Interactive Brokers (IBKR) 10-K 1 Mar 18 2017 FY Annual report Financial data

Documentation and Entity Inform

Documentation and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Entity Registrant Name	Interactive Brokers Group, Inc.
Entity Central Index Key	1,381,197
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Fiscal Year Focus	2,017
Fiscal Period Focus	FY
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
Entity Public Float			$ 2,544,471,315
Common Class A
Common Stock Shares Outstanding		71,475,755
Common Class B
Common Stock Shares Outstanding		100

Consolidated Statements of Fina

Consolidated Statements of Financial Condition - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 1,732	$ 1,925
Cash and securities segregated for regulatory purposes	20,232	24,017
Securities borrowed	2,957	3,629
Securities purchased under agreements to resell	2,035	111
Financial instruments owned, at fair value:
Financial instruments owned	1,950	2,104
Financial instruments owned and pledged as collateral	1,204	1,933
Total financial instruments owned, at fair value	3,154	4,037
Receivables:
Customers, less allowance for doubtful accounts of $40 and $97 as of December 31, 2017 and 2016	29,821	19,409
Receivables from brokers, dealers and clearing organizations	823	1,040
Interest receivable	116	57
Total receivables	30,760	20,506
Other assets	292	448
Total assets	61,162	54,673
Liabilities and equity
Short-term borrowings	15	74
Securities loaned	4,444	4,293
Securities sold under agreements to repurchase	1,316
Financial instruments sold, not yet purchased, at fair value	767	2,145
Payables:
Payables to customers	47,548	41,731
Payables to brokers, dealers and clearing organizations	283	239
Payable to affiliate	187	285
Accounts payable, accrued expenses and other liabilities	147	80
Interest payable	22	6
Total payables	48,187	42,341
Total liabilities	54,729	48,853
Stockholders' equity:
Additional paid-in capital	832	775
Retained earnings	251	203
Accumulated other comprehensive income, net of income taxes of $1 and $0 as of December 31, 2017 and 2016	9	(2)
Treasury stock, at cost, 133,294 and 134,439 shares as of December 31, 2017 and 2016	(3)	(3)
Total stockholders' equity	1,090	974
Noncontrolling interests	5,343	4,846
Total equity	6,433	5,820
Total liabilities and stockholders' equity	61,162	54,673
Common Class A
Stockholders' equity:
Common stock	1	1
Common Class B
Stockholders' equity:
Common stock

Consolidated Statements of Fin3

Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 40	$ 97
Accumulated Other Comprehensive Income, Tax	$ 1	$ 0
Treasury stock shares	133,294	134,439
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	71,609,049	68,119,412
Common stock, shares outstanding	71,475,755	67,984,973
Common Class B
Shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Trading gains	$ 40	$ 163	$ 269
Commissions	647	612	617
Interest income	908	606	492
Other income (loss)	332	94	(122)
Total revenues	1,927	1,475	1,256
Interest expense	225	79	67
Total net revenues	1,702	1,396	1,189
Non-interest expenses:
Execution and clearing	241	244	231
Employee compensation and benefits	249	242	227
Occupancy, depreciation and amortization	47	51	44
Communications	28	30	25
General and administrative	86	62	58
Customer bad debt	2	6	146
Total non-interest expenses	653	635	731
Income before income taxes	1,049	761	458
Income tax expense	256	62	43
Net income	793	699	415
Less net income attributable to noncontrolling interests	717	615	366
Net income available for common stockholders	$ 76	$ 84	$ 49
Earnings per share:
Basic	$ 1.09	$ 1.28	$ 0.80
Diluted	$ 1.07	$ 1.25	$ 0.78
Weighted average common shares outstanding:
Weighted Average Number of Shares Outstanding, Basic	69,926,933	66,013,247	61,043,071
Weighted Average Number of Shares Outstanding, Diluted	70,904,921	67,299,413	62,509,796
Comprehensive income:
Net income available for common stockholders	$ 76	$ 84	$ 49
Other comprehensive income:
Cumulative translation adjustment, before income taxes	11	(4)	(10)
Other comprehensive income (loss), net of tax	11	(4)	(10)
Comprehensive income available for common stockholders	87	80	39
Comprehensive income attributable to noncontrolling interests:
Net income attributable to noncontrolling interests	717	615	366
Other comprehensive income - cumulative translation adjustment	54	(21)	(53)
Comprehensive income attributable to noncontrolling interests	$ 771	$ 594	$ 313

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 793	$ 699	$ 415
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Deferred income taxes	147	27	15
Depreciation and amortization	25	25	22
Employee stock plan compensation	53	51	50
Unrealized (gain) loss on other investments, net	(4)	1	7
Gain on remeasurement of Tax Receivable Agreement liability	(93)
Bad debt expense	2	6	146
Impairment loss	21
Change in operating assets and liabilities:
Cash and securities - segregated for regulatory purposes	3,785	(2,708)	(5,905)
Securities borrowed	672	295	(264)
Securities purchased under agreements to resell	(1,924)	84	191
Financial instruments owned, at fair value	886	(647)	568
Receivables from customers	(10,414)	(2,365)	(144)
Other receivables	158	(342)	413
Other assets	(3)	3	13
Securities loaned	151	1,399	(305)
Securities sold under agreement to repurchase	1,316
Financial instruments sold but not yet purchased, at fair value	(1,378)	(454)	38
Payable to customers	5,817	4,647	5,288
Other payables	132	(177)	177
Net cash provided by operating activities	142	544	725
Cash flows from investing activities:
Purchases of other investments		(17)	(16)
Distributions received and proceeds from sales of other investments	2	38	11
Purchase of property and equipment	(28)	(27)	(30)
Net cash used in investing activities	(26)	(6)	(35)
Cash flows from financing activities:
Short-term borrowings, net	(59)	74	(34)
Dividends paid to stockholders	(28)	(26)	(25)
Distributions to noncontrolling interests	(272)	(219)	(227)
Repurchases of common stock for employee tax withholding under stock incentive plans	(21)	(26)	(25)
Proceeds from sales of treasury stock	21	25	29
Payments made under the Tax Receivable Agreement	(15)	(17)	(13)
Net cash used in financing activities	(374)	(189)	(295)
Effect of exchange rate changes on cash and cash equivalents	65	(25)	(63)
Net increase (decrease) in cash and cash equivalents	(193)	324	332
Cash and cash equivalents at beginning of period	1,925	1,601	1,269
Cash and cash equivalents at end of period	1,732	1,925	1,601
Supplemental disclosures of cash flow information:
Cash paid for interest	209	77	68
Cash paid for taxes, net	47	29	31
Non-cash financing activities:
Issuance of Common Stock in exchange of member interests in IBG LLC	49	56	132
Redemption of member interests from IBG Holdings LLC	(49)	(56)	(132)
Adjustments to additional paid-in capital for changes in proportionate ownership in IBG LLC	28	25	26
Adjustments to noncontrolling interests for changes in proportionate ownership in IBG LLC	$ (28)	(25)	$ (26)
Non-cash distribution to noncontrolling interests		$ (5)

Consolidated Statements of Chan

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
Issuance of common stock in follow-on offering		39				39	(39)
Number of new stock issued during the period (in shares)	3,021,778
Common Stock distributed pursuant to stock incentive plans (in shares)	2,487,127
Compensation for stock grants vesting in the future		9				9	41	50
Deferred tax benefit retained - follow-on offering		5				5		5
Repurchase of common stock for employee tax withholding under stock incentive plans			(25)			(25)		(25)
Sales of treasury stock		4	25			29		29
Dividends paid to stockholders				(25)		(25)		(25)
Distributions from IBG LLC to noncontrolling interests							(227)	(227)
Adjustments for changes in proportionate ownership in IBG LLC		26				26	(26)
Comprehensive Income				49	(10)	39	313	352
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
Issuance of common stock in follow-on offering		22				22	(22)
Number of new stock issued during the period (in shares)	1,596,200
Common Stock distributed pursuant to stock incentive plans (in shares)	2,402,062
Compensation for stock grants vesting in the future		8				8	43	51
Deferred tax benefit retained - follow-on offering		2				2		2
Repurchase of common stock for employee tax withholding under stock incentive plans			(26)			(26)		(26)
Sales of treasury stock			26			26	(1)	25
Dividends paid to stockholders				(26)		(26)		(26)
Distributions from IBG LLC to noncontrolling interests							(224)	(224)
Adjustments for changes in proportionate ownership in IBG LLC		25				25	(25)
Comprehensive Income				84	(4)	80	594	674
Balance at Dec. 31, 2016	$ 1	775	(3)	203	(2)	974	4,846	$ 5,820
Common stock, shares issued at Dec. 31, 2016	68,119,412
Issuance of common stock in follow-on offering		18				18	(18)
Number of new stock issued during the period (in shares)	1,214,860							1,214,860
Common Stock distributed pursuant to stock incentive plans (in shares)	2,274,777
Compensation for stock grants vesting in the future		9				9	44	$ 53
Deferred tax benefit retained - follow-on offering		2				2		2
Repurchase of common stock for employee tax withholding under stock incentive plans			(21)			(21)		(21)
Sales of treasury stock			21			21		21
Dividends paid to stockholders				(28)		(28)		(28)
Distributions from IBG LLC to noncontrolling interests							(272)	(272)
Adjustments for changes in proportionate ownership in IBG LLC		28				28	(28)
Comprehensive Income				76	11	87	771	858
Balance at Dec. 31, 2017	$ 1	$ 832	$ (3)	$ 251	$ 9	$ 1,090	$ 5,343	$ 6,433
Common stock, shares issued at Dec. 31, 2017	71,609,049

Organization Of Business

Organization Of Business	12 Months Ended
	Dec. 31, 2017
Organization Of Business [Abstract]
Organization Of Business	1. Organization of Business Interactive Brokers Group, Inc. (“IBG, Inc.”) is a Delaware holding company whose primary asset is its ownership of approximately 17.4% 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 120 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, the United Kingdom , Switzerland, Liechtenstein, India, China (Hong Kong and Shanghai), Japan, and Australia. As of December 31, 2017 , the Company had 1,228 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 (U.K.) Limited and its subsidiary, Interactive Brokers (U.K.) Nominee Limited (collectively, “IBUK”); Interactive Brokers (India) Private Limited (“IBI”); Timber Hill LLC (“TH LLC”); Timber Hill Australia Pty Limited (“THA”); Timber Hill Canada Company (“THC”); Interactive Brokers Financial Products S.A. (“IBFP”); Interactive Brokers Software Services (India) Private Limited (“IBSSI”); IB Exchange Corp. (“IBEC”) and its subsidiaries ; Interactive Brokers Canada Inc. (“IBC”); Interactive Brokers Securities Japan, Inc. (“IBSJ”); Interactive Brokers Hong Kong Limited (“IBHK”); 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 Europe AG and its subsidiary, Timber Hill (Liechtenstein) AG (collectively, “THE”) ; Interactive Brokers Hungary KFT (“IBH”); Interactive Brokers Software Services Estonia OU (“IBEST”); Interactive Brokers Software Services Russia (“IBRUS”); Interactive Brokers Corp. (“IB Corp”), Covestor, Inc. and its subsidiary, Covestor Limited (collectively, “Covestor”) , and Greenwich Advisor Compliance Services Corp . (“Greenwich Compliance”). 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 some of the world’s leading exchanges and market centers, primarily in exchange ‑traded equities, equity options and equity ‑index options and futures. (See Note 2 – Discontinued Operations and Costs Associated with Exit or Disposal Activities.) Corporate enables the Company to operate cohesively and effectively by providing support via development services and 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 14 ). IB LLC, IBC, IBUK, IBSJ, IBHK, IBI and IBA carry securities accounts for customers or perform custodial functions relating to customer securities. 

