event the counterparty to a transaction is unable to fulfill its contractual obligations. Repos are collateralized by securities with a market value in excess of the obligation under the contract. Similarly, securities lending agreements are collateralized by deposits of cash or securities. The Company attempts to minimize credit risk associated with these activities by monitoring collateral values on a daily basis and requiring additional collateral to be deposited with or returned to the Company as permitted under contractual provisions. Concentrations of Credit Risk The Company’s exposure to credit risk associated with its trading and other activities is measured on an individual counterparty basis, as well as by groups of counterparties that share similar attributes. Concentrations of credit risk can be affected by changes in political, industry, or economic factors. To reduce the potential for risk concentration, credit limits are established and exposure is monitored in light of changing counterparty and market conditions. As of June 30, 2016, the Company did not have any material concentrations of credit risk outside the ordinary course of business. Off ‑Balance Sheet Risks The Company may be exposed to a risk of loss not reflected in the condensed consolidated financial statements to settle futures and certain over ‑the ‑counter contracts at contracted prices, which may require repurchase or sale of the underlying products in the market at prevailing prices. Accordingly, these transactions result in off ‑balance sheet risk as the Company’s cost to liquidate such contracts may exceed the amounts reported in the Company’s condensed consolidated statements of financial condition.  

Equity And Earnings Per Share

Equity And Earnings Per Share	6 Months Ended
	Jun. 30, 2016
Equity And Earnings Per Share [Abstract]
Equity And Earnings Per Share	4. Equity and Earnings Per Share In connection with IBG, Inc.’s initial public offering of Class A common stock (“IPO”) in May 2007, it purchased 10.0% of the membership interests in IBG LLC from IBG Holdings LLC (“Holdings”), became the sole managing member of IBG LLC and began to consolidate IBG LLC’s financial results into its financial statements. Holdings owns all of IBG, Inc.’s Class B common stock, which has voting rights in proportion to its ownership interests in IBG LLC . The table below shows the amount of IBG LLC membership interests held by IBG, Inc. and Holdings as of June 30, 2016.     IBG, Inc. Holdings Total  Ownership % 16.2% 83.8% 100.0%  Membership interests 66,386,915 343,040,504 409,427,419  These condensed consolidated financial statements reflect the results of operations and financial position of IBG, Inc., including consolidation of its investment in IBG LLC and its subsidiaries. The noncontrolling interests in IBG LLC attributable to Holdings are reported as a component of total equity in the condensed consolidated statements of financial condition. Recapitalization and Post ‑IPO Capital Structure Immediately prior to and immediately following the consummation of the IPO, IBG, Inc., Holdings, IBG LLC and the members of IBG LLC consummated a series of transactions collectively referred to herein as the “Recapitalization.” In connection with the Recapitalization, IBG, Inc., Holdings and the historical members of IBG LLC entered into an exchange agreement, dated as of May 3, 2007 (the “Exchange Agreement”), pursuant to which the historical members of IBG LLC received membership interests in Holdings in exchange for their membership interests in IBG LLC. Additionally, IBG, Inc. became the sole managing member of IBG LLC. In connection with the consummation of the IPO, Holdings used the net proceeds to redeem 10.0% of members’ interests in Holdings in proportion to their interests. Immediately following the Recapitalization and IPO, Holdings owned approximately 90% of IBG LLC and 100% of IBG, Inc.’s Class B common stock, which has voting power in IBG, Inc. in proportion to Holdings’ ownership of IBG LLC. Since consummation of the IPO and Recapitalization, IBG, Inc.’s equity capital structure has been comprised of Class A and Class B common stock. All shares of common stock have a par value of $0.01 per share and have identical rights to earnings and dividends and in liquidation. As of June 30, 2016 and December 31, 2015 , 1,000,000,000 shares of Class A common stock were authorized, of which 66,516,360 and 64,121,150 shares have been issued; and 65,671,645 and 63,985,335 shares were outstanding, respectively. Class B common stock is comprised of 100 authorized shares, of which 100 shares were issued and outstanding as of June 30, 2016 and December 31, 2015 , respectively. In addition, 10,000 shares of preferred stock have been authorized, of which no shares are issued or outstanding as of June 30, 2016 and December 31, 2015 , respectively. As a result of a federal income tax election made by IBG LLC applicable to the acquisition of IBG LLC member interests by IBG, Inc., the income tax basis of the assets of IBG LLC acquired by IBG, Inc. have been adjusted based on the amount paid for such interests. Deferred tax assets were recorded as of the IPO date and in connection with subsequent redemptions of Holdings member interests in exchange for common stock. These deferred tax assets are included in other assets in the Company’s condensed consolidated statements of financial condition and are being amortized as additional deferred income tax expense over 15 years from the IPO date and from the additional redemption dates, respectively, as allowable under current tax law. As of June 30, 2016 and December 31, 2015 , the unamortized balance of these deferred tax assets was $275 million and $288 million, respectively. IBG, Inc. also entered into an agreement (the “Tax Receivable Agreement”) with Holdings to pay Holdings (for the benefit of the former members of IBG LLC) 85% of the tax savings that IBG, Inc. actually realizes as the result of tax basis increases. These payables to Holdings are reported as payable to affiliate in the Company’s condensed consolidated statements of financial condition. The remaining 15% is accounted for as a permanent increase to additional paid ‑in capital in the Company’s condensed consolidated statements of financial condition. The cumulative amounts of deferred tax assets, payables to Holdings and additional paid ‑in capital arising from stock offerings from the date of the IPO through June 30, 2016 were $460 million, $391 million and $69 million, respectively. Amounts payable under the Tax Receivable Agreement are payable to Holdings annually following the filing of IBG, Inc.’s federal income tax return. The Company has paid Holdings a cumulative total of $116 million through June 30, 2016 pursuant to the terms of the Tax Receivable Agreement. The Exchange Agreement, as amended, provides for future redemptions of member interests and for the purchase of member interests in IBG LLC by IBG, Inc. from Holdings, which could result in IBG, Inc. acquiring the remaining member interests in IBG LLC that it does not own. On an annual basis, members of Holdings are able to request redemption of their interests. At the time of IBG, Inc.’s IPO in 2007, three hundred sixty (360) million shares of authorized common stock were reserved for future sales and redemptions. From 2008 through 2010, Holdings redeemed 5,013,259 IBG LLC interests with a total value of $114 million, which redemptions were funded using cash on hand at IBG LLC. Upon cash redemption these IBG LLC interests were retired. From 2011 through 2015, IBG, Inc. issued 11,047,295 shares of common stock (with a fair value of $306 million) directly to Holdings in exchange for an equivalent number of member interests in IBG LLC . As a consequence of these redemption transactions, and distribution of shares to employees (see Note 9 ), IBG, Inc. ’ s interest in IBG LLC has increased to approximately 16.2% , with Holdings owning the remaining 83.8% as of June 30, 2016 . The redemptions also resulted in an increase in the Holdings interest held by Mr. Thomas Peterffy and his affiliates from approximately 84.6% at the IPO to approximately 88.7% as of June 30, 2016 .  On July 28, 2016, the Company filed a Supplemental Prospectus on Form 424B5 (File Number 333-192275) with the SEC to issue 1,596,200 shares of common stock in exchange for an equivalent number of shares of member interests in IBG LLC. This issuance of shares increased the Company’s ownership in IBG LLC from 16.2% to 16.6% . Earnings per Share  Basic earnings per share is calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period.    Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)  Basic earnings per share  Net income available for common stockholders $ 27 $ 23 $ 60 $ 10  Weighted average shares of common stock outstanding  Class A 64,967,264 59,481,678 64,476,321 58,980,248  Class B 100 100 100 100  64,967,364 59,481,778 64,476,421 58,980,348  Basic earnings per share $ 0.41 $ 0.38 $ 0.93 $ 0.17  Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares.     Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)  Diluted earnings per share  Net income available for common stockholders $ 27 $ 23 $ 60 $ 10  Weighted average shares of common stock outstanding  Class A  Issued and outstanding 64,967,264 59,481,678 64,476,321 58,980,248  Potentially dilutive common shares  Issuable pursuant to employee stock incentive plans 1,503,549 1,557,148 1,386,987 1,456,566  Class B 100 100 100 100  66,470,913 61,038,926 65,863,408 60,436,914  Diluted earnings per share $ 0.40 $ 0.37 $ 0.91 $ 0.17  Member Distributions and Stockholder Dividends During the six months ended June 30, 2016 , IBG LLC made distributions totaling $197 million, to its members, of which IBG, Inc. ’ s proportionate share was $32 million. For the six months ended June 30, 2016, t he Company paid cash dividends of $0.10 per share of c ommon s tock, totaling $13 million . On July 19, 2016 , the Company declared a cash dividend of $0.10 per common share, payable on September 14, 2016 to stockholders of record as of September 1, 2016 .

Comprehensive Income

Comprehensive Income	6 Months Ended
	Jun. 30, 2016
Comprehensive Income Detail [Abstract]
Comprehensive Income	5. Comprehensive Income The following table presents comprehensive income and earnings per share on comprehensive income.      Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)   Comprehensive income available for common stockholders $ 24 $ 27 $ 63 $ 13   Earnings per share on comprehensive income  Basic $ 0.36 $ 0.45 $ 0.97 $ 0.22  Diluted $ 0.36 $ 0.44 $ 0.95 $ 0.21  Weighted average common shares outstanding  Basic 64,967,364 59,481,778 64,476,421 58,980,348  Diluted 66,470,913 61,038,926 65,863,408 60,436,914    