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Significant Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of Presentation These 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 ‑K. These 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. Principles of Consolidation, including Noncontrolling Interests  These 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. Discontinued Operations and Costs Associated with Exit or Disposal Activities On March 8, 2017, the Company announced its intention to discontinue its options market making activities globally. Additionally, as previously announced, on September 29, 2017 the Company completed the transfer of its U.S. options market making operations to Two Sigma Securities, LLC and a gain on sale of $11 million, reflecting the recovery of exit costs, was recorded in other income in the consolidated statements of comprehensive income. The Company will continue to phase out its options market making operations outside of the U.S. substantially over the coming months and expects to report discontinued operations when it meets the criteria under FASB Topic ASC 205-20, “Discontinued Operations.”  Consistent with earlier estimates, the Company recognized approximately $25 million in one-time restructuring costs during the year ended December 31, 2017. The one-time restructuring costs include approximately $22 million of non-cash expenditures, consisting of impairment of the carrying value of certain exchange trading rights and stock-based compensation, included in general and administrative expenses and employee compensation and benefits, respectively, and $3 million of cash expenditures primarily related to severance costs for employee terminations, included employee compensation and benefits, in the consolidated statements of comprehensive income. 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 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, costs associated with exit or disposal activities, 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 for similar assets in an active market, 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 since inputs to their valuation can be generally corroborated by market data. 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 in active markets 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 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 the plans’ post-employment 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 the plans’ post-employment provisions 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 be eligible to earn 50% of previously granted but not yet earned awards, unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of previously granted but not yet earned awards. 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 $4.5 billion and $7.4 billion as of December 31 , 2017 and December 31, 2016, respectively, and securities purchased under agreements to resell in the amount of $9.2 billion and $11.0 billion as of December 31 , 2017 and December 31, 2016, 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 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 consolidated statements of comprehensive income. Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase Securities purchased under agreements to resell and securities sold under agreements to repurchase, 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 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 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 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 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 consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $23 million as of December 31 , 2017 ( $ 2 2 million as of December 31, 2016), which are included in other assets in the 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, $11 million as of December 31 , 2017 ( $33 million as of December 31, 2016), 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 consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the 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 impairment 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 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. Upon retirement or disposition of property and equipment, the cost and related accumulated depreciation are removed from the consolidated statements of financial condition and any resulting gain or loss is recorded in other income in the consolidated statements of comprehensive income. Fully depreciated (or amortized) assets are retired on an annual basis. Comprehensive Income and Foreign Currency Translation The Company’s operating results are reported in the 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 on OCI. 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 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 consolidated statements of comprehensive income. Commissions Commissions earned for executing and/or clearing transactions are accrued on a trade date basis and are reported as commissions in the 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 consolidated statements of comprehensive income. Foreign Currency Gains and Losses Foreign currency balances are assets and liabilities in currencies other than the Company’s functional currency. At every reporting date, the Company revalues its foreign currency balances to its functional currency at the spot exchange rate and records the associated foreign currency gains and losses. These foreign currency gains and losses are reported in the consolidated statements of comprehensive income, as follows: (a) foreign currency gains and losses related to the Company’s currency diversification strategy are reported in other income; (b) foreign currency gains and losses related to the market making core-business activities are reported in trading gains; (c) foreign currency gains and losses arising from currency swap transactions in the electronic brokerage business are reported in interest income; and (d) all other foreign currency gains and losses are reported in other 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 and are recorded on an accrual basis. Rebates are recorded net within execution and clearing expenses in the 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 in the 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 the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates. Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of 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. On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was enacted, significantly revising the U.S corporate income tax law by, among other things, reducing the corporate income tax rate from 35% to 21% and implementing a modified territorial tax system that includes a one-time transition tax on deemed repatriated earnings of foreign subsidiaries (see Note 10). 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. The Company recognizes 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 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 consolidated statements of comprehensive income. 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 consolidated financial statements :     Affects Status   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 the recognition of a right-of-use asset and a lease liability for leases previously classified as operating leases in the statements of financial condition. Effective for fiscal years beginning after December 15, 2018.  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 2016-10 Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Effective for fiscal years beginning after December 15, 2019.  ASU 2016-15 Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. Effective for fiscal years beginning after December 15, 2017.  ASU 2016-16 Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2017-01 Business Combinations (Topic 805): Clarifying the Definition of a Business. Effective for annual periods beginning after December 15, 2017.  ASU 2017-04 Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. Effective for fiscal years beginning after December 15, 2019.  ASU 2017-05 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2017-08 Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Amending the amortization period for certain purchased callable debt securities held at a premium. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2017-09 Compensation—Stock Compensation (Topic 718): Providing clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Topic 718, Compensation—Stock Compensation, to a change to the terms or conditions of a share-based payment award. Effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017.  ASU 2017-11 Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), and Derivatives and Hedging (Topic 815): C hanging the classification analysis of certain equity-linked financial instruments (or embedded features) with down round features. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2017-12 Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  Adoption of those ASUs that became effective during 2017 and 2018, prior to the issuance of the Company’s consolidated financial statements, did not have a material effect on these financial statements.  The Company has reviewed the impact of FASB ASC Topic 606, “Revenue from Contracts with Customers” (“ASC Topic 606”), and identified similar performance obligations under ASC Topic 606 as compared with deliverables and separate units of account previously identified, as a result the Company expects the timing of its revenue recognition to remain the same as compared to FASB ASC Topic 605, “Revenue Recognition.” The Company adopted ASC Topic 606 using the modified retrospective method, effective January 1, 2018 .

Trading Activities And Related

Trading Activities And Related Risks	12 Months Ended
	Dec. 31, 2017
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 owned, at fair value and financial instruments sold, but not yet purchased, at fair value. 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 a currency diversification strategy that is based on a defined basket of 14 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 consolidated statements of comprehensive income. In light of the Company’s decision to discontinue its options market making activities globally, the Company removed the Singapore dollar (SGD) and realigned the relative weight of the U.S. dollar (USD) versus the other currency components to better reflect its businesses going forward. The new composition went into effect as of the close of business on March 31, 2017. 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, 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 December 31, 2017, 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 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 consolidated statements of financial condition.  

Equity And Earnings Per Share

Equity And Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Equity And Earnings Per Share [Abstract]
Equity And Earnings Per Share	4. Equity and Earnings p er 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 December 31 , 2017.    IBG, Inc. Holdings Total  Ownership % 17.4% 82.6% 100.0%  Membership interests 71,479,604 340,229,444 411,709,048  These 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 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 December 31 , 2017 and December 31, 2016 , 1,000,000,000 shares of Class A common stock were authorized, of which 71,609,049 and 68,119,412 shares have been issued; and 71,475,755 and 67,984,973 shares were outstanding, respectively. Class B common stock is comprised of 100 authorized shares, of which 100 shares were issued and outstanding as of December 31 , 2017 and December 31, 2016 , respectively. In addition, 10,000 shares of preferred stock have been authorized, of which no shares are issued or outstanding as of December 31 , 2017 and December 31, 2016 , 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 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 December 31 , 2017 and December 31, 2016 , the unamortized balance of these deferred tax assets was $146 million and $273 million, respectively (see Note 10 for effects of the Tax Act) . 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 consolidated statements of financial condition. The remaining 15% is accounted for as a permanent increase to additional paid ‑in capital in the Company’s consolidated statements of financial condition . As a result of the reduction of the corporate rate from 35% to 21% under the Tax Act, the Company remeasure d the Tax Receivable Agreement liability, payable to Holdings, resulting in the recognition of a $93 million gain which is reported in other income in the consolidated statements of comprehensive income. 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 December 31 , 2017 were $483 million, $410 million , and $73 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 $131 million through December 31 , 2017 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 2016, IBG, Inc. issued 12,643,495 shares of common stock (with a fair value of $362 million) directly to Holdings in exchange for an equivalent number of member interests in IBG LLC . On July 28, 2017, the Company filed a Supplemental Prospectus on Form 424B5 (File Number 333- 219552) with the SEC to issue 1,214,860 shares of common stock (with a fair value of $49 million) in exchange for an equivalent number of shares 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 17.4% , with Holdings owning the remaining 82.6% as of December 31 , 2017 . 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 89.2% as of December 31 , 2017 .  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.    Year-Ended December 31,  2017 2016 2015   (in millions, except share or per share amounts)  Basic earnings per share  Net income available for common stockholders $ 76 $ 84 $ 49  Weighted average shares of common stock outstanding  Class A 69,926,833 66,013,147 61,042,971  Class B 100 100 100  69,926,933 66,013,247 61,043,071  Basic earnings per share $ 1.09 $ 1.28 $ 0.80  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.     Year-Ended December 31,  2017 2016 2015  (in millions, except share or per share amounts)  Diluted earnings per share  Net income available for common stockholders $ 76 $ 84 $ 49  Weighted average shares of common stock outstanding  Class A  Issued and outstanding 69,926,833 66,013,147 61,042,971  Potentially dilutive common shares  Issuable pursuant to employee stock incentive plans 977,988 1,286,166 1,466,725  Class B 100 100 100  70,904,921 67,299,413 62,509,796  Diluted earnings per share $ 1.07 $ 1.25 $ 0.78  Member Distributions and Stockholder Dividends During the three years ended December 31 , 2017, 2016, and 2015 , IBG LLC made distributions totaling $328 million , $267 million, and $267 million , to its members, of which IBG, Inc. ’ s proportionate share was $56 million , $43 million, and $40 million, respectively . T he Company paid quarterly cash dividends of $0.10 per share of c ommon s tock, totaling $28 million, $26 million, and $25 million during 2017, 2016, and 2015, respectively . On January 16, 2018 , the Company declared a cash dividend of $0.10 per common share, payable on March 14, 2018 to stockholders of record as of March 1, 2018 .

Comprehensive Income

Comprehensive Income	12 Months Ended
	Dec. 31, 2017
Comprehensive Income Detail [Abstract]
Comprehensive Income	5. Comprehensive Income The following table presents comprehensive income and earnings per share on comprehensive income :      Year-Ended December 31,  2017 2016 2015  (in millions, except share or per share amounts)   Comprehensive income available for common stockholders $ 87 $ 80 $ 39   Earnings per share on comprehensive income  Basic $ 1.24 $ 1.21 $ 0.64  Diluted $ 1.22 $ 1.19 $ 0.62  Weighted average common shares outstanding  Basic 69,926,933 66,013,247 61,043,071  Diluted 70,904,921 67,299,413 62,509,796    

Financial Assets And Financial

Financial Assets And Financial Liabilities	12 Months Ended
	Dec. 31, 2017
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 December 31 , 2017 and December 31, 2016 . 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 December 31, 2017   Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 4,519 $ — $ — $ 4,519  Financial instruments owned, at fair value  Stocks 2,000 — 1 2,001  Options 1,052 — — 1,052  Warrants and discount certificates 5 — — 5  U.S. and foreign government securities 60 — — 60  Corporate and municipal bonds — 1 3 4  Currency forward contracts — 32 — 32  Total financial instruments owned, at fair value 3,117 33 4 3,154  Total financial assets at fair value $ 7,636 $ 33 $ 4 $ 7,673      Financial Liabilities At Fair Value as of December 31, 2017  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 302 $ — $ — $ 302  Options 464 — — 464  Currency forward contracts — 1 — 1  Total financial instruments sold, but not yet purchased, at fair value 766 1 — 767  Total financial liabilities at fair value $ 766 $ 1 $ — $ 767        Financial Assets At Fair Value as of December 31, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 7,398 $ — $ — $ 7,398  Financial instruments owned, at fair value  Stocks 1,821 — — 1,821  Options 1,804 — — 1,804  Warrants and discount certificates 43 — — 43  U.S. and foreign government securities 363 — — 363  Corporate and municipal bonds — 2 1 3  Currency forward contracts — 3 — 3  Total financial instruments owned, at fair value 4,031 5 1 4,037  Total financial assets at fair value $ 11,429 $ 5 $ 1 $ 11,435      Financial Liabilities At Fair Value as of December 31, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 839 $ — $ — $ 839  Options 1,286 — — 1,286  Warrants and discount certificates 1 — — 1  Currency forward contracts — 19 — 19  Total financial instruments sold, but not yet purchased, at fair value 2,126 19 — 2,145  Total financial liabilities at fair value $ 2,126 $ 19 $ — $ 2,145 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 years ended December 31, 2017 and 2016 , there were no transfers between levels for financial assets and liabilities, at fair value. Level 3 Financial Assets and Financial Liabilities  The Company’s Level 3 financial assets are comprised of delisted and illiquid securities reported within financial instruments owned, at fair value in the consolidated statements of financial condition. During the year ended December 31, 2017 financial assets included $1 million of Level 3 securities which were transferred from Level 1 as certain stocks were no longer tradable in active markets and were valued by the Company based on internal estimates . In addition, the Company purchased a $2 million convertible bond in a private placement, which is classified as Level 3. During the year ended December 31, 2016 financial assets included $1 million of Level 3 securities which were transferred from Level 2 as a result of a security becoming illiquid. 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 :     Year-Ended December 31,  2017 2016 2015  (in millions)  Equities $ 42 $ 155 $ 254  Fixed income — — 1  Foreign exchange (2) 8 14  Total trading gains, net $ 40 $ 163 $ 269  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 gain s (losses) 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 s represent 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 consolidated statements of financial condition. The following table excludes certain financial instruments such as equity investments and all non-financial assets and liabilities :       December 31, 2017  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,732 $ 1,732 $ 1,732 $ - $ -  Cash and securities segregated for regulatory purposes 15,713 15,713 6,547 9,166 -  Securities borrowed 2,957 2,957 - 2,957 -  Securities purchased under agreements to resell 2,035 2,035 - 2,035 -  Receivables from customer 29,821 29,821 - 29,821 -  Receivables from broker, dealers, and clearing organizations 823 823 - 823 -  Interest receivable 116 116 - 116 -  Other assets 6 6 - 6 -  Total financial assets, not measured at fair value $ 53,203 $ 53,203 $ 8,279 $ 44,924 $ -      Financial liabilities, not measured at fair value  Short-term borrowings $ 15 $ 15 $ - $ 15 $ -  Securities loaned 4,444 4,444 - 4,444 -  Securities sold under agreements to repurchase 1,316 1,316 - 1,316 -  Payables to customer 47,548 47,548 - 47,548 -  Payables to brokers, dealers and clearing organizations 283 283 - 283 -  Interest payable 22 22 - 22 -  Total financial liabilities, not measured at fair value $ 53,628 $ 53,628 $ - $ 53,628 $ -            December 31, 2016  Carrying Value Fair Value Level 1 Level 2 Level 3  (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,925 $ 1,925 $ 1,925 $ - $ -  Cash and securities segregated for regulatory purposes 16,619 16,619 5,624 10,995 -  Securities borrowed 3,629 3,629 - 3,629 -  Securities purchased under agreements to resell 111 111 - 111 -  Receivables from customer 19,409 19,409 - 19,409  Receivables from broker, dealers, and clearing organizations 1,040 1,040 - 1,040 -  Interest receivable 57 57 - 57 -  Other assets 28 32 - 32 -  Total financial assets, not measured at fair value $ 42,818 $ 42,822 $ 7,549 $ 35,273 $ -        Financial liabilities, not measured at fair value  Short-term borrowings $ 74 $ 74 $ - $ 74 $ -  Securities loaned 4,293 4,293 - 4,293 -  Payables to customer 41,731 41,731 - 41,731 -  Payables to brokers, dealers and clearing organizations 239 239 - 239 -  Interest payable 6 6 - 6 -  Total financial liabilities, not measured at fair value $ 46,343 $ 46,343 $ - $ 46,343 $ -   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 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 set forth the netting of financial assets and of financial liabilities as of December 31 , 2017 and December 31, 2016:     December 31, 2017  Gross Amounts Not Offset  Amounts Amounts Net Amounts in the  of Financial Offset in the Presented in the 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 $ 9,166 1 $ — $ 9,166 $ (9,166) $ —  Securities borrowed 2,957 — 2,957 (2,822) 135  Securities purchased under agreements to resell 2,035 — 2,035 (2,035) —  Financial Instruments owned, at fair value  Options 1,052 — 1,052 (451) 601  Warrants and discount certificates 5 — 5 — 5  Currency forward contracts 32 — 32 — 32  Total $ 15,247 $ — $ 15,247 $ (14,474) $ 773     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 4,444 $ — $ 4,444 $ (4,201) $ 243  Securities sold under agreements to repurchase 1,316 — 1,316 (1,316) —  Financial instruments sold, but not yet purchased, at fair value  Options 464 — 464 (451) 13  Warrants and discount certificates — — — — —  Currency forward contracts 1 — 1 — 1  Total $ 6,225 $ — $ 6,225 $ (5,968) $ 257      December 31, 2016  Gross Amounts Not Offset  Amounts Amounts Net Amounts in the  of Financial Offset in the Presented in the 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 $ 10,995 1 $ — $ 10,995 $ (10,995) $ —  Securities borrowed 3,629 — 3,629 (3,488) 141  Securities purchased under agreements to resell 111 — 111 (111) —  Financial Instruments owned, at fair value  Options 1,804 — 1,804 (1,230) 574  Warrants and discount certificates 43 — 43 (1) 42  Currency forward contracts 3 — 3 — 3  Total $ 16,585 $ — $ 16,585 $ (15,825) $ 760     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 4,293 $ — $ 4,293 $ (4,158) $ 135  Financial instruments sold, but not yet purchased, at fair value  Options 1,286 — 1,286 (1,230) 56  Warrants and discount certificates 1 — 1 (1) —  Currency forward contracts 19 — 19 — 19  Total $ 5,599 $ — $ 5,599 $ (5,389) $ 210  (1) As of December 31 , 2017 and December 31, 2016 , the Company had $9.2 billion and $ 11.0 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 consolidated statements of financial condition. (2) The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at December 31, 2017 and 2016 . Secured Financing Transactions – Maturities and Collateral Pledged  The following table s present gross obligations for securities loaned transactions by remaining contractual maturity and class of collateral pledged as of December 31, 2017 and December 31, 2016:      December 31, 2017  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities loaned  Stocks $ 4,389 $ - $ - $ - $ 4,389  Corporate bonds 55 - - - 55  Total securities loaned 4,444 - - - 4,444   Securities sold under agreements to repurchase  U.S. government securities 1,316 - - - 1,316  Total $ 5,760 $ - $ - $ - $ 5,760           December 31, 2016  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 4,269 $ - $ - $ - $ 4,269  Corporate bonds 24 - - - 24  Total $ 4,293 $ - $ - $ - $ 4,293  

Collateralized Transactions

Collateralized Transactions	12 Months Ended
	Dec. 31, 2017
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 typical 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 December 31 , 2017 and December 31, 2016 , approximately $29.8 billion and $19.4 billion, respectively, of customer margin loans were outstanding. The following table summarizes the amounts related to collateralized transactions as of December 31 , 2017 and December 31, 2016 :     December 31, 2017 December 31, 2016  Permitted Sold or Permitted Sold or  to Repledge Repledged to Repledge Repledged   (in millions)  Securities lending transactions $ 23,662 $ 3,041 $ 13,768 $ 3,621  Securities purchased under agreements to resell transactions (1) 11,231 11,231 11,117 11,117  Customer margin assets 30,236 9,013 17,773 7,172  $ 65,129 $ 23,285 $ 42,658 $ 21,910  (1) As of December 31 , 2017 , $9.2 billion or 82% (as of December 31, 2016 , $11.0 billion or 99% ) 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. In the normal course of business, the Company pledges qualified securities with clearing organizations to satisfy daily margin and clearing fund requirements. As of December 31, 2017 and December 31, 2016, 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 December 31, 2017 and December 31, 2016 are presented in the following table :      December 31, December 31,  2017 2016   (in millions)  Stocks $ 1,150 $ 1,574  U.S. and foreign government securities 54 359  $ 1,204 $ 1,933 

Other Income

Other Income	12 Months Ended
	Dec. 31, 2017
Other Income [Abstract]
Other Income	8 . Other Income The components of other income for the years ended December 31 , 2017, 2016, and 2015 were:     Year-Ended December 31,  2017 2016 2015  (in millions)  Market data fees $ 39 $ 35 $ 30  Account activity fees 20 18 16  Risk exposure fees 24 19 21  Payments for order flow 15 14 17  Gains (losses) on financial instruments, at fair value and other investments, net 1 35 (18)  Gains (losses) from currency diversification strategy, net 110 (40) (206)  Other, net 123 13 18  $ 332 $ 94 $ (122)  Market data fees are charged to customers for market data services they subscribe to and are largely offset by the related costs paid to obtain market data from third party vendors. Account activity fees are charged to customers that do not generate the minimum monthly commission. The fee is the difference between the minimum required commission and the actual commissions generated. Risk exposure fees are earned from a small minority of customer accounts carrying positions with market risk that exceeds defined thresholds. Payments for order flow are earned from various options exchanges based upon options trading volume originated by the Operating Companies. Gains (losses) on financial instruments, at fair value and other investments, net include (1) realized and unrealized gains and losses on financial instruments that (a) are held for purposes other than the Company’s market making activities, (b) are subject to restrictions, or (c) are accounted for under the equity method and (2) dividends on investments accounted for under cost method. Other, net includes a gain on the sale of the Company’s U.S. market making operations to Two Sigma Securities, LLC of $11 million, reflecting the recovery of exit costs, and a $93 million gain from the remeasurement of the Tax Receivable Agreement liability as a result of the Tax Act (see Note 4 and Note 10). 

Employee Incentive Plans

Employee Incentive Plans	12 Months Ended
	Dec. 31, 2017
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 of service. Included in employee compensation and benefits expenses in the consolidated statements of comprehensive income were $3 million of plan contributions for each of the three years ended December 31 , 2017, 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 December 31, 2017 , the Company has 3,849 shares of common stock remaining to be distributed to former employees under the ROI Unit Stock Plan. 2007 Stock Incentive Plan  In 2017, the Company amended the 2007 Stock Incentive Plan (the “Stock Incentive Plan”) to extend its term for a ten-year period through April 24, 2027, pending stockholders’ approval at the Company’s 2018 Annual Meeting. Under the Company’s Stock Incentive Plan, up to 30 million shares of the Company’s common stock may be issued to satisfy vested restricted stock units granted 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 in “Business – Our Organizational Structure” in Part I Item 1 of this A nnual Report on Form 10 - K , 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 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 stock units . Stock Incentive Plan awards are subject to issuance over time . All previously granted but not yet earned awards may be cancelled by the Company 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. Restricted stock units 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 24,263 restricted stock units have been granted to the external directors cumulatively since the plan’s inception . Stock Incentive Plan awards grant ed (excluding 21,009 shares issued pursuant to the ROI Unit Stock Plan described above) and the related fair values since the plan’s inception are presented in the table below:     Fair Value at  Date of Grant  Units ($ millions)  Prior periods (since inception) 20,888,468 $ 397  December 31, 2015 1,211,533 52  December 31, 2016 1,451,136 1 55  December 31, 2017 923,407 2 55  24,474,544 $ 559 (1) Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017. (2) Granted under the Company’s amended 2007 Stock Incentive Plan, pending stockholder approval at the Company’s 2018 Annual Meeting. 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 consolidated statements of comprehensive income was $53 million , $51 million, and $50 million for the years ended December 31 , 2017, 2016, and 2015 , respectively. Estimated future compensation costs for unvested awards, net of credits for cancelled awards , as of December 31 , 2017 are $38 million. The following summarizes the Stock Incentive Plan and ROI Unit Stock Plan activities from December 31, 2014 through December 31 , 2017 :     Intrinsic Value  of SIP Units  Stock which Vested ROI Unit  Incentive Plan and were Distributed Stock Plan  Units ($ millions) (1) Shares  Balance, December 31, 2014 10,376,800 9,614  Granted 1,211,533 —  Cancelled (163,221) —  Distributed (2,487,127) $ 86 (3,244)  Balance, December 31, 2015 8,937,985 6,370  Granted 1,451,136 (2) —  Cancelled (69,340) —  Distributed (2,402,062) $ 88 (1,376)  Balance, December 31, 2016 7,917,719 4,994  Granted 923,407 (3) —  Cancelled (115,711) —  Distributed (2,274,777) $ 81 (1,145)  Balance, December 31, 2017 6,450,638 3,849  (1) Intrinsic value of SIP unit s distributed represents the compensation value reported to the participants. (2) Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017. (3) Granted under the Company’s amended 2007 Stock Incentive Plan, pending stockholder approval at the Company’s 2018 Annual Meeting. Awards previously granted but not yet earned under the stock plans are subject to the plans’ post-employment provisions in the event a participant ceases employment with the Company . Through December 31 , 2017 , a total of 573,197 restricted stock units have been distributed under these post ‑employment provisions. These distributions are included in the table above.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Taxes [Abstract]
Income Taxes	10 . Income Taxes Income tax expense for the three years ended December 31 , 2017, 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 and the enactment of the Tax Act, as discussed below. These noncontrolling interests are subject to U.S. taxation as partnerships. Accordingly, the income attributable to these noncontrolling interests is reported in the 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 members. 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 accounting and income tax return purposes.  The Tax Act, as previously described, makes broad and complex changes to the U.S. tax code, including, but not limited to, (1) reducing the U.S. federal corporate tax rate to 21% , e f fective January 1, 2018; (2) requiring a one-time transition tax on certain undistributed earnings of foreign subsidiaries to be paid over eight years ; (3) generally eliminating U.S. federal income taxes on dividends from foreign subsidiaries; (4) requiring a current inclusion in U.S. federal taxable income of certain earnings of controlled foreign corporations; (5) eliminating the corporate alternative minimum tax (“AMT”) and changing how existing AMT credits can be realized; (6) creating the base erosion anti-abuse tax, a new minimum tax; (7) creating a new limitation on deductible interest expense; (8) changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017; (9) repealing the Section 199 manufacturing deduction; and (10) full expensing of qualified property for tax return purposes.  The SEC staff issued Staff Accounting Bulletin 118 (“ SAB 118 ”) , which provides guidance on accounting for the tax effects of the Tax Act. SAB 118 provides a measurement period that should not extend beyond one year from the enactment of the Tax Act for entities to complete the accounting under ASC Topic 740. In accordance with SAB 118, an entity must reflect the income tax effects of those aspects of the Tax Act for which the accounting under ASC Topic 740 is complete. To the extent that an entity’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, the entity must record a provisional estimate on its financial statements. However, i f an entity cannot determine a provisional estimate to be included on its financial statements, the entity should continue to apply ASC Topic 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act.  The Company’s accounting for the following elements of the Tax Act is incomplete. However, the Company has made reasonable estimates of certain effects and, therefore, recorded provisional adjustments as follows:  Reduction of U.S. federal corporate tax rate: The Tax Act reduces the corporate tax rate to 21% , effective January 1, 2018. For certain of the Company’s deferred tax assets and liabilities, the Company has recognized a provisional net decrease of $115 million with a corresponding adjustment to deferred income tax expense (or deferred tax benefit) for the year ended December 31, 2017. While the Company has made a reasonable estimate of the impact of the reduction in corporate rate, it may be affected by other analyses related to the Tax Act, including, but not limited to, the calculation of deemed repatriation of deferred foreign income and the state tax effect of adjustments made to federal temporary differences. The Company is still analyzing certain aspects of the Tax Act and refining its calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. In connection with the remeasurement of its deferred tax asset arising from the acquisition of interests in IBG LLC, the Company also remeasured the related Tax Receivable Agreement liability, payable to Holdings, resulting in the recognition of a $93 million gain which is reported in other income in the consolidated statements of comprehensive income (see Note 4). Deemed Repatriation Transition Tax : The Deemed Repatriation Transition Tax (“Transition Tax”) is a tax on previously untaxed accumulated and current earnings of certain foreign subsidiaries. To determine the amount of the Transition Tax, the Company must determine, in addition to other factors, the amount of post-1986 earnings of the relevant foreign subsidiaries, as well as the amount of non-U.S. income taxes paid on such earnings. The Company has made a reasonable estimate of the Transition Tax and recorded a provisional Transition Tax obligation of $62 million. This amount may change when the calculation of post-1986 foreign earnings and profits previously deferred from U.S. federal taxation and the amounts held in cash or other specified assets are finalized. The Company does not expect any significant changes, but it is continuing to gather additional information to more precisely compute the amount of the Transition Tax.  The Tax Act creates a new requirement that g lobal intangible low taxes income (“GILTI”) earned by controlled foreign corporations (“CFC”s) must be included currently in the gross income of the CFC’s U.S. shareholder. GILTI is the excess of the shareholder’s “net CFC-tested income” over the deemed tangible income return, which is currently defined as the excess of (1) 10 percent of the aggregate of the U.S shareholder’s pro rata share of the qualified business asset investment in each CFC with respect to which it is a U.S shareholder over (2) the amount of certain interest expense taken into account in the determination of net CFC-tested income.  Because of the complexity of the new GILTI tax rules, the Company is continuing to evaluate this provision of the Tax Act and the application of ASC Topic 740. Under U.S. GAAP, the Company is allowed to make an accounting policy election of either (1) treating taxes due on future U.S. inclusions in taxable income related to GILTI as a current-period expense when incurred (the “period cost method”) or (2) factoring such amounts into the Company’s measurement of its deferred taxes (the “deferred method”). The Company selected the deferred method. The Company’s calculation of the deferred balance with respect to the new GILTI tax rules will depend, in part, on analyzing its global income to determine whether it expects to have future U.S. inclusions in taxable income related to GILTI and, if so, what the impact is expected to be. Because whether the Company expects to have future U.S. inclusions in taxable income related to GILTI depends on, not only its current structure and estimated future results of global operations, but its intent and ability to modify its structure and/or its business, the Company is not yet able to reasonably estimate the effect of this provision of the Tax Act. Therefore, the Company has not made any adjustments related to potential GILTI tax in its financial statements.  For the three years ended December 31, 2017, 2016, and 2015, the provision for income taxes consisted of:    Year-Ended December 31,  2017 2016 2015   (in millions)  Current  Federal $ 76 (1) $ 1 $ 4  State and local 1 — —  Foreign 32 34 24  Total current 109 35 28  Deferred  Federal 148 (2) 30 14  State and local — — —  Foreign (1) (3) 1  Total deferred 147 27 15  $ 256 $ 62 $ 43  ________________________________  (1) Includes $62 million of Transition Tax under the Tax Act. (2) Includes the remeasurement of deferred tax assets and liabilities of $115 million due to the Tax Act. A reconciliation of the statutory U.S. Federal income tax rate of 35% to the Company’s effective tax rate for the three years ending December 31, 2017, 2016, and 2015 is set forth below:    Year-Ended December 31,  2017 2016 2015  U.S. Statutory Tax Rate 35.0% 35.0% 35.0%  Less: rate attributable to noncontrolling interests (26.5%) (28.2%) (28.2%)  State, local and foreign taxes, net of federal benefit 2.1% 1.3% 2.6%  Subtotal 10.6% 8.1% 9.4%  Effects of the Tax Act 13.7% 0.0% 0.0%  24.3% 8.1% 9.4%  Significant components of the Company’s deferred tax assets and liabilities, which are reported in other assets and in other liabilities and accrued expenses, respectively, in the consolidated statements of financial condition, as of December 31, 2017, 2016, and 2015 were as follows:    December 31,  2017 2016 2015   (in millions)  Deferred tax assets  Arising from the acquisition of interests in IBG LLC $ 146 $ 273 $ 288  Deferred compensation 4 6 5  Other 7 18 18  Total deferred tax assets 157 297 311  Deferred tax liabilities  Foreign, primarily THE 1 2 3  Other — 1 —  Total deferred tax liabilities 1 3 3  Net deferred tax assets $ 156 $ 294 $ 308  As of and for the years ended December 31 , 2017 and 2016 , 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 December 31, 2017, 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 2008. As of December 31 , 2017 , accumulated earnings held by non ‑U.S. subsidiaries totaled $1.1 billion ( as of December 31, 2016 $1.0 billion ). Of this amount, approximately $0.3 billion ( as of December 31, 2016 $0.3 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 $0.2 billion as of December 31 , 2017 and December 31, 2016 , 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.