Financial Assets And Financial

Financial Assets And Financial Liabilities	6 Months Ended
	Jun. 30, 2016
Financial Assets And Financial Liabilities [Abstract]
Financial Assets And Financial Liabilities	6. Financial Assets and Financial Liabilities Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis The following tables set forth, by level within the fair value hierarchy (see Note 2), financial assets and liabilities, measured at fair value on a recurring basis as of June 30, 2016 and December 31, 2015 . As required by ASC Topic 820, financial assets and financial liabilities are classified in their entirety based on the lowest level of input that is significant to the respective fair value measurement.     Financial Assets At Fair Value as of June 30, 2016   Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 14,753 $ — $ — $ 14,753  Financial instruments owned  Stocks 1,943 — — 1,943  Options 1,742 — — 1,742  Warrants and discount certificates 52 — — 52  U.S. and foreign government securities 490 — — 490  Corporate and municipal bonds — 3 — 3  Currency forward contracts — 24 — 24  Total financial instruments owned, at fair value 4,227 27 — 4,254  Total financial assets at fair value $ 18,980 $ 27 $ — $ 19,007      Financial Liabilities At Fair Value as of June 30, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 1,567 $ — $ — $ 1,567  Options 1,296 — — 1,296  Warrants and discount certificates 2 — — 2  Currency forward contracts — 9 — 9  Total financial instruments sold, but not yet purchased, at fair value 2,865 9 — 2,874  Total financial liabilities at fair value $ 2,865 $ 9 $ — $ 2,874        Financial Assets At Fair Value as of December 31, 2015  Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 15,214 $ — $ — $ 15,214  Financial instruments owned, at fair value  Stocks 1,650 — — 1,650  Options 1,156 — — 1,156  Warrants and discount certificates 81 — — 81  U.S. and foreign government securities 527 — — 527  Corporate and municipal bonds — 3 — 3  Currency forward contracts — 3 — 3  Total financial instruments owned, at fair value 3,414 6 — 3,420  Total financial assets at fair value $ 18,628 $ 6 $ — $ 18,634        Financial Liabilities At Fair Value as of December 31, 2015  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 1,565 $ — $ — $ 1,565  Options 1,042 — — 1,042  Warrants and discount certificates 1 — — 1  Currency forward contracts — 9 — 9  Total financial instruments sold, but not yet purchased, at fair value 2,608 9 — 2,617  Total financial liabilities at fair value $ 2,608 $ 9 $ — $ 2,617 Transfers between Level 1 and Level 2 Transfers of financial assets and financial liabilities at fair value to or from Levels 1 and 2 arise where the market for a specific financial instrument has become active or inactive during the period. The fair values transferred are ascribed as if the financial assets or financial liabilities had been transferred as of the end of the period. During the six months ended June 30, 2016 and 2015 , there were no transfers between levels for financial assets and liabilities, at fair value. Trading Gains from Market Making Transactions Trading gains and losses from market making transactions reported in the statements of comprehensive income, by major product type, are comprised of :     Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Equities $ 35 $ 70 $ 85 $ 121  Fixed income — — — —  Foreign exchange (1) (3) 1 8  Total trading gains, net $ 34 $ 67 $ 86 $ 129  These transactions are related to the Company’s financial instruments owned and financial instruments sold, but not yet purchased, at fair value and include both derivative and non ‑derivative financial instruments, including exchange traded options and futures. These gains and losses also include market making related dividend and fixed income trading related interest income and expense. The gains in the table above are not representative of the integrated trading strategies applied by the Company, which utilizes financial instruments across various product types. Gains and losses in one product type frequently offset gains and losses in other product types. Financial Assets and Liabilities Not Measured at Fair Value The following table represents the carrying value, fair value, and fair value hierarchy category of certain financial assets and liabilities that are not recorded at fair value in the Company's condensed consolidated statements of financial condition. The following table excludes certain financial instruments such as equity investments and all non-financial assets and liabilities.      June 30, 2016  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,443 $ 1,443 $ 1,443 $ - $ -  Cash and securities segregated for regulatory purposes 10,504 10,504 5,891 4,613 -  Securities borrowed 3,760 3,760 - 3,760 -  Securities purchased under agreements to resell 113 113 - 113 -  Receivables from customer 15,137 15,137 - 15,137 -  Receivables from broker, dealers, and clearing organizations 1,351 1,351 - 1,351 -  Interest receivable 58 58 - 58 -  Other assets 29 31 - 31 -  Total financial assets, not measured at fair value $ 32,395 $ 32,397 $ 7,334 $ 25,063 $ —       Financial liabilities, not measured at fair value  Short-term borrowings $ 8 $ 8 $ - $ 8 $ -  Securities loaned 3,270 3,270 - 3,270 -  Payables to customer 39,319 39,319 - 39,319 -  Payables to brokers, dealers and clearing organizations 286 286 - 286 -  Interest payable 4 4 - 4 -  Total financial liabilities, not measured at fair value $ 42,887 $ 42,887 $ - $ 42,887 $ -       December 31, 2015  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,601 $ 1,601 $ 1,601 $ - $ -  Cash and securities segregated for regulatory purposes 6,095 6,095 5,533 562 -  Securities borrowed 3,924 3,924 - 3,924 -  Securities purchased under agreements to resell 195 195 - 195 -  Receivables from customer 17,050 17,050 - 17,050  Receivables from broker, dealers, and clearing organizations 692 692 - 692 -  Interest receivable 63 63 - 63 -  Other assets 28 31 - 31 -  Total financial assets, not measured at fair value $ 29,648 $ 29,651 $ 7,134 $ 22,517 $ —         Financial liabilities, not measured at fair value  Securities loaned $ 2,894 $ 2,894 $ - $ 2,894 $ -  Payables to customer 37,084 37,084 - 37,084 -  Payables to brokers, dealers and clearing organizations 423 423 - 423 -  Interest payable 3 3 - 3 -  Total financial liabilities, not measured at fair value $ 40,404 $ 40,404 $ — $ 40,404 $ —   Netting of Financial Assets and Financial Liabilities  It is the Company’s policy to net securities borrowed and securities loaned, and securities purchased under agreements to resell and securities sold under agreements to repurchase that meet the offsetting requirements prescribed in ASC Topic 210-20. In the tables below, the amounts of financial instruments that are not offset in the condensed consolidated statements of financial condition, but could be netted against cash or financial instruments with specific counterparties under master netting agreements, according to the terms of the agreements, including clearing houses (exchange traded options, warrants and discount certificates) or over the counter currency forward contract counterparties, are presented to provide financial statement readers with the Company’s net payable or receivable with counterparties for these financial instruments.  The following tables sets forth the netting of financial assets and of financial liabilities as of June 30, 2016 and December 31, 2015 .     June 30, 2016  Gross Amounts Net Amounts Amounts Not Offset  Amounts Offset in the Presented in in the Condensed  of Financial Condensed Condensed Consolidated Statement  Assets and Consolidated Consolidated of Financial Condition  Liabilities Statement of Statement of Cash or Financial  Recognized Financial Condition 2 Financial Condition Instruments Net Amount   (in millions)  Offsetting of Financial Assets  Securities segregated for regulatory purposes - purchased under agreements to resell $ 4,613 1 $ — $ 4,613 $ (4,613) $ —  Securities borrowed 3,760 — 3,760 (3,644) 116  Securities purchased under agreements to resell 113 — 113 (113) —  Financial Instruments owned, at fair value  Options 1,742 — 1,742 (1,219) 523  Warrants and discount certificates 52 — 52 (2) 50  Currency forward contracts 24 — 24 — 24  Total $ 10,304 $ — $ 10,304 $ (9,591) $ 713     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 3,270 $ — $ 3,270 $ (3,168) $ 102  Financial instruments sold, but not yet purchased, at fair value  Options 1,296 — 1,296 (1,219) 77  Warrants and discount certificates 2 — 2 (2) —  Currency forward contracts 9 — 9 — 9  Total $ 4,577 $ — $ 4,577 $ (4,389) $ 188       December 31, 2015  Gross Amounts Net Amounts Amounts Not Offset  Amounts Offset in the Presented in in the Condensed  of Financial Condensed Condensed Consolidated Statement  Assets and Consolidated Consolidated of Financial Condition  Liabilities Statement of Statement of Cash or Financial  Recognized Financial Condition 2 Financial Condition Instruments Net Amount   (in millions)  Offsetting of Financial Assets  Securities segregated for regulatory purposes - purchased under agreements to resell $ 562 1 $ — $ 562 $ (562) $ —  Securities borrowed 3,924 — 3,924 (3,816) 108  Securities purchased under agreements to resell 195 — 195 (195) —  Financial Instruments owned, at fair value  Options 1,156 — 1,156 (1,032) 124  Warrants and discount certificates 81 — 81 (1) 80  Currency forward contracts 3 — 3 — 3  Total $ 5,921 $ — $ 5,921 $ (5,606) $ 315     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 2,894 $ — $ 2,894 $ (2,773) $ 121  Financial instruments sold, but not yet purchased, at fair value  Options 1,042 — 1,042 (1,032) 10  Warrants and discount certificates 1 — 1 (1) —  Currency forward contracts 9 — 9 — 9  Total $ 3,946 $ — $ 3,946 $ (3,806) $ 140   (1) As of June 30, 2016 and December 31, 2015, the Company had $4.6 billion and $0.6 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities - segregated for regulatory purposes” in the condensed consolidated statements of financial condition. (2) The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at June 30, 2016 and December 31, 2015.  Secured Financing Transactions – Maturities and Collateral Pledged  The following table presents gross obligations for securities loaned transactions by remaining contractual maturity and class of collateral pledged.      June 30, 2016  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 3,248 $ - $ - $ - $ 3,248  Corporate bonds 22 - - - 22  Total $ 3,270 $ - $ - $ - $ 3,270       December 31, 2015  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 2,873 $ - $ - $ - $ 2,873  Corporate bonds 21 - - - 21  Total $ 2,894 $ - $ - $ - $ 2,894  

Collateralized Transactions

Collateralized Transactions	6 Months Ended
	Jun. 30, 2016
Disclosure Collateralized Transactions [Abstract]
Collateralized Transactions	 7. Collateralized Transactions The Company enters into securities borrowing and lending transactions and agreements to repurchase and resell securities to finance trading inventory, to obtain securities for settlement and to earn residual interest rate spreads. In addition, the Company’s customers pledge their securities owned to collateralize margin loans. Under these transactions, the Company either receives or provides collateral, including equity, corporate debt and U.S. government securities. Under many agreements, the Company is permitted to sell or repledge securities received as collateral and use these securities to secure securities purchased under agreements to resell, enter into securities lending transactions or deliver these securities to counterparties to cover short positions. The Company also engages in securities financing transactions with and for customers through margin lending. Customer receivables generated from margin lending activity are collateralized by customer ‑owned securities held by the Company. Customers’ required margin levels and established credit limits are monitored continuously by risk management staff using automated systems. Pursuant to the Company’s policy and as enforced by such systems, customers are required to deposit additional collateral or reduce positions, when necessary to avoid automatic liquidation of their positions. Margin loans are extended to customers on a demand basis and are not committed facilities. Factors considered in the acceptance or rejection of margin loans are the amount of the loan, the degree of leverage being employed in the customer account and an overall evaluation of the customer’s portfolio to ensure proper diversification or, in the case of concentrated positions, appropriate liquidity of the underlying collateral. Additionally, transactions relating to concentrated or restricted positions are limited or prohibited by raising the level of required margin collateral (to 100% in the extreme case). Underlying collateral for margin loans is evaluated with respect to the liquidity of the collateral positions, valuation of securities, volatility analysis and an evaluation of industry concentrations. Adherence to the Company’s collateral policies significantly limits the Company’s credit exposure to margin loans in the event of a customer’s default. Under margin lending agreements, the Company may request additional margin collateral from customers and may sell securities that have not been paid for or purchase securities sold but not delivered from customers, if necessary. As of June 30, 2016 and December 31, 2015 , approximately $15.1 billion and $17.0 billion, respectively, of customer margin loans were outstanding. The following table summarizes the amounts related to collateralized transactions as of June 30, 2016 and December 31, 2015 :     June 30, 2016 December 31, 2015  Permitted Sold or Permitted Sold or  to Repledge Repledged to Repledge Repledged   (in millions)  Securities lending transactions $ 11,809 $ 3,743 $ 12,131 $ 2,229  Securities purchased under agreements to resell transactions (1) 4,724 4,724 757 743  Customer margin assets 13,806 6,989 14,905 6,279  $ 30,339 $ 15,456 $ 27,793 $ 9,251  (1) As of June 30, 2016 , $4.6 billion or 98% ( 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 customer s in accordance with SEC Rule 15c3-3. In the normal course of business, the Company pledges qualified securities with clearing organizations to satisfy daily margin and clearing fund requirements. As of June 30, 2016 and December 31, 2015, the majority of the Company’s U.S. and foreign government securities owned were pledged to clearing organizations. Financial instruments owned and pledged as collateral, including amounts pledged to affiliates, where the counterparty has the right to repledge, as of June 30, 2016 and December 31, 2015 are presented in the following table :     June 30, December 31,  2016 2015   (in millions)  Stocks $ 1,186 $ 915  U.S. and foreign government securities 488 518  $ 1,674 $ 1,433  

Other Income

Other Income	6 Months Ended
	Jun. 30, 2016
Other Income [Abstract]
Other Income	8 . Other Income The components of other income for the three months and six months ended June 30, 2016 and 2015 were:     Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Payments for order flow $ 3 $ 4 $ 7 $ 8  Market data fees 8 6 17 13  Account activity fees 5 4 9 8  Risk exposure fees 4 7 9 11  Gains on financial instruments, at fair value and other investments, net 16 3 51 35  Gains (losses) from currency diversification strategy, net 17 25 101 (162)  Other, net 4 6 7 10  $ 57 $ 55 $ 201 $ (77)  Payments for order flow are earned from various options exchanges based upon options trading volume originated by the Operating Companies. Market data fees are charged to customers based upon market data services provided and are largely offset by the related cost to obtain the underlying market data from third party vendors. Risk exposure fees are earned from a small minority of customers’ accounts with positions on which market risk exceeds certain thresholds . Gains and losses on financial instruments, at fair value and other investments include realized and unrealized gains and losses on financial instruments that are not held for the Company’s market making operations or from securities that are subject to restrictions, and the Company’s interests in the earnings of equity method investees and dividends received on cost ‑basis investments. 

Employee Incentive Plans

Employee Incentive Plans	6 Months Ended
	Jun. 30, 2016
Employee Incentive Plans [Abstract]
Employee Incentive Plans	9 . Employee Incentive Plans Defined Contribution Plan The Company offers substantially all employees of U.S.-based Operating Companies who have met minimum service requirements the opportunity to participate in defined contribution retirement plans qualifying under the provisions of Section 401(k) of the Internal Revenue Code. The general purpose of this plan is to provide employees with an incentive to make regular savings in order to provide additional financial security during retirement. This plan provides for the Company to match 50% of the employees’ pre-tax contribution, up to a maximum of 10% of eligible earnings. The employee is vested in the matching contribution incrementally over six years. Included in employee compensation and benefits expenses in the condensed consolidated statements of comprehensive income were $2 million and $1 million of plan contributions for the six months ended June 30, 2016 and 2015 , respectively. 2007 ROI Unit Stock Plan In connection with the IPO, the Company adopted the IBG , Inc. 2007 ROI Unit Stock Plan (“ ROI Unit Stock Plan”). An aggregate of 1,271,009 shares of restricted common stock (consisting of 1,250,000 shares issued under the ROI Unit Stock Plan and 21,009 shares under the 2007 Stock Incentive Plan, as described below), with a fair value at the date of grant of $38 million were issued to IBG LLC and held as treasury stock . As of June 30, 2016 , the Company has 5,373 shares of common stock remaining to be distributed to former employees under the ROI Unit Stock Plan. 2007 Stock Incentive Plan Under the Company’s 2007 Stock Incentive Plan (the “Stock Incentive Plan”), up to 30 million shares of the Company’s common stock may be granted and issued to directors, officers, employees, contractors and consultants of the Company. The purpose of the Stock Incentive Plan is to promote the Company’s long ‑term financial success by attracting, retaining and rewarding eligible participants. As a result of the Company’s organizational structure, a description of which can be found on page 4 of the Company’s A nnual Report Form 10 - K, in Part I Item 1 , there is no dilutive effect upon ownership of common stockholders of issuing shares under the Stock Incentive Plan. The issuances do not dilute the book value of the ownership of common stockholders since the restricted stock units are granted at market value , and upon their vesting and the related issuance of shares of c ommon stock, the ownership of IBG, Inc. in IBG LLC, increases proportionately to the shares issued. As a result of such proportionate increase in share ownership, the dilution upon issuance of common stock is borne by IBG LLC’s majority member (i.e., noncontrolling interest), Holdings, and not by IBG, Inc. or its common stockholders . Additionally, dilution of earnings that may take place after issuance of common stock is reflected in EPS reported in the Company’s financial statements. The EPS dilution can be neither estimated nor projected, but historically it has not been material. The Stock Incentive Plan is administered by the Compensation Committee of the Company’s Board of Directors. The Compensation Committee has discretionary authority to determine the eligibility to participate in the Stock Incentive Plan and establishes the terms and conditions of the stock awards, including the number of awards granted to each participant and all other terms and conditions applicable to such awards in individual grant agreements. Awards are expected to be made primarily through grants of restricted common stock. Stock Incentive Plan awards are subject to issuance over time and may be forfeited upon the participant ’s termination of employment or violation of certain applicable covenants prior to issuance, unless determined otherwise by the Compensation Committee. The Stock Incentive Plan provides that, upon a change in control, the Compensation Committee may, at its discretion, fully vest any granted but not yet earned awards under the Stock Incentive Plan, or provide that any such granted but not yet earned awards will be honored or assumed, or new rights substituted by the new employer on a substantially similar basis and on terms and conditions substantially comparable to those of the Stock Incentive Plan. The Company expect s to continue to grant awards on or about December 31 of each year to eligible participants as part of an overall plan of equity compensation. Shares of common stock vest, and become distributable to participants in accordance with the following schedule: • 10% on the first vesting date, which is on or about May 9 of each year; and • an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with the Company and compliance with non-competition and other applicable covenants. Awards granted to external directors vest, and are distributed, over a five ‑year period (20% per year) commencing one year after the date of grant. A total of 22,996 shares have been granted to the external directors cumulatively since the plan inception . Stock Incentive Plan share grants (excluding 21,009 shares issued pursuant to the ROI Unit Stock Plan described above) and the related fair values since the plan inception are presented in the table below:     Fair Value at  Date of Grant  Shares ($ millions)  Prior periods (since inception) 17,284,454 $ 302  December 31, 2013 1,894,046 46  December 31, 2014 1,709,968 49  December 31, 2015 1,211,067 1 52  22,099,535 $ 449  (1) Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June, 30, 2016 .  Estimated future grants under the Stock Incentive Plan are accrued for ratably during each year (see Note 2). In accordance with the vesting schedule, outstanding awards vest and are distributed to participants yearly on or about May 9 of each year . At the end of each year, there are no vested awards that remain undistributed. Compensation expense related to the Stock Incentive Plan recognized in the condensed consolidated statements of comprehensive income was $22 million and $24 million for the six months ended June 30, 2016 and 2015 , respectively. Estimated future compensation costs for unvested awards, net of forfeiture credits, as of June 30, 2016 are $29 million. The following summarizes the Stock Incentive Plan and ROI Unit Stock Plan activities from December 31, 2015 through June 30, 2016 :     Stock ROI Unit  Incentive Plan Stock Plan  Shares (Shares)  Balance, December 31, 2015 8,937,519 1 6,370  Granted — —  Forfeited (55,653) —  Distributed (2,395,177) (997)  Balance, June 30, 2016 6,486,689 5,373  (1) Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June 30, 2016 .  Awards granted under the stock plans are subject to forfeiture in the event a participant ceases employment with the Company. The stock plans provide that participants who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post ‑employment provisions will forfeit 50% of unvested previously granted awards unless the participant is over the age of 59, in which case the participant would be eligible to receive 100% of unvested awards previously granted. Distributions of remaining awards granted on or before January 1, 2009 to former participants will occur within 90 days of the anniversary of the termination of employment date over a five (5) year vesting schedule, 12.5% in each of the first four years and 50% in the fifth year. Distributions of remaining awards granted on or after January 1, 2010 to former participants will occur over the remaining vesting schedule applicable to each grant. Through June 30, 2016 , a total of 441,802 shares have been distributed under these post ‑employment provisions. These distributions are included in the table above.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2016
Income Taxes [Abstract]
Income Taxes	10 . Income Taxes Income tax expense for the six months ended June 30, 2016 and 2015 differs from the U.S. federal statutory rate primarily due to the taxation treatment of income attributable to noncontrolling interests in IBG LLC. These noncontrolling interests are subject to U.S. taxation as partnerships. Accordingly, the income attributable to these noncontrolling interests is reported in the condensed consolidated statements of comprehensive income, but the related U.S. income tax expense attributable to these noncontrolling interests is not reported by the Company as it is the obligation of the individual partners. Income tax expense is also affected by the differing effective tax rates in foreign, state and local jurisdictions where certain of the Company’s subsidiaries are subject to corporate taxation. Deferred income taxes arise primarily due to the amortization of the deferred tax assets recognized in connection with the common stock offerings (see Note 4), differences in the valuation of financial assets and liabilities, and for other temporary differences arising from the deductibility of compensation and depreciation expenses in different time periods for book and income tax return purposes.  As of and for the six months ended June 30, 2016 and 2015 , the Company had no unrecognized tax and no valuation allowances on deferred tax assets were required. The Company is subject to taxation in the U.S. and various states and foreign jurisdictions. As of June 30, 2016, the Company is no longer subject to U.S. Federal and State income tax examinations for tax years prior to 2010, and to non-U.S. income tax examinations for tax years prior to 2006. As of June 30, 2016 , accumulated earnings held by non ‑U.S. subsidiaries totaled $1.0 billion ( as of December 31, 2015 $1.0 billion ). Of this amount, approximately $0.3 billion ( as of December 31, 2015 $0.4 billion ) is attributable to earnings of the Company ’ s foreign subsidiaries that are considered “ pass ‑through ” entities for U.S. income tax purposes. Since the Company accounts for U.S. income taxes on these earnings on a current basis, no additional U.S. tax consequences would result from the repatriation of these earnings other than that which would be due arising from currency fluctuations between the time the earnings are reported for U.S. tax purposes and when they are remitted. With respect to certain of these subsidiaries ’ accumulated earnings (approximately $0.2 billion and $0.3 billion as of June 30, 2016 and December 31, 2015 , respectively), repatriation would result in additional foreign taxes in the form of dividend withholding tax imposed on the recipient of the distribution or dividend distribution tax imposed on the payor of the distribution. The Company has not provided for its proportionate share of these additional foreign taxes as it does not intend to repatriate these earnings in the foreseeable future. For the same reason, the Company has not provided deferred U.S. tax on cumulative translation adjustments associated with these earnings. The remainder of the accumulated earnings are attributable to non ‑U.S. subsidiaries that are not considered “pass ‑through” entities for U.S. tax purposes. The Company’s U.S. tax basis in the stock of most of these entities exceeds its book basis. Establishing a deferred tax asset pursuant to ASC Topic 740 is not permitted as this difference will not reverse in the foreseeable future. In the instances in which the Company’s book basis were to exceed its U.S. tax basis, no deferred tax liability would be established as the Company would consider the earnings of those entities to be indefinitely reinvested.

Commitments, Contingencies And

Commitments, Contingencies And Guarantees	6 Months Ended
	Jun. 30, 2016
Commitments, Contingencies And Guarantees [Abstract]
Commitments, Contingencies And Guarantees	11 . Commitments, Contingencies and Guarantees  Claims Against Customers  On January 15, 2015, due to the sudden move in the value of the Swiss franc that followed an unprecedented action by the Swiss National Bank, which removed a previously instituted and repeatedly reconfirmed cap of the currency relative to the Euro, several of the Company’s customers who held currency futures and spot positions suffered losses in excess of their deposits with the Company. The Company took immediate action to hedge its exposure to the foreign currency receivables from these customers. The Company estimates the cumulative losses related to this event, net of hedging activity and debt collection efforts, to be approximately $119 million. The Company is actively pursuing collection of the debts. The ultimate effect of this incident on the Company’s results will depend upon the outcome of the Company’s debt collection efforts.  Litigation  The Company is subject to certain pending and threatened legal actions which arise out of the normal course of business. Litigation is inherently unpredictable, particularly in proceedings where claimants seek substantial or indeterminate damages, or which are in their early stages. The Company has not been able to quantify the actual loss or range of loss related to such legal proceedings, the manner in which they will be resolved, the timing of final resolution or the ultimate settlement. Management believes that the resolution of these actions will not have a material effect, if any, on the Company’s business or financial condition, but may have a material impact on the results of operations for a given period.  The Company accounts for potential losses related to litigation in accordance with FASB ASC Topic 450, “Contingencies.” As of June 30, 2016 and 2015, reserves provided for potential losses related to litigation matters were not material.  Trading Technologies Matter  On February 3, 2010, Trading Technologies International, Inc. (“Trading Technologies”) commenced an action in the U.S. District Court for the Northern District of Illinois, Eastern Division, against IBG LLC and IB LLC (“Defendants”) alleging infringement of twelve U.S. patents and seeking, among other things, unspecified damages and injunctive relief. The Defendants filed an answer denying the claims and asserted counterclaims seeking a declaration that the patents have not been infringed and are invalid. The Defendants and/or certain codefendants filed petitions with the U.S. Patent and Trademark Office (“USPTO”) for Covered Business Method (“CBM”) Review on the asserted patents. Thus far the USPTO issued decisions instituting CBM Review on six of the asserted patents and has made a finding that it is more likely than not that the patents are invalid. On February 19, 2016, the Defendants filed a motion requesting to stay the litigation in light of the CBM Review petitions. On May 9, 2016, the District Court granted the Defendants’ motion to stay the case pending the CBM Reviews. While it is too early to predict the outcome of the matter, the Company believes it has meritorious defenses to the allegations made in the complaint and intend to defend itself vigorously against them.  Class Action Matter  On December 18, 2015, a former individual customer filed a purported class action complaint against IB LLC, IBG, Inc., and Thomas Frank, PhD, the Company’s Executive Vice President and Chief Information Officer, in the U.S. District Court for the District of Connecticut. The complaint alleges that the former customer and members of the purported class of IB LLC’s customers were harmed by alleged “flaws” in the computerized system used by the Company to close out (i.e., liquidate) positions in customer brokerage accounts that have margin deficiencies. The complaint seeks, among other things, undefined compensatory damages and declaratory and injunctive relief. Table of Contents Interactive Brokers Group, Inc. and Subsidiaries Notes to Unaudited Condensed Consolidated Financial Statements 27. The Company believes that the complaint is without merit and the Company has filed a motion to dismiss it. Among other things, the Company’s customer agreement, federal law and associated industry rules grant broker-dealers broad discretion to close out margin deficient customer accounts for the broker’s protection. Further, the Company does not believe that a purported class action is appropriate given the great differences in portfolios, markets and many other circumstances surrounding the liquidation of any particular customer’s margin-deficient account. IB LLC and the related defendants intend to defend themselves vigorously against the case and, consistent with past practice in connection with this type of unwarranted action, any potential claims for counsel fees and expenses incurred in defending the case shall be fully pursued against the plaintiff.  Guarantees  Certain of the Operating Companies provide guarantees to securities clearing houses and exchanges which meet the accounting definition of a guarantee under FASB ASC Topic 460, “Guarantees.” Under standard membership agreements, clearing house and exchange members are required to guarantee collectively the performance of other members. Under the agreements, if a member becomes unable to satisfy its obligations, other members would be required to meet shortfalls. In the opinion of management, the Operating Companies’ liability under these arrangements is not quantifiable and could exceed the cash and securities they have posted as collateral. However, the potential for these Operating Companies to be required to make payments under these arrangements is remote. Accordingly, no contingent liability is carried in the condensed consolidated statements of financial condition for these arrangements.  In connection with its retail brokerage business, IB LLC or other electronic brokerage Operating Companies perform securities and commodities execution, clearance and settlement on behalf of their customers for whom they commit to settle trades submitted by such customers with the respective clearing houses. If a customer fails to fulfill its settlement obligations, the respective Operating Company must fulfill those settlement obligations. No contingent liability is carried on the condensed consolidated statements of financial condition for such customer obligations.  Other Commitments  Certain clearing houses, clearing banks and firms used by certain Operating Companies are given a security interest in certain assets of those Operating Companies held by those clearing organizations. These assets may be applied to satisfy the obligations of those Operating Companies to the respective clearing organizations. 