Property, Equipment and Intangi

Property, Equipment and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Property, Equipment and Intangible Assets [Abstract]
Property, Equipment and Intangible Assets	11 . Property, Equipment and Intangible Assets  Property, equipment and intangible assets, which are included in other assets in the 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. As of December 31, 2017 and 2016 , property, equipment and intangible assets consisted of:     December 31,  2017 2016   (in millions)  Leasehold improvements $ 7 $ 6  Computer equipment 17 14  Office furniture and equipment 2 2  26 22  Less - accumulated depreciation and amortization (12) (9)  Property and equipment, net 14 13   Internally developed software 52 49  Intangible assets (acquired technology) 8 7  Less - accumulated amortization (31) (28)  Intangible assets, net 29 28  Total property, equipment, and intangible assets, net $ 43 $ 41  Depreciation and amortization of $25 million, $25 million, and $22 million, for the three years ended December 31, 2017 , 2016 , and 2015 , respectively, is included in occupancy, depreciation and amortization expenses in the consolidated statements of comprehensive income. Amortization expense related to intangible assets is expected to be approximately $16 million, $ 10 million, and $3 million, for years ended December 31, 2018 , 2019 , and 2020 , respectively.

Commitments, Contingencies And

Commitments, Contingencies And Guarantees	12 Months Ended
	Dec. 31, 2017
Commitments, Contingencies And Guarantees [Abstract]
Commitments, Contingencies And Guarantees	12 . 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 $116 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 December 31 , 2017 and 2016, 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”) filed a complaint in the U.S. District Court for the Northern District of Illinois, Eastern Division, against IBG, Inc., IBG LLC, Holdings, and IB LLC. Thereafter, Trading Technologies dismissed IBG, Inc. and Holdings from the case, leaving only IBG LLC and IB LLC as defendants (“Defendants”). The operative complaint, as amended, alleges that the Defendants have infringed and continue to infringe twelve U.S. patents held by Trading Technologies. Trading Technologies is seeking, among other things, unspecified damages and injunctive relief (“the Litigation”). The Defendants filed an answer to Trading Technologies’ amended complaint, as well as related counterclaims. The Defendants deny Trading Technologies’ claims, assert that the asserted patents are not infringed and are invalid, and assert several other defenses as well. Trading Technologies also filed patent infringement lawsuits against approximately a dozen other companies in the same court. The Litigation was consolidated with the other lawsuits filed by Trading Technologies.  The Defendants and/or certain codefendants filed petitions with the United States Patent and Trademark Office (“USPTO”) for Covered Business Method Review (“CBM Review”) on the asserted patents. The District Court granted the Defendants’ motion to stay the Litigation pending the CBM Reviews. The USPTO Patent Trial Appeal Board found ten of the twelve asserted patents to be not patentable and two patents to be patentable. The Defendants have filed app eals on the claims that were held to be patentable.  It is difficult to predict the outcome of the matter, however, the Company believes it has meritorious defenses to the allegations made in the complaint and intends to defend itself vigorously against them. However, litigation is inherently uncertain and there can be no guarantee that the Company will prevail or that the Litigation can be settled on favorable terms.  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.  On February 19, 2016, the Company filed a motion to dismiss the class action complaint. On September 28, 2016, the Court issued an order granting the Company’s motion to dismiss and dismissing the complaint in its entirety, and without providing plaintiff leave to amend. On October 5, 2016, the Court entered judgment in the Company’s favor. On October 12, 2016, plaintiff filed motions for leave to file an amended complaint and to vacate or amend judgment. On November 14, 2016, plaintiff also filed a motion to disqualify the district judge. The Company opposed all three motions. In memoranda of decision dated August 29, 2017 and September 5, 2017, the Court denied the motions. On September 28, 2017, plaintiff appealed the order of dismissal and subsequent judgment to the United States Court of Appeals for the Second Circuit. On January 9, 2018, the plaintiff filed his appellate brief. The opposition brief is currently due on April 10, 2018. We believe that the appeal, like the original complaint, lacks merit. Further, even if the Court’s dismissal were to be overturned on appeal, we do 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 continue 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.  Leases Operating Companies have non ‑cancelable operating leases covering office space. All but one of the office space leases are subject to escalation clauses based on specified costs incurred by the respective landlords and contain renewal elections. Rent expense calculated on a straight ‑line basis for the Company was $15 million, $16 million and $14 million for the three years ended December 31, 2017, 2016, and 2015, respectively, and is included in occupancy, depreciation and amortization expenses in the consolidated statements of comprehensive income. As of December 31, 2017, the Company’s minimum annual lease commitments totaled $ 154 million, as follows:     Year (in millions)  2018 $ 15  2019 10  2020 10  2021 10  2022 14  Thereafter 95  $ 154  Guarantees  Certain of the Operating Companies provide guarantees to securities and commodities 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 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 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	12 Months Ended
	Dec. 31, 2017
Segment And Geographic Information [Abstract]
Segment And Geographic Information	13. 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 trade execution and clearing services to customers worldwide. The Company conducts its remaining market making business (see Note 2 – Discontinued Operations and Costs Associated with Exit or Disposal Cost) principally through its Timber Hill subsidiaries on some of 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 the Company’s 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 years ended December 31 , 2017, 2016, and 2015 , and total assets as of December 31 , 2017, 2016, and 2015 :     Year-Ended December 31,  2017 2016 2015  (in millions)  Net revenues  Electronic brokerage $ 1,405 $ 1,239 $ 1,097  Market making 86 190 298  Corporate 211 (33) (206)  Total net revenues $ 1,702 $ 1,396 $ 1,189  Income before income taxes  Electronic brokerage $ 860 $ 756 $ 536  Market making (27) 44 130  Corporate 216 (39) (208)  Total income before income taxes $ 1,049 $ 761 $ 458      December 31,  2017 2016 2015   (in millions)  Segment assets  Electronic brokerage $ 58,787 $ 50,072 $ 44,421  Market making 8,469 11,765 10,825  Corporate (6,094) (7,164) (6,512)  Total assets $ 61,162 $ 54,673 $ 48,734  The Company operates its automated global business in the U.S. and international markets on more than 120 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 years ended December 31 , 2017, 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.      Year-Ended December 31,  2017 2016 2015  (in millions)  Net revenues  United States $ 1,393 $ 1,046 $ 832  International 309 350 357  Total net revenues $ 1,702 $ 1,396 $ 1,189  Income before income taxes  United States $ 947 $ 632 $ 294  International 102 129 164  Total income before income taxes $ 1,049 $ 761 $ 458  

Regulatory Requirements

Regulatory Requirements	12 Months Ended
	Dec. 31, 2017
Regulatory Requirements [Abstract]
Regulatory Requirements	 14 . Regulatory Requirements As of December 31 , 2017 , aggregate excess regulatory capital for all of the Operating Companies was $4.5 billion. IB LLC, TH LLC and IB Corp are subject to the Uniform Net Capital Rule (Rule 15c3 ‑1) under the Exchange Act, IB LLC is also subject to 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. IBA is subject to the Australian Securities 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 $ 3,548 $ 495 $ 3,053  TH LLC 279 1 278  THE 614 92 522  Other regulated operating companies 773 121 652  $ 5,214 $ 709 $ 4,505  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 December 31 , 2017 , all of the regulated Operating Companies were in compliance with their respective regulatory capital requirements.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	15 . Related Party Transactions Receivable from affiliate, reported in other assets in the 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 consolidated statements of financial condition as of December 31 , 2017 and December 31, 2016 were accounts receivable from directors, officers and their affiliates of $250 million and $ 78 million and payables of $648 million and $ 468 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	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	16 . Subsequent Events As required by FASB ASC Topic 855, “ Subsequent Events,” the Company has evaluated subsequent events for adjustment to or disclosure in its consolidated financial statements through the date the consolidated financial statements were issued. Except as disclosed in Note 4 and Note 12 , no other recordable or disclosable events occurred.  *****  

Schedule I_Condensed Financial

Schedule I—Condensed Financial Information of Registrant (Parent Company Only)	12 Months Ended
	Dec. 31, 2017
Schedule I—Condensed Financial Information of Registrant (Parent Company Only) [Abstract]
Schedule I—Condensed Financial Information of Registrant (Parent Company Only)	   INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF FINANCIAL CONDITION    December 31,  (in millions, except share amounts) 2017 2016  Assets  Cash and cash equivalents $ — $ —  Investments in subsidiaries, equity basis 1,122 964  Other assets 156 297  Total assets $ 1,278 $ 1,261  Liabilities and Equity  Liabilities:  Payable to affiliates $ 187 $ 285  Accrued expenses and other liabilities 1 2  188 287  Stockholders' equity:  Common stock, $0.01 par value per share:  Class A – Authorized - 1,000,000,000, Issued - 71,609,049 and 68,119,412 shares, Outstanding – 71,475,755 and 67,984,973 shares as of December 31, 2017 and 2016 1 1  Class B – Authorized, Issued and Outstanding – 100 shares as of December 31, 2017 and 2016 — —  Additional paid-in capital 832 775  Retained earnings 251 203  Accumulated other comprehensive income, net of income taxes of $1 and $0 as of December 31, 2017 and 2016 9 (2)  Treasury stock, at cost, 133,294 and 134,439 shares as of December 31, 2017 and 2016 (3) (3)  Total equity 1,090 974  Total liabilities and equity $ 1,278 $ 1,261  See accompanying notes to the condensed financial statements.      INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF COMPREHENSIVE INCOME    Year-Ended December 31,  (in millions) 2017 2016 2015  Income (loss) before income from subsidiaries $ 92 $ (1) $ —  Undistributed gains of subsidiaries, net 147 117 67  Income tax expense 163 32 18  Net income $ 76 $ 84 $ 49   Net income available for common stockholders $ 76 $ 84 $ 49  Cumulative translation adjustment, net of tax 11 (4) (10)  Comprehensive income available for common stockholders $ 87 $ 80 $ 39  See accompanying notes to the condensed financial statements.      INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF CASH FLOWS    Year-Ended December 31,  (in millions) 2017 2016 2015  Cash flows from operating activities  Net income $ 76 $ 84 $ 49  Adjustments to reconcile net income to net cash provided by operating activities  Undistributed gains of subsidiaries, net (147) (117) (67)  Deferred income taxes 149 30 13  Gain on remeasurement of Tax Receivable Agreement liability (93) — —  Changes in operating assets and liabilities (9) 9 9  Net cash (used in) provided by operating activities (24) 6 4  Cash flows provided by investing activities 56 42 40  Cash flows used in financing activities (43) (44) (34)  Effect of exchange rate changes on cash and cash equivalents 11 (5) (10)  Net increase (decrease) in cash and cash equivalents — (1) —  Cash and cash equivalents at beginning of period — 1 1  Cash and cash equivalents at end of period $ — $ — $ 1  Supplemental disclosures of cash flow information  Cash paid for interest $ — $ — $ —  Cash paid for taxes, net $ 13 $ (1) $ —   Non-cash investing activities:  Non-cash distributions from subsidiaries $ — $ 1 $ —  See accompanying notes to the condensed financial statements.  INTERACTIVE BROKERS GROUP, INC. (Parent Company Only)  NOTES TO CONDEN SED FINANCIAL STATEMENTS 1. Basis of Presentation The accompanying condensed financial statements (the “Parent Company Financial Statements”) of Interactive Brokers Group, Inc. (“IBG, Inc.”), a Delaware holding company, including the notes thereto, should be read in conjunction with the consolidated financial statements of IBG, Inc. and its subsidiaries (the “Company”) and the notes thereto. IBG, Inc.’s primary asset is its ownership interest in IBG LLC, 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 120 electronic exchanges and market centers around the world and offering custody, prime brokerage, securities and margin lending services to customers. The preparation of the Parent Company Financial Statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts and disclosures in the condensed financial statements and accompanying notes. Income Taxes Refer to Note 2 to the consolidated financial statements. 2. Related Party Transactions As of December 31, 2107, there were no receivables from affiliates. Dividends received from IBG LLC for the three years ended December 31, 2017, 2016, and 2015, were $56 million, $43 million, and $40 million, respectively. As of December 31, 2017 and 2016, respectively, payable to affiliates of $187 million and $285 million consisted primarily of amounts payable to Holdings under the Tax Receivable Agreement. 3. Stockholders’ Equity Refer to Note 4 to the consolidated financial statements. 4. Employee Incentive Plans Refer to Note 9 to the consolidated financial statements. 5. Commitments, Contingencies and Guarantees Refer to Note 12 to the consolidated financial statements. 6. Subsequent Events As required by FASB ASC Topic, “Subsequent Events,” IBG, Inc. has evaluated subsequent events for adjustment to or disclosure in its condensed financial statements through the date the condensed financial statements were issued. Except as disclosed in Note 4 and Note 12 to the consolidated financial statements , no other recordable or disclosable events occurred.