Segment And Geographic Informat

Segment And Geographic Information	6 Months Ended
	Jun. 30, 2016
Segment And Geographic Information [Abstract]
Segment And Geographic Information	12. Segment and Geographic Information The Company has two operating business segments: electronic brokerage and market making. These segments are supported by the corporate segment which provides centralized services and executes the Company’s currency diversification strategy.  The Company conducts its electronic brokerage business through certain Interactive Brokers subsidiaries, which provide electronic execution and clearing services to customers worldwide. The Company conducts its market making business principally through its Timber Hill subsidiaries on the world’s leading exchanges and market centers, primarily in exchange ‑traded equities, equity options and equity ‑index options and futures. Significant transactions and balances between the Operating Companies occur, primarily as a result of certain Operating Companies holding exchange or clearing organization memberships, which are utilized to provide execution and clearing services to affiliates. Charges for transactions between segments are designed to approximate full costs. Intra ‑segment and intra ‑region income and expenses and related balances have been eliminated in this segment and geographic information to reflect the external business conducted in each segment or geographic region. Corporate items include non ‑allocated corporate income and expenses that are not attributed to segments for performance measurement, net gains and losses on positions held as part of our overall currency diversification strategy, corporate assets and eliminations.  Management believes that the following information by business segment provides a reasonable representation of each segment’s contribution to total net revenues and income before income taxes for the three months and six months ended June 30, 2016 and 2015 , and to total assets as of June 30, 2016 and December 31, 2015 .     Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Net revenues  Electronic brokerage $ 310 $ 288 $ 657 $ 578  Market making 43 72 102 139  Corporate 16 27 99 (158)  Total net revenues $ 369 $ 387 $ 858 $ 559  Income before income taxes  Electronic brokerage $ 191 $ 188 $ 426 $ 239  Market making 5 30 25 57  Corporate 17 22 99 (167)  Total income before income taxes $ 213 $ 240 $ 550 $ 129      June 30, December 31,  2016 2015   (in millions)  Segment Assets  Electronic brokerage $ 46,805 $ 44,421  Market making 11,680 10,825  Corporate (6,656) (6,512)  Total assets $ 51,829 $ 48,734  The Company operates its automated global business in the U.S. and international markets on more than 100 electronic exchanges and market centers. A significant portion of the Company’s net revenues are generated by subsidiaries operating outside the U.S. International operations are comprised of electronic brokerage and market making activities in 25 countries in Europe, Asia and the Americas (outside the U.S.). The following table presents total net revenues and income before income taxes by geographic area for the three and six months ended June 30, 2016 and 2015 . The geographic analysis presented below is based on the location of the subsidiaries in which the transactions are recorded. This geographic information does not reflect the way the Company’s business is managed.      Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Net revenues  United States $ 278 $ 310 $ 682 $ 379  International 91 77 176 180  Total net revenues $ 369 $ 387 $ 858 $ 559  Income before income taxes  United States $ 177 $ 208 $ 485 $ 43  International 36 32 65 86  Total income before income taxes $ 213 $ 240 $ 550 $ 129  

Regulatory Requirements

Regulatory Requirements	6 Months Ended
	Jun. 30, 2016
Regulatory Requirements [Abstract]
Regulatory Requirements	 13 . Regulatory Requirements As of June 30, 2016 , aggregate excess regulatory capital for all of the Operating Companies was $4.0 billion. IB LLC, TH LLC and IB Corp are subject to the Uniform Net Capital Rule (Rule 15c3 ‑1) under the Exchange Act and the Commodities and Futures Trading Commission’s minimum financial requirements (Regulation 1.17), and THE is subject to the Swiss Financial Market Supervisory Authority eligible equity requirement. THA is subject to the Australian Stock Exchange liquid capital requirement, THLI is subject to the Financial Market Authority Liechtenstein eligible capital requirements, THC and IBC are subject to the Investment Industry Regulatory Organization of Canada risk adjusted capital requirement, IBUK is subject to the U.K. Financial Conduct Authority Capital Requirements Directive, IBHK is subject to the Hong Kong Securities Futures Commission liquid capital requirement, IBI is subject to the National Stock Exchange of India net capital requirements and IBSJ is subject to the Japanese Financial Supervisory Agency capital requirements. The following table summarizes capital, capital requirements and excess regulatory capital.     Net Capital/  Eligible Equity Requirement Excess   (in millions)  IB LLC $ 2,923 $ 245 $ 2,678  TH LLC 278 1 277  THE 602 190 412  Other regulated Operating Companies 655 69 586  $ 4,458 $ 505 $ 3,953  Regulatory capital requirements could restrict the Operating Companies from expanding their business and declaring dividends if their net capital does not meet regulatory requirements. Also, certain Operating Companies are subject to other regulatory restrictions and requirements. As of June 30, 2016 , all of the regulated Operating Companies were in compliance with their respective regulatory capital requirements.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2016
Related Party Transactions [Abstract]
Related Party Transactions	14 . Related Party Transactions Receivable from affiliate, reported in other assets in the condensed consolidated statement of financial condition, represents amounts advanced to Holdings and payable to affiliate represents amounts payable to Holdings under the Tax Receivable Agreement (see Note 4). Included in receivables from and payables to customers in the condensed consolidated statements of financial condition as of June 30, 2016 and December 31, 2015 were accounts receivable from directors, officers and their affiliates of $20 million and $ 85 million and payables of $771 million and $ 698 million, respectively. The Company may extend credit to these related parties in connection with margin loans. Such loans are (i) made in the ordinary course of business, (ii) are made on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable loans with persons not related to the company, and (iii) do not involve more than the normal risk of collectability or present other unfavorable features.  

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2016
Subsequent Events [Abstract]
Subsequent Events	15 . Subsequent Events As required by FASB ASC Topic 855, “ Subsequent Events,” the Company has evaluated subsequent events for adjustment to or disclosure in its condensed consolidated financial statements through the date the condensed consolidated financial statements were issued. Except as disclosed in Note 4, no other recordable or disclosable events occurred.  ***** 

Significant Accounting Polici22

Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2016
Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed consolidated financial statements are presented in U.S. dollars and have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding financial reporting with respect to Form 10 ‑Q. These condensed consolidated financial statements are unaudited and should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s 2015 Annual Report on Form 10-K for the year ended December 31, 2015, which was filed with the SEC on February 29, 2016. The condensed consolidated financial information as of December 31, 2015 has been derived from the audited consolidated financial statements not included herein. These condensed consolidated financial statements include the accounts of the Company and its consolidated subsidiaries and reflect all adjustments of a normal and recurring nature that are, in the opinion of management, necessary for the fair presentation of the results for the periods presented. The operating results for interim periods are not necessarily indicative of the operating results for the entire year.
Principles Of Consolidation, Including Noncontrolling Interests	 Principles of Consolidation, including Noncontrolling Interests  These condensed consolidated financial statements include the accounts of IBG, Inc. and its majority and wholly owned subsidiaries. As sole managing member of IBG LLC, IBG, Inc. exerts control over IBG LLC’s operations. In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, “ Consolidation, ” the Company consolidates IBG LLC’s financial statements and records the interests in IBG LLC that it does not own as noncontrolling interests. The Company’s policy is to consolidate all other entities in which it owns more than 50% unless it does not have control. All inter ‑company balances and transactions have been eliminated.
Use Of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in these condensed consolidated financial statements and accompanying notes. These estimates and assumptions are based on judgment and the best available information at the time. Therefore, actual results could differ materially from those estimates. Such estimates include the allowance for doubtful accounts, valuation of certain investments, compensation accruals, current and deferred income taxes, and contingency reserves.
Fair Value	Fair Value Substantially all of the Company’s assets and liabilities, including financial instruments are carried at fair value based on published market prices and are marked to market, or are assets and liabilities which are short ‑term in nature and are carried at amounts that approximate fair value. The Company applies the fair value hierarchy in accordance with FASB ASC Topic 820, “ Fair Value Measurement” (“ASC Topic 820”) , to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets and liabilities and the lowest priority to unobservable inputs. The three levels of the fair value hierarchy are:   Level 1 Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.  Level 2 Quoted prices in markets that are not considered to be active or financial instruments for which all significant inputs are observable, either directly or indirectly.  Level 3 Prices or valuations that require inputs that are both significant to fair value measurement and unobservable.  Financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are generally classified as Level 1 of the fair value hierarchy. The Company’s Level 1 financial instruments, which are valued using quoted market prices as published by exchanges and clearing houses or otherwise broadly distributed in active markets, include active listed stocks, options, warrants and discount certificates, and U.S. and foreign government securities. The Company does not adjust quoted prices for financial instruments classified as Level 1 of the fair value hierarchy, even in the event that the Company may hold a large position whereby a purchase or sale could reasonably impact quoted prices. Currency forward contracts are valued using broadly distributed bank and broker prices, and are classified as Level 2 of the fair value hierarchy as such instruments are not exchange ‑traded. Other securities that are not traded in active markets are also classified in Level 2 of the fair value hierarchy. Level 3 financial instruments are comprised of securities that have been delisted or otherwise are no longer tradable and have been valued by the Company based on internal estimates.
Earnings Per Share	Earnings Per Share Earnings per share (“EPS”) is computed in accordance with FASB ASC Topic 260, “ Earnings per Share .” Basic EPS is computed by dividing the net income available for common stockholders by the weighted average number of shares outstanding for that period. Diluted EPS is calculated by dividing the net income available for common stockholders by the diluted weighted average shares outstanding for that period. Diluted EPS includes the determinants of the basic EPS and, in addition, reflects the dilutive effect of shares of common stock estimated to be distributed in the future under the Company’s stock-based compensation plans, with no adjustments to net income available for common stockholders for dilutive potential common shares.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Stock ‑Based Compensation The Company follows FASB ASC Topic 718, “ Compensation - Stock Compensation” (“ASC Topic 718”) , to account for its stock ‑based compensation plans. ASC Topic 718 requires all share ‑based payments to employees to be recognized in the condensed consolidated financial statements using a fair value ‑based method. Grants, which are denominated in U.S. dollars, are communicated to employees in the year of grant, thereby establishing the fair value of each grant. The fair value of awards granted to employees are generally expensed as follows: 50% in the year of grant in recognition of plan forfeiture provisions (as described below) and the remaining 50% over the related vesting period utilizing the “graded vesting” method permitted under ASC Topic 718. In the case of “retirement eligible” employees (those employees older than 59), 100% of awards are expensed when granted. Awards granted under stock ‑based compensation plans are subject to forfeiture in the event an employee ceases employment with the Company. The plans provide that employees who discontinue employment with the Company without cause and continue to meet the terms of the plans’ post ‑employment provisions will forfeit 50% of unvested previously granted awards unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of unvested awards previously granted.
Cash And Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of deposits with banks and all highly liquid investments, with maturities of three months or less, that are not segregated and deposited for regulatory purposes or to meet margin requirements at clearing houses.
Cash And Securities - Segregated For Regulatory Purposes	Cash and Securities - Segregated for Regulatory Purposes As a result of customer activities, certain Operating Companies are obligated by rules mandated by their primary regulators to segregate or set aside cash or qualified securities to satisfy such regulations, which have been promulgated to protect customer assets. Securities segregated for regulatory purposes consisted of U.S. government securities of $14.8 billion and $15.2 billion as of June 30, 2016 and December 31, 2015, respectively, and securities purchased under agreements to resell in the amount of $4.6 billion and $0.6 billion as of June 30, 2016 and December 31, 2015, respectively, which amounts approximate fair value.
Securities Borrowed And Securities Loaned	Securities Borrowed and Securities Loaned Securities borrowed and securities loaned are recorded at the amount of the cash collateral advanced or received. Securities borrowed transactions require the Company to provide counterparties with collateral, which may be in the form of cash, letters of credit or other securities. With respect to securities loaned, the Company receives collateral, which may be in the form of cash or other securities in an amount generally in excess of the fair value of the securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as permitted contractually. It is the Company’s policy to net, in the condensed consolidated statements of financial condition, securities borrowed and securities loaned entered into with the same counterparty that meet the offsetting requirements prescribed in FASB ASC Topic 210-20, “Balance Sheet – Offsetting” (“ASC Topic 210-20”). Securities lending fees received and paid by the Company are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income.
Securities Purchased Under Agreements To Resell and Secruities Sold Under Agreements to Repurchase	Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase Securities purchased under agreements to resell, which are reported as collateralized financing transactions, are recorded at contract value, which approximates fair value. To ensure that the fair value of the underlying collateral remains sufficient, the collateral is valued daily with additional collateral obtained or excess collateral returned, as permitted under contractual provisions. It is the Company’s policy to net, in the condensed consolidated statements of financial condition, securities purchased under agreements to resell transactions and securities sold under agreements to repurchase transactions entered into with the same counterparty that meet the offsetting requirements prescribed in ASC Topic 210-20.
Financial Instruments Owned And Sold But Not Yet Purchased	Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased, at Fair Value Financial instrument transactions are accounted for on a trade date basis. Financial instruments owned and financial instruments sold, but not yet purchased are stated at fair value based upon quoted market prices. The Company’s financial instruments pledged to counterparties where the counterparty has the right, by contract or custom, to sell or repledge the financial instruments are reported as financial instruments owned and pledged as collateral in the condensed consolidated statements of financial condition. The Company also enters into currency forward contracts. These transactions, which are also accounted for on a trade date basis, are agreements to exchange a fixed amount of one currency for a specified amount of a second currency at completion of the currency forward contract term. Unrealized mark ‑to ‑market gains and losses on currency forward contracts are included in financial instruments owned, at fair value or financial instruments sold, but not yet purchased, at fair value in the condensed consolidated statements of financial condition.
Customer Receivables And Payables	Customer Receivables and Payables Customer securities transactions are recorded on a settlement date basis and customer commodities transactions are recorded on a trade date basis. Receivables from and payables to customers include amounts due on cash and margin transactions, including futures contracts transacted on behalf of customers. Securities owned by customers, including those that collateralize margin loans or other similar transactions, are not reported in the condensed consolidated statements of financial condition. Amounts receivable from customers that are determined by management to be uncollectible are recorded as customer bad debt expense in the condensed consolidated statements of comprehensive income.
Receivables From And Payables To Brokers, Dealers And Clearing Organizations	Receivables from and Payables to Brokers, Dealers and Clearing Organizations Receivables from and payables to brokers, dealers and clearing organizations include net receivables and payables from unsettled trades, including amounts related to futures and options on futures contracts executed on behalf of customers, amounts receivable for securities not delivered by the Company to the purchaser by the settlement date (“fails to deliver”) and cash deposits. Payables to brokers, dealers and clearing organizations also include amounts payable for securities not received by the Company from a seller by the settlement date (“fails to receive”).
Investments	Investments The Company makes certain strategic investments related to its business and accounts for these investments under the cost method of accounting or under the equity method of accounting as required under FASB ASC Topic 323, “ Investments - Equity Method and Joint Ventures .” Investments accounted for under the equity method, including where the investee is a limited partnership or limited liability company, are recorded at the fair value amount of the Company’s initial investment and are adjusted each period for the Company’s share of the investee’s income or loss. The Company’s share of the income or losses from equity method investments is included in other income in the condensed consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $21 million as of June 30, 2016 ( $ 3 2 million as of December 31, 2015), which are included in other assets in the condensed consolidated statements of financial condition, increase or decrease accordingly. Contributions paid to and distributions received from equity method investees are recorded as additions or reductions, respectively, to the respective investment balance. The Company also holds exchange memberships and investments in equity securities of certain exchanges, as required to qualify as a clearing member, and strategic investments in corporate stock that do not qualify for equity method accounting. Such investments, $34 million as of June 30, 2016 ($ 34 million as of December 31, 2015), are recorded at cost or, if an other ‑than ‑temporary impairment in value has occurred, at a value that reflects management’s estimate of the impairment, and are also included in other assets in the condensed consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the condensed consolidated statements of comprehensive income when such dividends are received. A judgmental aspect of accounting for investments is evaluating whether an other ‑than ‑temporary decline in the value of an investment has occurred. The evaluation of an other ‑than ‑temporary impairment is dependent on specific quantitative and qualitative factors and circumstances surrounding an investment, including recurring operating losses, credit defaults and subsequent rounds of financing. The Company’s equity investments do not have readily determinable market values. All investments are reviewed for changes in circumstances or occurrence of events that suggest the Company’s investment may not be recoverable. If an unrealized loss on any investment is considered to be other ‑than ‑temporary, the loss is recognized in the period the determination is made .
Property And Equipment	Property, Equipment and Intangible Assets Property, equipment and intangible assets, which are included in other assets in the condensed consolidated statements of financial condition, consist of leasehold improvements, computer equipment, software developed for the Company’s internal use, office furniture, equipment and acquired technology . Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Additions and improvements that extend the lives of assets are capitalized, while expenditures for repairs and maintenance are expensed as incurred. Depreciation and amortization are computed using the straight ‑line method. Equipment is depreciated over the estimated useful lives of the assets, while leasehold improvements are amortized over the lesser of the estimated economic useful life of the asset or the term of the lease. Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years Intangible assets with a finite life are amortized on a straight line basis over their estimated useful lives of three years, and tested for recoverability whenever events indicate that the carrying amounts may not be recoverable. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.
Comprehensive Income And Foreign Currency Translation	Comprehensive Income and Foreign Currency Translation The Company’s operating results are reported in the condensed consolidated statements of comprehensive income pursuant to FASB ASC Topic 220, “ Comprehensive Income. ” Comprehensive income consists of two components: net income and other comprehensive income (“OCI”). The Company’s OCI is comprised of gains and losses resulting from translating foreign currency financial statements of non-U.S. subsidiaries , net of related income taxes, where applicable. In general, the practice and intention of the Company is to reinvest the earnings of its non ‑U.S. subsidiaries in those operations, therefore tax is usually not accrued. The Company’s non ‑U.S. domiciled subsidiaries have a functional currency that is other than the U.S. dollar. Such subsidiaries’ assets and liabilities are translated into U.S. dollars at period ‑end exchange rates, and revenues and expenses are translated at average exchange rates prevailing during the period. Adjustments that result from translating amounts from a subsidiary’s functional currency to the U.S. dollar (as described above) are reported net of tax, where applicable, in accumulated OCI in the condensed consolidated statements of financial condition.
Revenue Recognition	Revenue Recognition Trading Gains Trading gains and losses are recorded on trade date and are reported on a net basis. Trading gains and losses are comprised of changes in the fair value of financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value (i.e., unrealized gains and losses) and realized gains and losses related to the Company’s market making business segment. Included in trading gains are net gains and losses on stocks, U.S. and foreign government securities, options, futures, foreign exchange and other derivative instruments. Dividends are integral to the valuation of stocks and interest is integral to the valuation of fixed income instruments. Accordingly, both dividends and interest income and expense attributable to financial instruments owned, at fair value and financial instruments sold, but not yet purchased, at fair value are reported on a net basis in trading gains in the condensed consolidated statements of comprehensive income. Commissions and Execution Fees Commissions earned for executing and clearing transactions are accrued on a trade date basis and are reported as commissions and execution fees in the condensed consolidated statements of comprehensive income. Interest Income and Expense The Company earns interest income and incurs interest expense primarily in connection with its electronic brokerage customer business and its securities lending activities, which are recorded on an accrual basis and are included in interest income and interest expense, respectively, in the condensed consolidated statements of comprehensive income. Foreign Currency Gains and Losses Currency translation refers to the gains and losses resulting from foreign currency transactions. Foreign currency translation gains and losses related to the Company’s currency diversification strategy are included in other income in the condensed consolidated statements of comprehensive income. Foreign currency translation gains and losses related to the market making core-business activities are included in trading gains in the condensed consolidated statements of comprehensive income. Electronic brokerage foreign currency translation gains and losses, arising from currency swap transactions, are included in interest income in the condensed consolidated statements of comprehensive income
Rebates	Rebates Rebates consist of volume discounts, credits or payments received from exchanges or other market centers related to the placement and/or removal of liquidity from the order flow in the marketplace. Rebates are recorded on an accrual basis and included net within execution and clearing expenses in the condensed consolidated statements of comprehensive income. Rebates received for trades executed on behalf of customers that elect tiered pricing are passed, in whole or part, to these customers; and such pass-through amounts are recorded net within commissions and execution fees in the condensed consolidated statements of comprehensive income. 
Income Taxes	Income Taxes The Company accounts for income taxes in accordance with FASB ASC Topic 740, “ Income Taxes” (“ASC Topic 740”) . The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits are based on enacted tax laws (see Note 10) and reflect management’s best assessment of estimated future taxes to be paid. The Company is subject to income taxes in both the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates. The Company recognizes interest related to income tax matters as interest income or interest expense and penalties related to income tax matters as income tax expense in the condensed consolidated statements of comprehensive income. Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of the underlying assets and liabilities. In evaluating the ability to recover deferred tax assets within the jurisdictions from which they arise, the Company considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax ‑planning strategies, and results of recent operations. In projecting future taxable income, historical results are adjusted for changes in accounting policies and incorporate assumptions including the amount of future state, federal and foreign pre-tax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax ‑planning strategies. These assumptions require significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates the Company is using to manage the underlying businesses. In evaluating the objective evidence that historical results provide, three years of cumulative operating income (loss) are considered. Deferred income taxes have not been provided for U.S. tax liabilities or for additional foreign taxes on the unremitted earnings of foreign subsidiaries that have been indefinitely reinvested. The calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax laws and regulations in a multitude of jurisdictions across the Company’s global operations. Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. The Company is not aware of any such changes that would have a material effect on the Company’s results of operations, cash flows, or financial position. The Company recognizes that a tax benefit from an uncertain tax position only when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, on the basis of the technical merits. A tax position that meets this standard is measured at the largest amount of benefit that will more likely than not be realized on settlement. The Company records tax liabilities in accordance with ASC Topic 740 and adjusts these liabilities when management’s judgment changes as a result of the evaluation of new information not previously available. Because of the complexity of some of these uncertainties, the ultimate resolution may result in payments that are different from the current estimates of these tax liabilities. These differences will be reflected as increases or decreases to income tax expense in the period in which new information becomes available.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements Following is a summary of recently issued FASB Accounting Standards Updates (“ASUs”) that have affected or may affect the Company’s condensed consolidated financial statements :    Affects Status   ASU 2014-15 Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. Effective for the annual period ending after December 15, 2016.   ASU 2015-14 Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-01 Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. Effective for fiscal years beginning after December 15, 2017.   ASU 2016-02 Leases (Topic 842) : Requires that, at lease inception, a lessee recognize a right-of-use asset, representing the right to use the underlying asset for the lease term, and a lease liability, representing the liability to make lease payments, in the statements of financial condition, among other requirements. Effective for fiscal years beginning after December 15, 2018.   ASU 2016-07 Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting. Effective beginning after December 15, 2016.   ASU 2016-08 Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net). Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-09 Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. Effective for annual reporting periods beginning after December 15, 2016.   ASU 2016-10 Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-12 Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. Effective for annual reporting periods beginning after December 15, 2017.   ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Effective for fiscal years beginning after December 15, 2019.   Adoption of those ASUs that became effective during 2015 and 2016, prior to the issuance of the Company’s condensed consolidated financial statements, did not have a material effect on these financial statements. The Company early adopted ASU 2016-09 Compensation – Stock Compensation (Topic 718), Improvements to Employee Share-Based Payment Accounting, as of April 1, 2016. This early adoption did not have a material impact on the Company’s condensed consolidated financial statements.