Significant Accounting Polici24

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These 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 ‑K. These 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.
Principles Of Consolidation, Including Noncontrolling Interests	Principles of Consolidation, including Noncontrolling Interests  These 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.
Discontinued Operations And Costs Associated With Exit Or Disposal Activities	Discontinued Operations and Costs Associated with Exit or Disposal Activities On March 8, 2017, the Company announced its intention to discontinue its options market making activities globally. Additionally, as previously announced, on September 29, 2017 the Company completed the transfer of its U.S. options market making operations to Two Sigma Securities, LLC and a gain on sale of $11 million, reflecting the recovery of exit costs, was recorded in other income in the consolidated statements of comprehensive income. The Company will continue to phase out its options market making operations outside of the U.S. substantially over the coming months and expects to report discontinued operations when it meets the criteria under FASB Topic ASC 205-20, “Discontinued Operations.”  Consistent with earlier estimates, the Company recognized approximately $25 million in one-time restructuring costs during the year ended December 31, 2017. The one-time restructuring costs include approximately $22 million of non-cash expenditures, consisting of impairment of the carrying value of certain exchange trading rights and stock-based compensation, included in general and administrative expenses and employee compensation and benefits, respectively, and $3 million of cash expenditures primarily related to severance costs for employee terminations, included employee compensation and benefits, in the consolidated statements of comprehensive income.
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 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, costs associated with exit or disposal activities, 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 for similar assets in an active market, 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 since inputs to their valuation can be generally corroborated by market data. 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 in active markets 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.
Stock-Based Compensation	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 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 the plans’ post-employment 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 the plans’ post-employment provisions 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 be eligible to earn 50% of previously granted but not yet earned awards, unless the employee is over the age of 59, in which case the employee would be eligible to receive 100% of previously granted but not yet earned awards.
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 $4.5 billion and $7.4 billion as of December 31 , 2017 and December 31, 2016, respectively, and securities purchased under agreements to resell in the amount of $9.2 billion and $11.0 billion as of December 31 , 2017 and December 31, 2016, 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 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 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 and securities sold under agreements to repurchase, 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 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, at Fair Value	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 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 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 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 consolidated statements of comprehensive income. The recorded amounts of the Company’s equity method investments, $23 million as of December 31 , 2017 ( $ 2 2 million as of December 31, 2016), which are included in other assets in the 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, $11 million as of December 31 , 2017 ( $33 million as of December 31, 2016), 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 consolidated statements of financial condition. Dividends received from cost basis investments are included in other income in the 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 impairment loss is recognized in the period the determination is made .
Property, Equipment, and Intangible Assets	Property, Equipment, and Intangible Assets Property, equipment, and intangible assets, which are included in other assets in the 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. Upon retirement or disposition of property and equipment, the cost and related accumulated depreciation are removed from the consolidated statements of financial condition and any resulting gain or loss is recorded in other income in the consolidated statements of comprehensive income. Fully depreciated (or amortized) assets are retired on an annual basis.
Comprehensive Income And Foreign Currency Translation	Comprehensive Income and Foreign Currency Translation The Company’s operating results are reported in the 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 on OCI. 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 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 consolidated statements of comprehensive income. Commissions Commissions earned for executing and/or clearing transactions are accrued on a trade date basis and are reported as commissions in the 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 consolidated statements of comprehensive income. Foreign Currency Gains and Losses Foreign currency balances are assets and liabilities in currencies other than the Company’s functional currency. At every reporting date, the Company revalues its foreign currency balances to its functional currency at the spot exchange rate and records the associated foreign currency gains and losses. These foreign currency gains and losses are reported in the consolidated statements of comprehensive income, as follows: (a) foreign currency gains and losses related to the Company’s currency diversification strategy are reported in other income; (b) foreign currency gains and losses related to the market making core-business activities are reported in trading gains; (c) foreign currency gains and losses arising from currency swap transactions in the electronic brokerage business are reported in interest income; and (d) all other foreign currency gains and losses are reported in other 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 and are recorded on an accrual basis. Rebates are recorded net within execution and clearing expenses in the 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 in the 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 the U.S. and numerous foreign jurisdictions. Determining income tax expense requires significant judgments and estimates. Deferred income tax assets and liabilities arise from temporary differences between the tax and financial statements recognition of 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. On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was enacted, significantly revising the U.S corporate income tax law by, among other things, reducing the corporate income tax rate from 35% to 21% and implementing a modified territorial tax system that includes a one-time transition tax on deemed repatriated earnings of foreign subsidiaries (see Note 10). 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. The Company recognizes 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 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 consolidated statements of comprehensive income.
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 consolidated financial statements :     Affects Status   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 the recognition of a right-of-use asset and a lease liability for leases previously classified as operating leases in the statements of financial condition. Effective for fiscal years beginning after December 15, 2018.  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 2016-10 Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Effective for fiscal years beginning after December 15, 2019.  ASU 2016-15 Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. Effective for fiscal years beginning after December 15, 2017.  ASU 2016-16 Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2017-01 Business Combinations (Topic 805): Clarifying the Definition of a Business. Effective for annual periods beginning after December 15, 2017.  ASU 2017-04 Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. Effective for fiscal years beginning after December 15, 2019.  ASU 2017-05 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. Effective for annual reporting periods beginning after December 15, 2017.  ASU 2017-08 Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Amending the amortization period for certain purchased callable debt securities held at a premium. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2017-09 Compensation—Stock Compensation (Topic 718): Providing clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Topic 718, Compensation—Stock Compensation, to a change to the terms or conditions of a share-based payment award. Effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017.  ASU 2017-11 Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), and Derivatives and Hedging (Topic 815): C hanging the classification analysis of certain equity-linked financial instruments (or embedded features) with down round features. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2017-12 Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  ASU 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. Effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018.  Adoption of those ASUs that became effective during 2017 and 2018, prior to the issuance of the Company’s consolidated financial statements, did not have a material effect on these financial statements.  The Company has reviewed the impact of FASB ASC Topic 606, “Revenue from Contracts with Customers” (“ASC Topic 606”), and identified similar performance obligations under ASC Topic 606 as compared with deliverables and separate units of account previously identified, as a result the Company expects the timing of its revenue recognition to remain the same as compared to FASB ASC Topic 605, “Revenue Recognition.” The Company adopted ASC Topic 606 using the modified retrospective method, effective January 1, 2018 .

Equity And Earnings Per Share (

Equity And Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Equity And Earnings Per Share [Abstract]
IBG LLC Ownership of Member Interests	  IBG, Inc. Holdings Total  Ownership % 17.4% 82.6% 100.0%  Membership interests 71,479,604 340,229,444 411,709,048 
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.    Year-Ended December 31,  2017 2016 2015   (in millions, except share or per share amounts)  Basic earnings per share  Net income available for common stockholders $ 76 $ 84 $ 49  Weighted average shares of common stock outstanding  Class A 69,926,833 66,013,147 61,042,971  Class B 100 100 100  69,926,933 66,013,247 61,043,071  Basic earnings per share $ 1.09 $ 1.28 $ 0.80  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.     Year-Ended December 31,  2017 2016 2015  (in millions, except share or per share amounts)  Diluted earnings per share  Net income available for common stockholders $ 76 $ 84 $ 49  Weighted average shares of common stock outstanding  Class A  Issued and outstanding 69,926,833 66,013,147 61,042,971  Potentially dilutive common shares  Issuable pursuant to employee stock incentive plans 977,988 1,286,166 1,466,725  Class B 100 100 100  70,904,921 67,299,413 62,509,796  Diluted earnings per share $ 1.07 $ 1.25 $ 0.78 

Comprehensive Income (Tables)

Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Comprehensive Income Detail [Abstract]
Comprehensive Income Table	    Year-Ended December 31,  2017 2016 2015  (in millions, except share or per share amounts)   Comprehensive income available for common stockholders $ 87 $ 80 $ 39   Earnings per share on comprehensive income  Basic $ 1.24 $ 1.21 $ 0.64  Diluted $ 1.22 $ 1.19 $ 0.62  Weighted average common shares outstanding  Basic 69,926,933 66,013,247 61,043,071  Diluted 70,904,921 67,299,413 62,509,796 