Equity And Earnings Per Share (

Equity And Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2016
Equity And Earnings Per Share [Abstract]
IBG LLC Ownership of Member Interests	   IBG, Inc. Holdings Total  Ownership % 16.2% 83.8% 100.0%  Membership interests 66,386,915 343,040,504 409,427,419 
Earnings Per Share Basic And Diluted	Basic earnings per share is calculated utilizing net income available for common stockholders divided by the weighted average number of shares of Class A and Class B common stock outstanding for that period.    Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)  Basic earnings per share  Net income available for common stockholders $ 27 $ 23 $ 60 $ 10  Weighted average shares of common stock outstanding  Class A 64,967,264 59,481,678 64,476,321 58,980,248  Class B 100 100 100 100  64,967,364 59,481,778 64,476,421 58,980,348  Basic earnings per share $ 0.41 $ 0.38 $ 0.93 $ 0.17  Diluted earnings per share are calculated utilizing the Company’s basic net income available for common stockholders divided by diluted weighted average shares outstanding with no adjustments to net income available to common stockholders for potentially dilutive common shares.     Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)  Diluted earnings per share  Net income available for common stockholders $ 27 $ 23 $ 60 $ 10  Weighted average shares of common stock outstanding  Class A  Issued and outstanding 64,967,264 59,481,678 64,476,321 58,980,248  Potentially dilutive common shares  Issuable pursuant to employee stock incentive plans 1,503,549 1,557,148 1,386,987 1,456,566  Class B 100 100 100 100  66,470,913 61,038,926 65,863,408 60,436,914  Diluted earnings per share $ 0.40 $ 0.37 $ 0.91 $ 0.17 

Comprehensive Income (Tables)

Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2016
Comprehensive Income Detail [Abstract]
Comprehensive Income Table	    Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions, except for shares or per share amounts)   Comprehensive income available for common stockholders $ 24 $ 27 $ 63 $ 13   Earnings per share on comprehensive income  Basic $ 0.36 $ 0.45 $ 0.97 $ 0.22  Diluted $ 0.36 $ 0.44 $ 0.95 $ 0.21  Weighted average common shares outstanding  Basic 64,967,364 59,481,778 64,476,421 58,980,348  Diluted 66,470,913 61,038,926 65,863,408 60,436,914 

Financial Assets And Financia25

Financial Assets And Financial Liabilities (Tables)	6 Months Ended
	Jun. 30, 2016
Financial Assets And Financial Liabilities [Abstract]
Fair Value Table	   Financial Assets At Fair Value as of June 30, 2016   Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 14,753 $ — $ — $ 14,753  Financial instruments owned  Stocks 1,943 — — 1,943  Options 1,742 — — 1,742  Warrants and discount certificates 52 — — 52  U.S. and foreign government securities 490 — — 490  Corporate and municipal bonds — 3 — 3  Currency forward contracts — 24 — 24  Total financial instruments owned, at fair value 4,227 27 — 4,254  Total financial assets at fair value $ 18,980 $ 27 $ — $ 19,007      Financial Liabilities At Fair Value as of June 30, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 1,567 $ — $ — $ 1,567  Options 1,296 — — 1,296  Warrants and discount certificates 2 — — 2  Currency forward contracts — 9 — 9  Total financial instruments sold, but not yet purchased, at fair value 2,865 9 — 2,874  Total financial liabilities at fair value $ 2,865 $ 9 $ — $ 2,874        Financial Assets At Fair Value as of December 31, 2015  Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 15,214 $ — $ — $ 15,214  Financial instruments owned, at fair value  Stocks 1,650 — — 1,650  Options 1,156 — — 1,156  Warrants and discount certificates 81 — — 81  U.S. and foreign government securities 527 — — 527  Corporate and municipal bonds — 3 — 3  Currency forward contracts — 3 — 3  Total financial instruments owned, at fair value 3,414 6 — 3,420  Total financial assets at fair value $ 18,628 $ 6 $ — $ 18,634        Financial Liabilities At Fair Value as of December 31, 2015  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 1,565 $ — $ — $ 1,565  Options 1,042 — — 1,042  Warrants and discount certificates 1 — — 1  Currency forward contracts — 9 — 9  Total financial instruments sold, but not yet purchased, at fair value 2,608 9 — 2,617  Total financial liabilities at fair value $ 2,608 $ 9 $ — $ 2,617 
Trading Gains From Market Making Transactions	   Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Equities $ 35 $ 70 $ 85 $ 121  Fixed income — — — —  Foreign exchange (1) (3) 1 8  Total trading gains, net $ 34 $ 67 $ 86 $ 129 
Financial Assets and Liabilities Not Measured at Fair Value	   June 30, 2016  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,443 $ 1,443 $ 1,443 $ - $ -  Cash and securities segregated for regulatory purposes 10,504 10,504 5,891 4,613 -  Securities borrowed 3,760 3,760 - 3,760 -  Securities purchased under agreements to resell 113 113 - 113 -  Receivables from customer 15,137 15,137 - 15,137 -  Receivables from broker, dealers, and clearing organizations 1,351 1,351 - 1,351 -  Interest receivable 58 58 - 58 -  Other assets 29 31 - 31 -  Total financial assets, not measured at fair value $ 32,395 $ 32,397 $ 7,334 $ 25,063 $ —       Financial liabilities, not measured at fair value  Short-term borrowings $ 8 $ 8 $ - $ 8 $ -  Securities loaned 3,270 3,270 - 3,270 -  Payables to customer 39,319 39,319 - 39,319 -  Payables to brokers, dealers and clearing organizations 286 286 - 286 -  Interest payable 4 4 - 4 -  Total financial liabilities, not measured at fair value $ 42,887 $ 42,887 $ - $ 42,887 $ -       December 31, 2015  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,601 $ 1,601 $ 1,601 $ - $ -  Cash and securities segregated for regulatory purposes 6,095 6,095 5,533 562 -  Securities borrowed 3,924 3,924 - 3,924 -  Securities purchased under agreements to resell 195 195 - 195 -  Receivables from customer 17,050 17,050 - 17,050  Receivables from broker, dealers, and clearing organizations 692 692 - 692 -  Interest receivable 63 63 - 63 -  Other assets 28 31 - 31 -  Total financial assets, not measured at fair value $ 29,648 $ 29,651 $ 7,134 $ 22,517 $ —         Financial liabilities, not measured at fair value  Securities loaned $ 2,894 $ 2,894 $ - $ 2,894 $ -  Payables to customer 37,084 37,084 - 37,084 -  Payables to brokers, dealers and clearing organizations 423 423 - 423 -  Interest payable 3 3 - 3 -  Total financial liabilities, not measured at fair value $ 40,404 $ 40,404 $ — $ 40,404 $ — 
Netting Of Financial Assets And Financial Liabilities	    June 30, 2016  Gross Amounts Net Amounts Amounts Not Offset  Amounts Offset in the Presented in in the Condensed  of Financial Condensed Condensed Consolidated Statement  Assets and Consolidated Consolidated of Financial Condition  Liabilities Statement of Statement of Cash or Financial  Recognized Financial Condition 2 Financial Condition Instruments Net Amount   (in millions)  Offsetting of Financial Assets  Securities segregated for regulatory purposes - purchased under agreements to resell $ 4,613 1 $ — $ 4,613 $ (4,613) $ —  Securities borrowed 3,760 — 3,760 (3,644) 116  Securities purchased under agreements to resell 113 — 113 (113) —  Financial Instruments owned, at fair value  Options 1,742 — 1,742 (1,219) 523  Warrants and discount certificates 52 — 52 (2) 50  Currency forward contracts 24 — 24 — 24  Total $ 10,304 $ — $ 10,304 $ (9,591) $ 713     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 3,270 $ — $ 3,270 $ (3,168) $ 102  Financial instruments sold, but not yet purchased, at fair value  Options 1,296 — 1,296 (1,219) 77  Warrants and discount certificates 2 — 2 (2) —  Currency forward contracts 9 — 9 — 9  Total $ 4,577 $ — $ 4,577 $ (4,389) $ 188       December 31, 2015  Gross Amounts Net Amounts Amounts Not Offset  Amounts Offset in the Presented in in the Condensed  of Financial Condensed Condensed Consolidated Statement  Assets and Consolidated Consolidated of Financial Condition  Liabilities Statement of Statement of Cash or Financial  Recognized Financial Condition 2 Financial Condition Instruments Net Amount   (in millions)  Offsetting of Financial Assets  Securities segregated for regulatory purposes - purchased under agreements to resell $ 562 1 $ — $ 562 $ (562) $ —  Securities borrowed 3,924 — 3,924 (3,816) 108  Securities purchased under agreements to resell 195 — 195 (195) —  Financial Instruments owned, at fair value  Options 1,156 — 1,156 (1,032) 124  Warrants and discount certificates 81 — 81 (1) 80  Currency forward contracts 3 — 3 — 3  Total $ 5,921 $ — $ 5,921 $ (5,606) $ 315     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 2,894 $ — $ 2,894 $ (2,773) $ 121  Financial instruments sold, but not yet purchased, at fair value  Options 1,042 — 1,042 (1,032) 10  Warrants and discount certificates 1 — 1 (1) —  Currency forward contracts 9 — 9 — 9  Total $ 3,946 $ — $ 3,946 $ (3,806) $ 140   (1) As of June 30, 2016 and December 31, 2015, the Company had $4.6 billion and $0.6 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in “Cash and securities - segregated for regulatory purposes” in the condensed consolidated statements of financial condition. (2) The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at June 30, 2016 and December 31, 2015.
Schedule of Securities Financing Transactions	    June 30, 2016  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 3,248 $ - $ - $ - $ 3,248  Corporate bonds 22 - - - 22  Total $ 3,270 $ - $ - $ - $ 3,270       December 31, 2015  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 2,873 $ - $ - $ - $ 2,873  Corporate bonds 21 - - - 21  Total $ 2,894 $ - $ - $ - $ 2,894 

Collateralized Transactions (Ta

Collateralized Transactions (Tables)	6 Months Ended
	Jun. 30, 2016
Disclosure Collateralized Transactions [Abstract]
Amounts Related To Collateralized Transactions	   June 30, 2016 December 31, 2015  Permitted Sold or Permitted Sold or  to Repledge Repledged to Repledge Repledged   (in millions)  Securities lending transactions $ 11,809 $ 3,743 $ 12,131 $ 2,229  Securities purchased under agreements to resell transactions (1) 4,724 4,724 757 743  Customer margin assets 13,806 6,989 14,905 6,279  $ 30,339 $ 15,456 $ 27,793 $ 9,251  (1) As of June 30, 2016 , $4.6 billion or 98% ( 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 customer s in accordance with SEC Rule 15c3-3.
Financial Instruments Owned and Pledged as Collateral (table)	   June 30, December 31,  2016 2015   (in millions)  Stocks $ 1,186 $ 915  U.S. and foreign government securities 488 518  $ 1,674 $ 1,433 

Other Income (Tables)

Other Income (Tables)	6 Months Ended
	Jun. 30, 2016
Other Income [Abstract]
Schedule Of Components Of Other Income	   Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Payments for order flow $ 3 $ 4 $ 7 $ 8  Market data fees 8 6 17 13  Account activity fees 5 4 9 8  Risk exposure fees 4 7 9 11  Gains on financial instruments, at fair value and other investments, net 16 3 51 35  Gains (losses) from currency diversification strategy, net 17 25 101 (162)  Other, net 4 6 7 10  $ 57 $ 55 $ 201 $ (77) 

Employee Incentive Plans (Table

Employee Incentive Plans (Tables)	6 Months Ended
	Jun. 30, 2016
Employee Incentive Plans [Abstract]
Share Grants And Fair Value	   Fair Value at  Date of Grant  Shares ($ millions)  Prior periods (since inception) 17,284,454 $ 302  December 31, 2013 1,894,046 46  December 31, 2014 1,709,968 49  December 31, 2015 1,211,067 1 52  22,099,535 $ 449  (1) Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June, 30, 2016 .
2007 Stock Incentive Plan, ROI Summary	   Stock ROI Unit  Incentive Plan Stock Plan  Shares (Shares)  Balance, December 31, 2015 8,937,519 1 6,370  Granted — —  Forfeited (55,653) —  Distributed (2,395,177) (997)  Balance, June 30, 2016 6,486,689 5,373  (1) Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June 30, 2016 .