Financial Assets And Financia27

Financial Assets And Financial Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Financial Assets And Financial Liabilities [Abstract]
Fair Value Table	   Financial Assets At Fair Value as of December 31, 2017   Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 4,519 $ — $ — $ 4,519  Financial instruments owned, at fair value  Stocks 2,000 — 1 2,001  Options 1,052 — — 1,052  Warrants and discount certificates 5 — — 5  U.S. and foreign government securities 60 — — 60  Corporate and municipal bonds — 1 3 4  Currency forward contracts — 32 — 32  Total financial instruments owned, at fair value 3,117 33 4 3,154  Total financial assets at fair value $ 7,636 $ 33 $ 4 $ 7,673      Financial Liabilities At Fair Value as of December 31, 2017  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 302 $ — $ — $ 302  Options 464 — — 464  Currency forward contracts — 1 — 1  Total financial instruments sold, but not yet purchased, at fair value 766 1 — 767  Total financial liabilities at fair value $ 766 $ 1 $ — $ 767        Financial Assets At Fair Value as of December 31, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Securities segregated for regulatory purposes $ 7,398 $ — $ — $ 7,398  Financial instruments owned, at fair value  Stocks 1,821 — — 1,821  Options 1,804 — — 1,804  Warrants and discount certificates 43 — — 43  U.S. and foreign government securities 363 — — 363  Corporate and municipal bonds — 2 1 3  Currency forward contracts — 3 — 3  Total financial instruments owned, at fair value 4,031 5 1 4,037  Total financial assets at fair value $ 11,429 $ 5 $ 1 $ 11,435      Financial Liabilities At Fair Value as of December 31, 2016  Level 1 Level 2 Level 3 Total   (in millions)  Financial instruments sold, but not yet purchased, at fair value  Stocks $ 839 $ — $ — $ 839  Options 1,286 — — 1,286  Warrants and discount certificates 1 — — 1  Currency forward contracts — 19 — 19  Total financial instruments sold, but not yet purchased, at fair value 2,126 19 — 2,145  Total financial liabilities at fair value $ 2,126 $ 19 $ — $ 2,145 
Trading Gains From Market Making Transactions	   Year-Ended December 31,  2017 2016 2015  (in millions)  Equities $ 42 $ 155 $ 254  Fixed income — — 1  Foreign exchange (2) 8 14  Total trading gains, net $ 40 $ 163 $ 269 
Financial Assets and Liabilities Not Measured at Fair Value	    December 31, 2017  Carrying Value Fair Value Level 1 Level 2 Level 3   (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,732 $ 1,732 $ 1,732 $ - $ -  Cash and securities segregated for regulatory purposes 15,713 15,713 6,547 9,166 -  Securities borrowed 2,957 2,957 - 2,957 -  Securities purchased under agreements to resell 2,035 2,035 - 2,035 -  Receivables from customer 29,821 29,821 - 29,821 -  Receivables from broker, dealers, and clearing organizations 823 823 - 823 -  Interest receivable 116 116 - 116 -  Other assets 6 6 - 6 -  Total financial assets, not measured at fair value $ 53,203 $ 53,203 $ 8,279 $ 44,924 $ -      Financial liabilities, not measured at fair value  Short-term borrowings $ 15 $ 15 $ - $ 15 $ -  Securities loaned 4,444 4,444 - 4,444 -  Securities sold under agreements to repurchase 1,316 1,316 - 1,316 -  Payables to customer 47,548 47,548 - 47,548 -  Payables to brokers, dealers and clearing organizations 283 283 - 283 -  Interest payable 22 22 - 22 -  Total financial liabilities, not measured at fair value $ 53,628 $ 53,628 $ - $ 53,628 $ -            December 31, 2016  Carrying Value Fair Value Level 1 Level 2 Level 3  (in millions)  Financial assets, not measured at fair value  Cash and cash equivalents $ 1,925 $ 1,925 $ 1,925 $ - $ -  Cash and securities segregated for regulatory purposes 16,619 16,619 5,624 10,995 -  Securities borrowed 3,629 3,629 - 3,629 -  Securities purchased under agreements to resell 111 111 - 111 -  Receivables from customer 19,409 19,409 - 19,409  Receivables from broker, dealers, and clearing organizations 1,040 1,040 - 1,040 -  Interest receivable 57 57 - 57 -  Other assets 28 32 - 32 -  Total financial assets, not measured at fair value $ 42,818 $ 42,822 $ 7,549 $ 35,273 $ -        Financial liabilities, not measured at fair value  Short-term borrowings $ 74 $ 74 $ - $ 74 $ -  Securities loaned 4,293 4,293 - 4,293 -  Payables to customer 41,731 41,731 - 41,731 -  Payables to brokers, dealers and clearing organizations 239 239 - 239 -  Interest payable 6 6 - 6 -  Total financial liabilities, not measured at fair value $ 46,343 $ 46,343 $ - $ 46,343 $ -  
Offsetting Assets	      December 31, 2017  Gross Amounts Not Offset  Amounts Amounts Net Amounts in the  of Financial Offset in the Presented in the 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 $ 9,166 1 $ — $ 9,166 $ (9,166) $ —  Securities borrowed 2,957 — 2,957 (2,822) 135  Securities purchased under agreements to resell 2,035 — 2,035 (2,035) —  Financial Instruments owned, at fair value  Options 1,052 — 1,052 (451) 601  Warrants and discount certificates 5 — 5 — 5  Currency forward contracts 32 — 32 — 32  Total $ 15,247 $ — $ 15,247 $ (14,474) $ 773      December 31, 2016  Gross Amounts Not Offset  Amounts Amounts Net Amounts in the  of Financial Offset in the Presented in the 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 $ 10,995 1 $ — $ 10,995 $ (10,995) $ —  Securities borrowed 3,629 — 3,629 (3,488) 141  Securities purchased under agreements to resell 111 — 111 (111) —  Financial Instruments owned, at fair value  Options 1,804 — 1,804 (1,230) 574  Warrants and discount certificates 43 — 43 (1) 42  Currency forward contracts 3 — 3 — 3  Total $ 16,585 $ — $ 16,585 $ (15,825) $ 760     (1) As of December 31 , 2017 and December 31, 2016, the Company had $9.2 billion and $11.0 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 consolidated statements of financial condition. (2) The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at December 31, 2017 and 2016.
Offsetting Liabilities	     (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 4,444 $ — $ 4,444 $ (4,201) $ 243  Securities sold under agreements to repurchase 1,316 — 1,316 (1,316) —  Financial instruments sold, but not yet purchased, at fair value  Options 464 — 464 (451) 13  Warrants and discount certificates — — — — —  Currency forward contracts 1 — 1 — 1  Total $ 6,225 $ — $ 6,225 $ (5,968) $ 257        (in millions)  Offsetting of Financial Liabilities  Securities loaned $ 4,293 $ — $ 4,293 $ (4,158) $ 135  Financial instruments sold, but not yet purchased, at fair value  Options 1,286 — 1,286 (1,230) 56  Warrants and discount certificates 1 — 1 (1) —  Currency forward contracts 19 — 19 — 19  Total $ 5,599 $ — $ 5,599 $ (5,389) $ 210  (1) As of December 31 , 2017 and December 31, 2016, the Company had $9.2 billion and $11.0 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 consolidated statements of financial condition. (2) The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at December 31, 2017 and 2016.  
Schedule of Securities Financing Transactions	    December 31, 2017  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities loaned  Stocks $ 4,389 $ - $ - $ - $ 4,389  Corporate bonds 55 - - - 55  Total securities loaned 4,444 - - - 4,444   Securities sold under agreements to repurchase  U.S. government securities 1,316 - - - 1,316  Total $ 5,760 $ - $ - $ - $ 5,760           December 31, 2016  Remaining Contractual Maturity  Overnight Less than 30 – 90 Over 90  and Open 30 days days days Total   (in millions)  Securities Loaned  Stocks $ 4,269 $ - $ - $ - $ 4,269  Corporate bonds 24 - - - 24  Total $ 4,293 $ - $ - $ - $ 4,293 

Collateralized Transactions (Ta

Collateralized Transactions (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Collateralized Transactions [Abstract]
Amounts Related To Collateralized Transactions	   December 31, 2017 December 31, 2016  Permitted Sold or Permitted Sold or  to Repledge Repledged to Repledge Repledged   (in millions)  Securities lending transactions $ 23,662 $ 3,041 $ 13,768 $ 3,621  Securities purchased under agreements to resell transactions (1) 11,231 11,231 11,117 11,117  Customer margin assets 30,236 9,013 17,773 7,172  $ 65,129 $ 23,285 $ 42,658 $ 21,910  (1) As of December 31 , 2017 , $9.2 billion or 82% (as of December 31, 2016 , $11.0 billion or 99% ) 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.
Financial Instruments Owned and Pledged as Collateral (table)	   December 31, December 31,  2017 2016   (in millions)  Stocks $ 1,150 $ 1,574  U.S. and foreign government securities 54 359  $ 1,204 $ 1,933 

Other Income (Tables)

Other Income (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income [Abstract]
Schedule Of Components Of Other Income	   Year-Ended December 31,  2017 2016 2015  (in millions)  Market data fees $ 39 $ 35 $ 30  Account activity fees 20 18 16  Risk exposure fees 24 19 21  Payments for order flow 15 14 17  Gains (losses) on financial instruments, at fair value and other investments, net 1 35 (18)  Gains (losses) from currency diversification strategy, net 110 (40) (206)  Other, net 123 13 18  $ 332 $ 94 $ (122) 

Employee Incentive Plans (Table

Employee Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Employee Incentive Plans [Abstract]
Share Grants And Fair Value	   Fair Value at  Date of Grant  Units ($ millions)  Prior periods (since inception) 20,888,468 $ 397  December 31, 2015 1,211,533 52  December 31, 2016 1,451,136 1 55  December 31, 2017 923,407 2 55  24,474,544 $ 559 (1) Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017. (2) Granted under the Company’s amended 2007 Stock Incentive Plan, pending stockholder approval at the Company’s 2018 Annual Meeting.
2007 Stock Incentive Plan, ROI Summary	   Intrinsic Value  of SIP Units  Stock which Vested ROI Unit  Incentive Plan and were Distributed Stock Plan  Units ($ millions) (1) Shares  Balance, December 31, 2014 10,376,800 9,614  Granted 1,211,533 —  Cancelled (163,221) —  Distributed (2,487,127) $ 86 (3,244)  Balance, December 31, 2015 8,937,985 6,370  Granted 1,451,136 (2) —  Cancelled (69,340) —  Distributed (2,402,062) $ 88 (1,376)  Balance, December 31, 2016 7,917,719 4,994  Granted 923,407 (3) —  Cancelled (115,711) —  Distributed (2,274,777) $ 81 (1,145)  Balance, December 31, 2017 6,450,638 3,849  (1) Intrinsic value of SIP unit s distributed represents the compensation value reported to the participants. (2) Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017. (3) Granted under the Company’s amended 2007 Stock Incentive Plan, pending stockholder approval at the Company’s 2018 Annual Meeting.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Taxes [Abstract]
Schedule Of The Provision For Income Taxes	 Year-Ended December 31,  2017 2016 2015   (in millions)  Current  Federal $ 76 (1) $ 1 $ 4  State and local 1 — —  Foreign 32 34 24  Total current 109 35 28  Deferred  Federal 148 (2) 30 14  State and local — — —  Foreign (1) (3) 1  Total deferred 147 27 15  $ 256 $ 62 $ 43  ________________________________  (1) Includes $62 million of Transition Tax under the Tax Act. (2) Includes the remeasurement of deferred tax assets and liabilities of $115 million due to the Tax Act.
Reconciliation Of The Statutory U.S. Federal Income Tax Rate Of 35% To The Company’s Effective Tax Rate	  Year-Ended December 31,  2017 2016 2015  U.S. Statutory Tax Rate 35.0% 35.0% 35.0%  Less: rate attributable to noncontrolling interests (26.5%) (28.2%) (28.2%)  State, local and foreign taxes, net of federal benefit 2.1% 1.3% 2.6%  Subtotal 10.6% 8.1% 9.4%  Effects of the Tax Act 13.7% 0.0% 0.0%  24.3% 8.1% 9.4% 
Significant Components Of The Company’s Deferred Tax Assets (Liabilities)	  December 31,  2017 2016 2015   (in millions)  Deferred tax assets  Arising from the acquisition of interests in IBG LLC $ 146 $ 273 $ 288  Deferred compensation 4 6 5  Other 7 18 18  Total deferred tax assets 157 297 311  Deferred tax liabilities  Foreign, primarily THE 1 2 3  Other — 1 —  Total deferred tax liabilities 1 3 3  Net deferred tax assets $ 156 $ 294 $ 308 

Property, Equipment and Intan32

Property, Equipment and Intangible Assets(Tables)	12 Months Ended
	Dec. 31, 2017
Property, Equipment and Intangible Assets [Abstract]
Property, Equipment and Intangible Assets	  December 31,  2017 2016   (in millions)  Leasehold improvements $ 7 $ 6  Computer equipment 17 14  Office furniture and equipment 2 2  26 22  Less - accumulated depreciation and amortization (12) (9)  Property and equipment, net 14 13   Internally developed software 52 49  Intangible assets (acquired technology) 8 7  Less - accumulated amortization (31) (28)  Intangible assets, net 29 28  Total property, equipment, and intangible assets, net $ 43 $ 41 

Commitments, Contingencies An33

Commitments, Contingencies And Guarantees (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments, Contingencies And Guarantees [Abstract]
Minimum Annual Lease Commitments	   Year (in millions)  2018 $ 15  2019 10  2020 10  2021 10  2022 14  Thereafter 95  $ 154 

Segment And Geographic Inform34

Segment And Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment And Geographic Information [Abstract]
Segment Information	   Year-Ended December 31,  2017 2016 2015  (in millions)  Net revenues  Electronic brokerage $ 1,405 $ 1,239 $ 1,097  Market making 86 190 298  Corporate 211 (33) (206)  Total net revenues $ 1,702 $ 1,396 $ 1,189  Income before income taxes  Electronic brokerage $ 860 $ 756 $ 536  Market making (27) 44 130  Corporate 216 (39) (208)  Total income before income taxes $ 1,049 $ 761 $ 458      December 31,  2017 2016 2015   (in millions)  Segment assets  Electronic brokerage $ 58,787 $ 50,072 $ 44,421  Market making 8,469 11,765 10,825  Corporate (6,094) (7,164) (6,512)  Total assets $ 61,162 $ 54,673 $ 48,734 
Schedule Of Total Net Revenues And Income Before Income Taxes By Geographic Area	   Year-Ended December 31,  2017 2016 2015  (in millions)  Net revenues  United States $ 1,393 $ 1,046 $ 832  International 309 350 357  Total net revenues $ 1,702 $ 1,396 $ 1,189  Income before income taxes  United States $ 947 $ 632 $ 294  International 102 129 164  Total income before income taxes $ 1,049 $ 761 $ 458 

Regulatory Requirements (Tables

Regulatory Requirements (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Requirements [Abstract]
Summary Of Capital, Capital Requirements And Excess Capital	   Net Capital/  Eligible Equity Requirement Excess   (in millions)  IB LLC $ 3,548 $ 495 $ 3,053  TH LLC 279 1 278  THE 614 92 522  Other regulated operating companies 773 121 652  $ 5,214 $ 709 $ 4,505 

Schedule I_Condensed Financia36

Schedule I—Condensed Financial Information of Registrant (Parent Company Only) (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule I—Condensed Financial Information of Registrant (Parent Company Only) [Abstract]
Condensed Statements Of Financial Condition (Parent Company Only)	   INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF FINANCIAL CONDITION    December 31,  (in millions, except share amounts) 2017 2016  Assets  Cash and cash equivalents $ — $ —  Investments in subsidiaries, equity basis 1,122 964  Other assets 156 297  Total assets $ 1,278 $ 1,261  Liabilities and Equity  Liabilities:  Payable to affiliates $ 187 $ 285  Accrued expenses and other liabilities 1 2  188 287  Stockholders' equity:  Common stock, $0.01 par value per share:  Class A – Authorized - 1,000,000,000, Issued - 71,609,049 and 68,119,412 shares, Outstanding – 71,475,755 and 67,984,973 shares as of December 31, 2017 and 2016 1 1  Class B – Authorized, Issued and Outstanding – 100 shares as of December 31, 2017 and 2016 — —  Additional paid-in capital 832 775  Retained earnings 251 203  Accumulated other comprehensive income, net of income taxes of $1 and $0 as of December 31, 2017 and 2016 9 (2)  Treasury stock, at cost, 133,294 and 134,439 shares as of December 31, 2017 and 2016 (3) (3)  Total equity 1,090 974  Total liabilities and equity $ 1,278 $ 1,261 
Condensed Statements Of Comprehensive Income (Parent Company Only)	   INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF COMPREHENSIVE INCOME    Year-Ended December 31,  (in millions) 2017 2016 2015  Income (loss) before income from subsidiaries $ 92 $ (1) $ —  Undistributed gains of subsidiaries, net 147 117 67  Income tax expense 163 32 18  Net income $ 76 $ 84 $ 49   Net income available for common stockholders $ 76 $ 84 $ 49  Cumulative translation adjustment, net of tax 11 (4) (10)  Comprehensive income available for common stockholders $ 87 $ 80 $ 39 
Condensed Statements Of Cash Flows (Parent Company Only)	   INTERACTIVE BROKERS GROUP, INC.  (Parent Company Only)  CONDENSED STATEMENTS OF CASH FLOWS    Year-Ended December 31,  (in millions) 2017 2016 2015  Cash flows from operating activities  Net income $ 76 $ 84 $ 49  Adjustments to reconcile net income to net cash provided by operating activities  Undistributed gains of subsidiaries, net (147) (117) (67)  Deferred income taxes 149 30 13  Gain on remeasurement of Tax Receivable Agreement liability (93) — —  Changes in operating assets and liabilities (9) 9 9  Net cash (used in) provided by operating activities (24) 6 4  Cash flows provided by investing activities 56 42 40  Cash flows used in financing activities (43) (44) (34)  Effect of exchange rate changes on cash and cash equivalents 11 (5) (10)  Net increase (decrease) in cash and cash equivalents — (1) —  Cash and cash equivalents at beginning of period — 1 1  Cash and cash equivalents at end of period $ — $ — $ 1  Supplemental disclosures of cash flow information  Cash paid for interest $ — $ — $ —  Cash paid for taxes, net $ 13 $ (1) $ —   Non-cash investing activities:  Non-cash distributions from subsidiaries $ — $ 1 $ — 