Segment And Geographic Inform29

Segment And Geographic Information (Tables)	6 Months Ended
	Jun. 30, 2016
Segment And Geographic Information [Abstract]
Segment And Geographic Information	   Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Net revenues  Electronic brokerage $ 310 $ 288 $ 657 $ 578  Market making 43 72 102 139  Corporate 16 27 99 (158)  Total net revenues $ 369 $ 387 $ 858 $ 559  Income before income taxes  Electronic brokerage $ 191 $ 188 $ 426 $ 239  Market making 5 30 25 57  Corporate 17 22 99 (167)  Total income before income taxes $ 213 $ 240 $ 550 $ 129      June 30, December 31,  2016 2015   (in millions)  Segment Assets  Electronic brokerage $ 46,805 $ 44,421  Market making 11,680 10,825  Corporate (6,656) (6,512)  Total assets $ 51,829 $ 48,734 
Schedule Of Total Net Revenues And Income Before Income Taxes By Geographic Area	   Three Months Ended June 30, Six Months Ended June 30,  2016 2015 2016 2015   (in millions)  Net revenues  United States $ 278 $ 310 $ 682 $ 379  International 91 77 176 180  Total net revenues $ 369 $ 387 $ 858 $ 559  Income before income taxes  United States $ 177 $ 208 $ 485 $ 43  International 36 32 65 86  Total income before income taxes $ 213 $ 240 $ 550 $ 129 

Regulatory Requirements (Tables

Regulatory Requirements (Tables)	6 Months Ended
	Jun. 30, 2016
Regulatory Requirements [Abstract]
Summary Of Capital, Capital Requirements And Excess Capital	   Net Capital/  Eligible Equity Requirement Excess   (in millions)  IB LLC $ 2,923 $ 245 $ 2,678  TH LLC 278 1 277  THE 602 190 412  Other regulated Operating Companies 655 69 586  $ 4,458 $ 505 $ 3,953 

Organization and Nature of Bu31

Organization and Nature of Business (Details)	6 Months Ended
	Jun. 30, 2016employeesegment	Jul. 26, 2016	May 03, 2007
Organization And Nature Of Business [Abstract]
IBG Inc. ownership % of IBG LLC	16.20%	16.60%	10.00%
Number of employees | employee	1,169
Number of operating segments | segment	2

Significant Accounting Polici32

Significant Accounting Policies (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	May 03, 2007
SIP expense - Year of grant			50.00%
SIP expense - Remaining vesting period			50.00%
SIP expense - Employees over 59 in year of grant			100.00%
Percent of shares forfeited post employment			50.00%
Over 59 percent of shares eligible			100.00%
U.S. Treasury Securities	$ 14,800	$ 15,200
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	4,600	600
Equity method investments	21	32
Cost method investments	$ 34	$ 34
Property and equipment useful lives, description	Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years Intangible assets with a finite life are amortized on a straight line basis over their estimated useful lives of three years, and tested for recoverability whenever events indicate that the carrying amounts may not be recoverable. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years.
Maximum [Member] | Computer Equipment [Member]
Property and equipment useful lives	5 years
Maximum [Member] | Office Furniture And Equipment [Member]
Property and equipment useful lives	7 years
Maximum [Member] | Internally Developed Software [Member]
Property and equipment useful lives	3 years
Maximum [Member] | Finite-Lived Intangible Assets [Member]
Property and equipment useful lives	3 years
Minimum [Member] | Computer Equipment [Member]
Property and equipment useful lives	3 years
Minimum [Member] | Office Furniture And Equipment [Member]
Property and equipment useful lives	5 years

Equity And Earnings Per Share33

Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 26, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2010	Dec. 31, 2015	Jun. 30, 2016	May 03, 2007
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC	16.60%	16.20%				16.20%	10.00%
IBG Holdings ownership % of IBG LLC		83.80%				83.80%	90.00%
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
Preferred stock shares issued		0			0	0
Preferred stock shares outstanding		0			0	0
Amortization period DTA (years)		15 years
Unamortized deferred tax asset arising from equity offerings		$ 275			$ 288	$ 275
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		$ 460				460
Tax savings owed to IBG Holdings LLC		391				391
Tax savings retained by IBG Inc.		69				69
Tax savings paid to IBG Holdings LLC						116
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 For Membership Exchange		$ 306				$ 306
Shares Issued	1,596,200				11,047,295
Thomas Peterffy and Affiliates Ownership		88.70%				88.70%	84.60%
Distribution from IBG LLC		$ 197
Cash distribution to IBG, Inc.		$ 32
Dividend per share		$ 0.10
Dividends paid to common shareholders		$ 13	$ 12
Declaration Date		Jul. 19, 2016
Payment Date		Sep. 14, 2016
Record Date		Sep. 1, 2016
Common Class A
Equity And Earnings Per Share [Line Items]
Common stock, par value		$ 0.01			$ 0.01	$ 0.01
Shares authorized		1,000,000,000			1,000,000,000	1,000,000,000
Common stock, shares issued		66,516,360			64,121,150	66,516,360
Common stock, shares outstanding		65,671,645			63,985,335	65,671,645
Common Class B
Equity And Earnings Per Share [Line Items]
Shares authorized		100			100	100
Common stock, shares issued		100			100	100
Common stock, shares outstanding		100			100	100

Equity And Earnings Per Share34

Equity And Earnings Per Share (Basic Table) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic earnings per share:
Net income available for common stockholders	$ 27	$ 23	$ 60	$ 10
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	64,967,364	59,481,778	64,476,421	58,980,348
Basic earnings per share	$ 0.41	$ 0.38	$ 0.93	$ 0.17
Common Class A
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	64,967,264	59,481,678	64,476,321	58,980,248
Common Class B
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

Equity And Earnings Per Share35

Equity And Earnings Per Share (Diluted Table) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Diluted earnings per share:
Net income available for common stockholders	$ 27	$ 23	$ 60	$ 10
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	64,967,364	59,481,778	64,476,421	58,980,348
Potentially dilutive common shares:
Issuable pursuant to employee incentive plans	1,503,549	1,557,148	1,386,987	1,456,566
Weighted Average Number of Shares Outstanding, Diluted	66,470,913	61,038,926	65,863,408	60,436,914
Earnings Per Share, Diluted	$ 0.40	$ 0.37	$ 0.91	$ 0.17
Common Class A
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	64,967,264	59,481,678	64,476,321	58,980,248
Common Class B
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	100	100	100	100

IBG LLC Ownership of Member Int

IBG LLC Ownership of Member Interests (Table) (Details)	Jun. 30, 2016shares
IBG Inc [Member]
Ownership Percentage	16.20%
Membership Interests	66,386,915
Holdings [Member]
Ownership Percentage	83.80%
Membership Interests	343,040,504

Comprehensive Income (Details)

Comprehensive Income (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Comprehensive Income Detail [Abstract]
Comprehensive income available for common stockholders	$ 24	$ 27	$ 63	$ 13
Earnings per share on comprehensive income:
Basic	$ 0.36	$ 0.45	$ 0.97	$ 0.22
Diluted	$ 0.36	$ 0.44	$ 0.95	$ 0.21
Weighted average common shares outstanding:
Weighted Average Number of Shares Outstanding, Basic	64,967,364	59,481,778	64,476,421	58,980,348
Weighted Average Number of Shares Outstanding, Diluted	66,470,913	61,038,926	65,863,408	60,436,914

Financial Assets And Financia38

Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Billions	Jun. 30, 2016	Dec. 31, 2015
Financial Assets And Financial Liabilities [Abstract]
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	$ 4.6	$ 0.6

Financial Assets And Financia39

Financial Assets And Financial Liabilities (Fair Value Table) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities segregated for regulatory purposes	$ 14,753	$ 15,214
Total financial instruments owned, at fair value	4,254	3,420
Total Financial Assets at Fair Value	19,007	18,634
Financial instruments sold, not yet purchased, at fair value	2,874	2,617
Total Financial Liabilities at Fair Value	2,874	2,617
Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1,943	1,650
Financial instruments sold, not yet purchased, at fair value	1,567	1,565
Options owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1,742	1,156
Financial instruments sold, not yet purchased, at fair value	1,296	1,042
Warrants And Discount Certificates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	52	81
Financial instruments sold, not yet purchased, at fair value	2	1
U.S. And Foreign Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	490	527
Corporate And Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	3	3
Currency Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	24	3
Financial instruments sold, not yet purchased, at fair value	9	9
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities segregated for regulatory purposes	14,753	15,214
Total financial instruments owned, at fair value	4,227	3,414
Total Financial Assets at Fair Value	18,980	18,628
Financial instruments sold, not yet purchased, at fair value	2,865	2,608
Total Financial Liabilities at Fair Value	2,865	2,608
Level 1 | Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1,943	1,650
Financial instruments sold, not yet purchased, at fair value	1,567	1,565
Level 1 | Options owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1,742	1,156
Financial instruments sold, not yet purchased, at fair value	1,296	1,042
Level 1 | Warrants And Discount Certificates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	52	81
Financial instruments sold, not yet purchased, at fair value	2	1
Level 1 | U.S. And Foreign Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	490	527
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	27	6
Total Financial Assets at Fair Value	27	6
Financial instruments sold, not yet purchased, at fair value	9	9
Total Financial Liabilities at Fair Value	9	9
Level 2 | Corporate And Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	3	3
Level 2 | Currency Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	24	3
Financial instruments sold, not yet purchased, at fair value	$ 9	$ 9

Financial Assets And Financia40

Financial Assets And Financial Liabilities (Trading Gains from Market Making Transactions) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Financial Assets And Financial Liabilities [Abstract]
Equities	$ 35	$ 70	$ 85	$ 121
Foreign Exchange	(1)	(3)	1	8
Trading gains	$ 34	$ 67	$ 86	$ 129