Organization Of Business (Detai

Organization Of Business (Details)	12 Months Ended
	Dec. 31, 2017employeesegment	May 03, 2007
Number of employees | employee	1,228
Number of operating segments | segment	2
IBG LLC [Member]
IBG Inc. ownership % of IBG LLC	17.40%	10.00%

Significant Accounting Polici38

Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	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 cancelled post employment			50.00%
Over 59 percent of shares eligible			100.00%
U.S. Treasury Securities	$ 4,500	$ 7,400
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes	9,200	11,000
Equity method investments	23	22
Cost method investments	$ 11	$ 33
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.
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, before Income Tax	$ 11
Restructuring and Related Cost, Expected Cost	25
Supplemental unemployment benefits severance benefits	3
Restructuring settlement and impairment provisions	$ 22
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]
Intangible assets useful lives	3 years
Maximum [Member] | Finite-Lived Intangible Assets [Member]
Intangible assets 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 Share39

Equity And Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended			36 Months Ended	72 Months Ended	128 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010	Dec. 31, 2016	Dec. 31, 2017	May 03, 2007
Equity And Earnings Per Share [Line Items]
IBG Holdings ownership % of IBG LLC	82.60%					82.60%	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	10,000
Preferred stock shares issued	0	0			0	0
Preferred stock shares outstanding	0	0			0	0
Amortization period DTA (years)	15 years
Unamortized deferred tax asset arising from equity offerings	$ 146	$ 273			$ 273	$ 146
Percent of tax savings owed to IBG Holdings LLC	85.00%
Percentage of tax savings retained by IBG Inc.	15.00%
Gain on remeasurement of Tax Receivable Agreement liability	$ 93
Deferred tax asset from common stock offerings	483					483
Tax savings owed to IBG Holdings LLC	410					410
Tax savings retained by IBG Inc.	73					73
Tax savings paid to IBG Holdings LLC						131
Shares reserved for future issuance							360,000,000
Shares redeemed by IBG Holdings from IBG LLC				5,013,259
Cash Redemptions IBG Holdings				$ 114
Fair Value of Issued Shares in Exchange for Membership Interests	$ 49	362			$ 362	$ 49
Shares Issued	1,214,860				12,643,495
Thomas Peterffy and Affiliates Ownership	89.20%					89.20%	84.60%
Distribution from IBG LLC	$ 328	267	$ 267
Cash distribution to IBG, Inc.	$ 56	43	40
Dividend per share	$ 0.10
Dividends paid to common shareholders	$ 28	$ 26	$ 25
Declaration Date	Jan. 16, 2018
Payment Date	Mar. 14, 2018
Record Date	Mar. 1, 2018
IBG LLC [Member]
Equity And Earnings Per Share [Line Items]
IBG Inc. ownership % of IBG LLC	17.40%					17.40%	10.00%
Common Class A
Equity And Earnings Per Share [Line Items]
Common stock, par value	$ 0.01	$ 0.01			$ 0.01	$ 0.01
Shares authorized	1,000,000,000	1,000,000,000			1,000,000,000	1,000,000,000
Common stock, shares issued	71,609,049	68,119,412			68,119,412	71,609,049
Common stock, shares outstanding	71,475,755	67,984,973			67,984,973	71,475,755
Common Class B
Equity And Earnings Per Share [Line Items]
Shares authorized	100	100			100	100
Common stock, shares issued	100	100			100	100
Common stock, shares outstanding	100	100			100	100

Equity And Earnings Per Share40

Equity And Earnings Per Share (IBG LLC Ownership of Member Interests) (Details)	Dec. 31, 2017shares
Ownership Percentage	100.00%
Membership Interests	411,709,048
IBG Inc [Member]
Ownership Percentage	17.40%
Membership Interests	71,479,604
Holdings [Member]
Ownership Percentage	82.60%
Membership Interests	340,229,444

Equity And Earnings Per Share41

Equity And Earnings Per Share (Basic Table) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic earnings per share:
Net income available for common stockholders	$ 76	$ 84	$ 49
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	69,926,933	66,013,247	61,043,071
Basic earnings per share	$ 1.09	$ 1.28	$ 0.80
Common Class A
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	69,926,833	66,013,147	61,042,971
Common Class B
Weighted average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	100	100	100

Equity And Earnings Per Share42

Equity And Earnings Per Share (Diluted Table) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Diluted earnings per share:
Net income available for common stockholders	$ 76	$ 84	$ 49
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	69,926,933	66,013,247	61,043,071
Potentially dilutive common shares:
Issuable pursuant to employee incentive plans	977,988	1,286,166	1,466,725
Weighted Average Number of Shares Outstanding, Diluted	70,904,921	67,299,413	62,509,796
Earnings Per Share, Diluted	$ 1.07	$ 1.25	$ 0.78
Common Class A
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	69,926,833	66,013,147	61,042,971
Common Class B
Weighted Average Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic	100	100	100

Comprehensive Income (Details)

Comprehensive Income (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Comprehensive Income Detail [Abstract]
Comprehensive income available for common stockholders	$ 87	$ 80	$ 39
Earnings per share on comprehensive income:
Basic	$ 1.24	$ 1.21	$ 0.64
Diluted	$ 1.22	$ 1.19	$ 0.62
Weighted average common shares outstanding:
Weighted Average Number of Shares Outstanding, Basic	69,926,933	66,013,247	61,043,071
Weighted Average Number of Shares Outstanding, Diluted	70,904,921	67,299,413	62,509,796

Financial Assets And Financia44

Financial Assets And Financial Liabilities (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers of financial instruments owned from level 1 to level 3	$ 1
Securities purchased under agreement to resell segregated for regulatory purposes	9,200	$ 11,000
Fair Value Assets Level 2 To Level 3 Amount		1
Total financial instruments owned, at fair value	3,154	4,037
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	4	$ 1
Level 3 | Convertible Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	$ 2

Financial Assets And Financia45

Financial Assets And Financial Liabilities (Fair Value Table) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities segregated for regulatory purposes	$ 4,519	$ 7,398
Total financial instruments owned, at fair value	3,154	4,037
Total Financial Assets at Fair Value	7,673	11,435
Financial instruments sold, not yet purchased, at fair value	767	2,145
Total Financial Liabilities at Fair Value	767	2,145
Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	2,001	1,821
Financial instruments sold, not yet purchased, at fair value	302	839
Options owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1,052	1,804
Financial instruments sold, not yet purchased, at fair value	464	1,286
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	5	43
Financial instruments sold, not yet purchased, at fair value		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	60	363
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	4	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	32	3
Financial instruments sold, not yet purchased, at fair value	1	19
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities segregated for regulatory purposes	4,519	7,398
Total financial instruments owned, at fair value	3,117	4,031
Total Financial Assets at Fair Value	7,636	11,429
Financial instruments sold, not yet purchased, at fair value	766	2,126
Total Financial Liabilities at Fair Value	766	2,126
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	2,000	1,821
Financial instruments sold, not yet purchased, at fair value	302	839
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	1,052	1,804
Financial instruments sold, not yet purchased, at fair value	464	1,286
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	5	43
Financial instruments sold, not yet purchased, at fair value		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	60	363
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	33	5
Total Financial Assets at Fair Value	33	5
Financial instruments sold, not yet purchased, at fair value	1	19
Total Financial Liabilities at Fair Value	1	19
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	1	2
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	32	3
Financial instruments sold, not yet purchased, at fair value	1	19
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	4	1
Total Financial Assets at Fair Value	4	1
Level 3 | Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial instruments owned, at fair value	1
Level 3 | 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	$ 1

Financial Assets And Financia46

Financial Assets And Financial Liabilities (Trading Gains from Market Making Transactions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financial Assets And Financial Liabilities [Abstract]
Equities	$ 42	$ 155	$ 254
Fixed Income			1
Foreign exchange	(2)	8	14
Total trading gains, net	$ 40	$ 163	$ 269

Financial Assets And Financia47

Financial Assets And Financial Liabilities (Financial Assets and Liabilities Not Measured at Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and cash equivalents	$ 1,732	$ 1,925	$ 1,601	$ 1,269
Cash and securities segregated for regulatory purposes	20,232	24,017
Securities borrowed	2,957	3,629
Securities purchased under agreements to resell	2,035	111
Receivables from customer	29,821	19,409
Receivables from brokers, dealers and clearing organizations	823	1,040
Interest receivable	116	57
Other assets	292	448
Short-term borrowings	15	74
Securities loaned	4,444	4,293
Securities sold under agreements to repurchase	1,316
Payables to customers	47,548	41,731
Payables to brokers, dealers and clearing organizations	283	239
Interest payable	22	6
at Fair Value
Cash and cash equivalents	1,732	1,925
Cash and securities segregated for regulatory purposes	15,713	16,619
Securities borrowed	2,957	3,629
Securities purchased under agreements to resell	2,035	111
Receivables from customer	29,821	19,409
Receivables from brokers, dealers and clearing organizations	823	1,040
Interest receivable	116	57
Other assets	6	32
Total financial assets, not measured at fair value	53,203	42,822
Short-term borrowings	15	74
Securities loaned	4,444	4,293
Securities sold under agreements to repurchase	1,316
Payables to customers	47,548	41,731
Payables to brokers, dealers and clearing organizations	283	239
Interest payable	22	6
Total financial liabilities, not measured at fair value	53,628	46,343
Carrying Value
Cash and cash equivalents	1,732	1,925
Cash and securities segregated for regulatory purposes	15,713	16,619
Securities borrowed	2,957	3,629
Securities purchased under agreements to resell	2,035	111
Receivables from customer	29,821	19,409
Receivables from brokers, dealers and clearing organizations	823	1,040
Interest receivable	116	57
Other assets	6	28
Total financial assets, not measured at fair value	53,203	42,818
Short-term borrowings	15	74
Securities loaned	4,444	4,293
Securities sold under agreements to repurchase	1,316
Payables to customers	47,548	41,731
Payables to brokers, dealers and clearing organizations	283	239
Interest payable	22	6
Total financial liabilities, not measured at fair value	53,628	46,343
Level 1
Cash and cash equivalents	1,732	1,925
Cash and securities segregated for regulatory purposes	6,547	5,624
Total financial assets, not measured at fair value	8,279	7,549
Short-term borrowings
Securities loaned
Securities sold under agreements to repurchase
Payables to customers
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	9,166	10,995
Securities borrowed	2,957	3,629
Securities purchased under agreements to resell	2,035	111
Receivables from customer	29,821	19,409
Receivables from brokers, dealers and clearing organizations	823	1,040
Interest receivable	116	57
Other assets	6	32
Total financial assets, not measured at fair value	44,924	35,273
Short-term borrowings	15	74
Securities loaned	4,444	4,293
Securities sold under agreements to repurchase	1,316
Payables to customers	47,548	41,731
Payables to brokers, dealers and clearing organizations	283	239
Interest payable	22	6
Total financial liabilities, not measured at fair value	53,628	46,343
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
Securities sold under agreements to repurchase
Payables to customers
Payables to brokers, dealers and clearing organizations
Interest payable
Total financial liabilities, not measured at fair value

Financial Assets And Financia48

Financial Assets And Financial Liabilities (Netting of Financial Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Securities, Segregated For Regulatory Purposes, Purchased Under Agreements To Resell [Abstract]
Gross Amounts of Financial Assets Recognized	[1]	$ 9,166	$ 10,995
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		9,166	10,995
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments		(9,166)	(10,995)
Net Amount
Offsetting Securities Borrowed [Abstract]
Gross Amounts of Financial Assets Recognized		2,957	3,629
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		2,957	3,629
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments		(2,822)	(3,488)
Net Amount		135	141
Offsetting Securities Purchased under Agreements to Resell [Abstract]
Gross Amounts of Financial Assets Recognized		2,035	111
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		2,035	111
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments		(2,035)	(111)
Net Amount
Total [Abstract]
Gross Amounts of Financial Assets Recognized		15,247	16,585
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		15,247	16,585
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments		(14,474)	(15,825)
Net Amount		773	760
Options [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		1,052	1,804
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		1,052	1,804
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments		(451)	(1,230)
Net Amount		601	574
Warrants And Discount Certificates [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		5	43
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		5	43
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments			(1)
Net Amount		5	42
Currency Forward Contracts [Member]
Offsetting Financial Instruments Owned, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		32	3
Amounts Offset in the Consolidated Statement of Financial Condition	[2]
Net Amounts Presented in the Consolidated Statement of Financial Condition		32	3
Amounts Not Offset in the Consolidated Statement of Financial Condition: Cash or Financial Instruments
Net Amount		$ 32	$ 3
[1]	As of December 31, 2017 and December 31, 2016, the Company had $9.2 billion and $11.0 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 consolidated statements of financial condition.
[2]	The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at December 31, 2017 and 2016.