Financial Assets And Financia41

Financial Assets And Financial Liabilities (Financial Assets and Liabilities Not Measured at Fair Value) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Cash and cash equivalents	$ 1,443	$ 1,601	$ 1,041	$ 1,269
Cash and securities segregated for regulatory purposes	25,257	21,309
Securities Borrowed	3,760	3,924
Securities purchased under agreements to resell	113	195
Receivables from customer	15,137	17,050
Receivables from brokers, dealers and clearing organizations	1,351	692
Interest receivable	58	63
Other Assets	456	480
Short-term borrowings	8
Securities Loaned	3,270	2,894
Payables to customer	39,319	37,084
Payables to brokers, dealers and clearing organizations	286	423
Interest payable	4	3
at Fair Value
Cash and cash equivalents	1,443	1,601
Cash and securities segregated for regulatory purposes	10,504	6,095
Securities Borrowed	3,760	3,924
Securities purchased under agreements to resell	113	195
Receivables from customer	15,137	17,050
Receivables from brokers, dealers and clearing organizations	1,351	692
Interest receivable	58	63
Other Assets	31	31
Total financial assets, not measured at fair value	32,397	29,651
Short-term borrowings	8
Securities Loaned	3,270	2,894
Payables to customer	39,319	37,084
Payables to brokers, dealers and clearing organizations	286	423
Interest payable	4	3
Total financial liabilities, not measured at fair value	42,887	40,404
Carrying Value
Cash and cash equivalents	1,443	1,601
Cash and securities segregated for regulatory purposes	10,504	6,095
Securities Borrowed	3,760	3,924
Securities purchased under agreements to resell	113	195
Receivables from customer	15,137	17,050
Receivables from brokers, dealers and clearing organizations	1,351	692
Interest receivable	58	63
Other Assets	29	28
Total financial assets, not measured at fair value	32,395	29,648
Short-term borrowings	8
Securities Loaned	3,270	2,894
Payables to customer	39,319	37,084
Payables to brokers, dealers and clearing organizations	286	423
Interest payable	4	3
Total financial liabilities, not measured at fair value	42,887	40,404
Level 1
Cash and cash equivalents	1,443	1,601
Cash and securities segregated for regulatory purposes	5,891	5,533
Total financial assets, not measured at fair value	7,334	7,134
Short-term borrowings
Securities Loaned
Payables to customer
Payables to brokers, dealers and clearing organizations
Interest payable
Total financial liabilities, not measured at fair value
Level 2
Cash and securities segregated for regulatory purposes	4,613	562
Securities Borrowed	3,760	3,924
Securities purchased under agreements to resell	113	195
Receivables from customer	15,137	17,050
Receivables from brokers, dealers and clearing organizations	1,351	692
Interest receivable	58	63
Other Assets	31	31
Total financial assets, not measured at fair value	25,063	22,517
Short-term borrowings	8
Securities Loaned	3,270	2,894
Payables to customer	39,319	37,084
Payables to brokers, dealers and clearing organizations	286	423
Interest payable	4	3
Total financial liabilities, not measured at fair value	42,887	40,404
Level 3
Cash and cash equivalents
Cash and securities segregated for regulatory purposes
Securities Borrowed
Securities purchased under agreements to resell
Receivables from customer
Receivables from brokers, dealers and clearing organizations
Interest receivable
Other Assets
Total financial assets, not measured at fair value
Short-term borrowings
Securities Loaned
Payables to customer
Payables to brokers, dealers and clearing organizations
Interest payable
Total financial liabilities, not measured at fair value

Financial Assets And Financia42

Financial Assets And Financial Liabilities (Netting of Financial Assets) (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Securities, Segregated For Regulatory Purposes, Purchased Under Agreements To Resell [Abstract]
Gross Amounts of Financial Assets Recognized	[1]	$ 4,613	$ 562
Amounts Offset in the Condensed Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		4,613	562
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(4,613)	(562)
Offsetting Securities Borrowed [Abstract]
Gross Amounts of Financial Assets Recognized		3,760	3,924
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		3,760	3,924
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(3,644)	(3,816)
Net Amount		116	108
Offsetting Securities Purchased under Agreements to Resell [Abstract]
Gross Amounts of Financial Assets Recognized		113	195
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		113	195
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(113)	(195)
Total [Abstract]
Gross Amounts of Financial Assets Recognized		10,304	5,921
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		10,304	5,921
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(9,591)	(5,606)
Net Amount		713	315
Options [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		1,742	1,156
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		1,742	1,156
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(1,219)	(1,032)
Net Amount		523	124
Warrants And Discount Certificates [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		52	81
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		52	81
Amounts Not Offset in the Condensed Consolidated Statement of Financial Condition: Cash or Financial Instruments		(2)	(1)
Net Amount		50	80
Currency Forward Contracts [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		24	3
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition		24	3
Net Amount		$ 24	$ 3
[1]	As of June 30, 2016 and December 31, 2015, the Company had $4.6 billion and $0.6 billion, respectively, of securities purchased under agreements to resell that were segregated to satisfy regulatory requirements. These securities are included in "Cash and securities - segregated for regulatory purposes" in the condensed consolidated statements of financial condition.
[2]	The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at June 30, 2016 and December 31, 2015.

Financial Assets And Financia43

Financial Assets And Financial Liabilities (Netting of Financial Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Offsetting Securities Loaned [Abstract]
Gross Amounts of Financial Assets Recognized	$ 3,270	$ 2,894
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition	3,270	2,894
Amounts of Liabilities Not Offset in the Condensed Consolidated Statement of Financial Condition (Cash or Financial Instruments)	(3,168)	(2,773)
Net Amount	102	121
Total [Abstract]
Gross Amounts of Financial Assets Recognized	4,577	3,946
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition	4,577	3,946
Amounts of Liabilities Not Offset in the Condensed Consolidated Statement of Financial Condition (Cash or Financial Instruments)	(4,389)	(3,806)
Net Amount	188	140
Options [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized	1,296	1,042
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition	1,296	1,042
Amounts of Liabilities Not Offset in the Condensed Consolidated Statement of Financial Condition (Cash or Financial Instruments)	(1,219)	(1,032)
Net Amount	77	10
Warrants And Discount Certificates [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized	2	1
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition	2	1
Amounts of Liabilities Not Offset in the Condensed Consolidated Statement of Financial Condition (Cash or Financial Instruments)	(2)	(1)
Currency Forward Contracts [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized	9	9
Amounts Offset in the Condensed Consolidated Statement of Financial Condition
Net Amounts Presented in Condensed Consolidated Statement of Financial Condition	9	9
Net Amount	$ 9	$ 9

Financial Assets And Financia44

Financial Assets And Financial Liabilities (Secured Financing Transactions) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	$ 3,270	$ 2,894
Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	3,270	2,894
Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	3,248	2,873
Common Stock [Member] | Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	3,248	2,873
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	22	21
Corporate Bonds [Member] | Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Loaned	$ 22	$ 21

Collateralized Transactions (Na

Collateralized Transactions (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Disclosure Collateralized Transactions [Abstract]
Customers receivables	$ 15,137	$ 17,050
Securities repledged and deposited for customers	$ 4,600	$ 600
Percentage of securities repledged and deposited for customers	98.00%	76.00%

Collateralized Transactions (Am

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Permitted To Repledge [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		$ 11,809	$ 12,131
Agreements to resell	[1]	4,724	757
Customer margin assets		13,806	14,905
Total collateralized transactions		30,339	27,793
Sold Or Repledged [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		3,743	2,229
Agreements to resell	[1]	4,724	743
Customer margin assets		6,989	6,279
Total collateralized transactions		$ 15,456	$ 9,251
[1]	As of June 30, 2016, $4.6 billion or 98% (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.

Collateralized Transactions (Fi

Collateralized Transactions (Financial instruments owned and pledged where the counterparty has the right to repledge) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Disclosure Collateralized Transactions [Abstract]
Stocks	$ 1,186	$ 915
U.S. and foreign government securities	488	518
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$ 1,674	$ 1,433

Other Income (Schedule Of Compo

Other Income (Schedule Of Components Of Other Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Other Income [Abstract]
Payments for order flow	$ 3	$ 4	$ 7	$ 8
Market data fees	8	6	17	13
Account activity fees	5	4	9	8
Risk exposure fees	4	7	9	11
Gains on financial instruments, at fair value and other investments, net	16	3	51	35
Gains (losses) from currency diversification strategy, net	17	25	101	(162)
Other, net	4	6	7	10
Other income	$ 57	$ 55	$ 201	$ (77)

Employee Incentive Plans (Narra

Employee Incentive Plans (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended	110 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jun. 30, 2016	May 03, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
401(k) plan contribution expense	$ 2	$ 1
Common Stock Shares issued under ROI Unit Stock Plan					1,271,009
ROI Shares issued to IBG LLC					1,250,000
2007 SIP shares issued under ROI Unit Stock Plan					21,009
Fair value ROI Treasury Stock					$ 38
Common stock to be distributed to former employees under the ROI Unit Stock Plan	5,373
Maximum shares of stock distributable under 2007 Stock Incentive Plan	30,000,000			30,000,000
Shares granted to external directors				22,996
Stock Incentive Plan Granted Shares Adjustment			11,988
2007 Stock Incentive Plan Compensation Expense	$ 22	$ 24
Estimated Future 2007 Stock Incentive Plan Compensation Expense	$ 29			$ 29
Percent Shares Forfeited Post Employment					50.00%
Over Fifty Nine Percent Unvested Shares Eligible					100.00%
Former employees vesting schedule (Years)	5 years
Post employment vesting percentage (Years 1 - 4)					12.50%
Post employment vesting percentage (Year 5)					50.00%
Post employment shares distribution				441,802
2007 Stock Incentive Plan (Shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage	• 10% on the first vesting date, which is on or about May 9 of each year; and• an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with the Company and compliance with non-competition and other applicable covenants.

Employee Incentive Plans (Share

Employee Incentive Plans (Share Grants And Fair Value) (Details) - USD ($) $ in Millions	12 Months Ended				68 Months Ended	110 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2016
Employee Incentive Plans [Abstract]
Shares granted	1,211,067	[1]	1,709,968	1,894,046	17,284,454
Fair Value - Date of Grant	$ 52		$ 49	$ 46	$ 302
Shares Granted IPO to Date						22,099,535
Fair Value - Date of Grant IPO to Date						$ 449
[1]	Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June, 30, 2016.

Employee Incentive Plans (2007

Employee Incentive Plans (2007 Stock Incentive Plan, ROI Summary) (Details)	6 Months Ended
	Jun. 30, 2016shares
2007 Stock Incentive Plan (Shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance	8,937,519	[1]
Shares Forfeited	(55,653)
Shares Distributed	(2,395,177)
Ending Balance	6,486,689
2007 ROI Unit Stock Plan (Shares) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance	6,370
Shares Distributed	(997)
Ending Balance	5,373
[1]	Stock Incentive Plan number of granted shares related to 2015 was adjusted by 11,988 additional shares during the six months ended June 30, 2016.

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Billions	Jun. 30, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Undistributed accumulated earnings of foreign subsidiaries	$ 1	$ 1
Accumulated earnings of foreign pass through subsidiaries	0.3	0.4
Accumulated earnings subject to additional foreign tax	$ 0.2	$ 0.3

Commitments, Contingencies an53

Commitments, Contingencies and Guarantees (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016USD ($)
Commitments, Contingencies And Guarantees [Abstract]
Net Loss from Unsecured Customer Receivables	$ 119

Segment And Geographic Inform54

Segment And Geographic Information (Segment Table) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total net revenues	$ 369	$ 387	$ 858	$ 559
Income before Income Taxes	213	240	550	129
Assets	51,829		51,829		$ 48,734
Electronic Brokerage [Member]
Segment Reporting Information [Line Items]
Total net revenues	310	288	657	578
Income before Income Taxes	191	188	426	239
Assets	46,805		46,805		44,421
Market Making [Member]
Segment Reporting Information [Line Items]
Total net revenues	43	72	102	139
Income before Income Taxes	5	30	25	57
Assets	11,680		11,680		10,825
Corporate And Eliminations [Member]
Segment Reporting Information [Line Items]
Total net revenues	16	27	99	(158)
Income before Income Taxes	17	$ 22	99	$ (167)
Assets	$ (6,656)		$ (6,656)		$ (6,512)

Segment And Geographic Inform55

Segment And Geographic Information (Geographic Table) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Total net revenues	$ 369	$ 387	$ 858	$ 559
Income before Income Taxes	213	240	550	129
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues	278	310	682	379
Income before Income Taxes	177	208	485	43
International [Member]
Segment Reporting Information [Line Items]
Total net revenues	91	77	176	180
Income before Income Taxes	$ 36	$ 32	$ 65	$ 86

Regulatory Requirements (Narrat

Regulatory Requirements (Narrative) (Details) $ in Millions	Jun. 30, 2016USD ($)
Regulatory Requirements [Abstract]
Excess regulatory capital	$ 3,953

Regulatory Requirements (Summar

Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) $ in Millions	Jun. 30, 2016USD ($)
Net Capital / Eligible Equity	$ 4,458
Required net capital	505
Excess regulatory capital	3,953
IB LLC [Member]
Net Capital / Eligible Equity	2,923
Required net capital	245
Excess regulatory capital	2,678
TH LLC [Member]
Net Capital / Eligible Equity	278
Required net capital	1
Excess regulatory capital	277
THE [Member]
Net Capital / Eligible Equity	602
Required net capital	190
Excess regulatory capital	412
Other Regulated Operating Companies [Member]
Net Capital / Eligible Equity	655
Required net capital	69
Excess regulatory capital	$ 586

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Related Party Transactions [Abstract]
Due from Related Parties - Customers	$ 20	$ 85
Due to Related Parties - Customers	$ 771	$ 698