Financial Assets And Financia49

Financial Assets And Financial Liabilities (Netting of Financial Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Offsetting Securities Loaned [Abstract]
Gross Amounts of Financial Assets Recognized		$ 4,444	$ 4,293
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition		4,444	4,293
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)		(4,201)	(4,158)
Net Amount		243	135
Securities Sold under Agreements to Repurchase [Abstract]
Gross Amounts of Financial Assets Recognized		1,316
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition		1,316
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)		(1,316)
Net Amount
Total [Abstract]
Gross Amounts of Financial Assets Recognized		6,225	5,599
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition		6,225	5,599
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)		(5,968)	(5,389)
Net Amount		257	210
Options [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		464	1,286
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition		464	1,286
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)		(451)	(1,230)
Net Amount		13	56
Warrants And Discount Certificates [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized			1
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition			1
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)			(1)
Net Amount
Currency Forward Contracts [Member]
Offsetting Financial Instruments Sold, But Not Yet Purchased, At Fair Value [Abstract]
Gross Amounts of Financial Assets Recognized		1	19
Amounts Offset in the Consolidated Statement of Financial Condition	[1]
Net Amounts Presented in the Consolidated Statement of Financial Condition		1	19
Amounts of Liabilities Not Offset in the Consolidated Statement of Financial Condition (Cash or Financial Instruments)
Net Amount		$ 1	$ 19
[1]	The Company did not have any balances eligible for netting in accordance with ASC Topic 210-20 at December 31, 2017 and 2016.

Financial Assets And Financia50

Financial Assets And Financial Liabilities (Secured Financing Transactions) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	$ 4,444	$ 4,293
Securities sold under agreements to repurchase	1,316
Total	5,760
US Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold under agreements to repurchase	1,316
Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	4,444	4,293
Total	5,760
Overnight and Open [Member] | US Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold under agreements to repurchase	1,316
Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	4,389	4,269
Common Stock [Member] | Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	4,389	4,269
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	55	24
Corporate Bonds [Member] | Overnight and Open [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities loaned	$ 55	$ 24

Collateralized Transactions (Na

Collateralized Transactions (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure Collateralized Transactions [Abstract]
Customers, less allowance for doubtful accounts of $40 and $97 as of December 31, 2017 and 2016	$ 29,821	$ 19,409
Securities purchased under agreement to resell segregated for regulatory purposes	$ 9,200	$ 11,000
Percentage of securities repledged and deposited for customers	82.00%	99.00%

Collateralized Transactions (Am

Collateralized Transactions (Amounts Related to Collateralized Transactions) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Permitted To Repledge [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		$ 23,662	$ 13,768
Agreements to resell	[1]	11,231	11,117
Customer margin assets		30,236	17,773
Total collateralized transactions		65,129	42,658
Sold Or Repledged [Member]
Collateralized Transactions [Line Items]
Securities lending transactions		3,041	3,621
Agreements to resell	[1]	11,231	11,117
Customer margin assets		9,013	7,172
Total collateralized transactions		$ 23,285	$ 21,910
[1]	As of December 31, 2017, $9.2 billion or 82% (as of December 31, 2016, $11.0 billion or 99%) 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	Dec. 31, 2017	Dec. 31, 2016
Disclosure Collateralized Transactions [Abstract]
Stocks	$ 1,150	$ 1,574
U.S. and foreign government securities	54	359
Financial Instruments Owned and Pledged as Collateral - Eligible to be Repledged by Counterparty	$ 1,204	$ 1,933

Other Income (Narrative) (Detai

Other Income (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Other Income [Abstract]
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, before Income Tax	$ 11
Gain on remeasurement of Tax Receivable Agreement liability	$ 93

Other Income (Schedule Of Compo

Other Income (Schedule Of Components Of Other Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income [Abstract]
Market data fees	$ 39	$ 35	$ 30
Account activity fees	20	18	16
Risk exposure fees	24	19	21
Payments for order flow	15	14	17
Gains (losses) on financial instruments, at fair value and other investments, net	1	35	(18)
Gains (losses) from currency diversification strategy, net	110	(40)	(206)
Other, net	123	13	18
Other income	$ 332	$ 94	$ (122)

Employee Incentive Plans (Narra

Employee Incentive Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended			128 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	May 03, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
401(k) plan contribution expense	$ 3	$ 3	$ 3
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	3,849
Maximum shares of stock distributable under 2007 Stock Incentive Plan	30,000,000			30,000,000
Shares granted to external directors				24,263
Stock Incentive Plan Granted Shares Adjustment		5,657
2007 Stock Incentive Plan Compensation Expense	$ 53	$ 51	$ 50
Estimated Future 2007 Stock Incentive Plan Compensation Expense	$ 38			$ 38
Post employment shares distribution				573,197
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				92 Months Ended	128 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2017
Employee Incentive Plans [Abstract]
Shares granted	923,407	1,451,136	[1]	1,211,533	20,888,468
Fair Value - Date of Grant	$ 55	$ 55		$ 52	$ 397	$ 55
Shares Granted IPO to Date						24,474,544
Fair Value - Date of Grant IPO to Date						$ 559
[1]	Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017.Granted under the Company's amended 2007 Stock Incentive Plan, pending stockholder approval at the Company's 2018 Annual Meeting.

Employee Incentive Plans (2007

Employee Incentive Plans (2007 Stock Incentive Plan, ROI Summary) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
2007 Stock Incentive Plan (Shares)
Beginning Balance		7,917,719		8,937,985		10,376,800
Shares Granted		923,407	[1]	1,451,136	[2]	1,211,533
Shares Cancelled		(115,711)		(69,340)		(163,221)
Shares Distributed		(2,274,777)		(2,402,062)		(2,487,127)
Ending Balance		6,450,638		7,917,719		8,937,985
Intrinsic Value Of SIP Shares Which Vested And Were Distributed [Member]
Distributed	[3]	$ 81		$ 88		$ 86
2007 ROI Unit Stock Plan (Shares) [Member]
Beginning Balance		4,994		6,370		9,614
Shares Distributed		(1,145)		(1,376)		(3,244)
Ending Balance		3,849		4,994		6,370
[1]	Granted under the Company's amended 2007 Stock Incentive Plan, pending stockholder approval at the Company's 2018 Annual Meeting.
[2]	Stock Incentive Plan number of granted restricted stock units related to 2016 was adjusted by 5,657 additional restricted stock units during the year ended December 31, 2017.
[3]	Intrinsic value of SIP units distributed represents the compensation value reported to the participants.

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S. Statutory Tax Rate		35.00%	35.00%	35.00%
Adjustment to deferred income tax expense (or deferred tax benefit)		$ 115
Provisional Transition Tax obligation		62
Gain on remeasurement of Tax Receivable Agreement liability		93
Undistributed accumulated earnings of foreign subsidiaries		1,100	$ 1,000
Accumulated earnings of foreign pass through subsidiaries		300	300
Accumulated earnings subject to additional foreign tax		$ 200	$ 200
Scenario, Plan [Member]
U.S. Statutory Tax Rate	21.00%

Income Taxes (Schedule Of The P

Income Taxes (Schedule Of The Provision For Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 76	[1]	$ 1	$ 4
State and local	1
Foreign	32		34	24
Total current	109		35	28
Deferred:
Federal	148	[2]	30	14
Foreign	(1)		(3)	1
Total deferred	147		27	15
Income tax expense	$ 256		$ 62	$ 43
[1]	Includes $62 million of Transition Tax under the Tax Act.
[2]	Includes the remeasurement of deferred tax assets and liabilities of $115 million due to the Tax Act.

Income Taxes (Reconciliation Of

Income Taxes (Reconciliation Of The Statutory U.S. Federal Income Tax Rate Of 35% To The Company’s Effective Tax Rate) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
U.S. Statutory Tax Rate	35.00%	35.00%	35.00%
Less: rate attributable to noncontrolling interests	(26.50%)	(28.20%)	(28.20%)
State, local and foreign taxes, net of federal benefit	2.10%	1.30%	2.60%
Subtotal	10.60%	8.10%	9.40%
Effects of the Tax Act	13.70%	0.00%	0.00%
Effective income tax rate	24.30%	8.10%	9.40%

Income Taxes (Significant Compo

Income Taxes (Significant Components Of The Company’s Deferred Tax Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Deferred tax asset arising from the acquisition of interests in IBGLLC	$ 146	$ 273	$ 288
Deferred compensation	4	6	5
Other	7	18	18
Total deferred tax assets	157	297	311
Deferred tax liabilities:
Foreign, primarily THE	1	2	3
Other		1
Total deferred tax liabilities	1	3	3
Net deferred tax assets	$ 156	$ 294	$ 308

Property, Equipment and Intan63

Property, Equipment and Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Equipment and Intangible Assets [Abstract]
Depreciation and amortization				$ 25	$ 25	$ 22
Amortization of Intangible Assets	$ 3	$ 10	$ 16

Property, Equipment and Intan64

Property, Equipment and Intangible Assets (Property And Equipment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Equipment and Intangible Assets [Abstract]
Leasehold improvements	$ 7	$ 6
Computer equipment	17	14
Office furniture and equipment	2	2
Property and equipment, gross	26	22
Less—accumulated depreciation and amortization	(12)	(9)
Property and equipment, net	14	13
Internally developed software	52	49
Intangible assets (acquired technology)	8	7
Less-accumulated amortization	(31)	(28)
Intangible assets, net	29	28
Total property equipment and intangible assets, net	$ 43	$ 41

Commitments, Contingencies an65

Commitments, Contingencies and Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments, Contingencies And Guarantees [Abstract]
Net Loss from Unsecured Customer Receivables	$ 116
Rent expense	15	$ 16	$ 14
Total future minimum annual lease commitments	$ 154

Commitments, Contingencies An66

Commitments, Contingencies And Guarantees (Minimum Annual Lease Commitments) (Details) $ in Millions	Dec. 31, 2017USD ($)
Commitments, Contingencies And Guarantees [Abstract]
2,018	$ 15
2,019	10
2,020	10
2,021	10
2,022	14
Thereafter	95
Total future minimum annual lease commitments	$ 154

Segment And Geographic Inform67

Segment And Geographic Information (Segment Table) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total net revenues	$ 1,702	$ 1,396	$ 1,189
Income before income taxes	1,049	761	458
Assets	61,162	54,673	48,734
Electronic Brokerage [Member]
Segment Reporting Information [Line Items]
Total net revenues	1,405	1,239	1,097
Income before income taxes	860	756	536
Assets	58,787	50,072	44,421
Market Making [Member]
Segment Reporting Information [Line Items]
Total net revenues	86	190	298
Income before income taxes	(27)	44	130
Assets	8,469	11,765	10,825
Corporate And Eliminations [Member]
Segment Reporting Information [Line Items]
Total net revenues	211	(33)	(206)
Income before income taxes	216	(39)	(208)
Assets	$ (6,094)	$ (7,164)	$ (6,512)

Segment And Geographic Inform68

Segment And Geographic Information (Geographic Table) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total net revenues	$ 1,702	$ 1,396	$ 1,189
Income before income taxes	1,049	761	458
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues	1,393	1,046	832
Income before income taxes	947	632	294
International [Member]
Segment Reporting Information [Line Items]
Total net revenues	309	350	357
Income before income taxes	$ 102	$ 129	$ 164

Regulatory Requirements (Narrat

Regulatory Requirements (Narrative) (Details) $ in Millions	Dec. 31, 2017USD ($)
Regulatory Requirements [Abstract]
Excess regulatory capital	$ 4,505

Regulatory Requirements (Summar

Regulatory Requirements (Summary Of Capital, Capital Requirements And Excess Capital) (Details) $ in Millions	Dec. 31, 2017USD ($)
Net Capital / Eligible Equity	$ 5,214
Required net capital	709
Excess regulatory capital	4,505
IB LLC [Member]
Net Capital / Eligible Equity	3,548
Required net capital	495
Excess regulatory capital	3,053
TH LLC [Member]
Net Capital / Eligible Equity	279
Required net capital	1
Excess regulatory capital	278
THE [Member]
Net Capital / Eligible Equity	614
Required net capital	92
Excess regulatory capital	522
Other Regulated Operating Companies [Member]
Net Capital / Eligible Equity	773
Required net capital	121
Excess regulatory capital	$ 652

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Related Party Transactions [Abstract]
Due from Related Parties - Customers	$ 250	$ 78
Due to Related Parties - Customers	$ 648	$ 468

Schedule I_Condensed Financia72

Schedule I—Condensed Financial Information of Registrant (Parent Company Only) (Condensed Statements Of Financial Conditions) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents	$ 1,732	$ 1,925	$ 1,601	$ 1,269
Total assets	61,162	54,673	48,734
Liabilities and stockholders' equity
Accrued expenses and other liabilities	147	80
Total liabilities	54,729	48,853
Stockholders’ equity:
Additional paid-in capital	832	775
Retained earnings	251	203
Accumulated other comprehensive income, net of income taxes of $0 and $1 at December 31, 2015 and 2014	9	(2)
Treasury stock, at cost, 133,294 and 134,439 shares as of December 31, 2017 and 2016	(3)	(3)
Total stockholders' equity	1,090	974
Total liabilities and stockholders' equity	$ 61,162	$ 54,673
Treasury stock shares	133,294	134,439
Common Class A
Stockholders’ equity:
Common stock	$ 1	$ 1
Common stock, par value	$ 0.01	$ 0.01
Shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	71,609,049	68,119,412
Common stock, shares outstanding	71,475,755	67,984,973
Common Class B
Stockholders’ equity:
Common stock
Shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100
Parent Company [Member]
Assets
Cash and cash equivalents			$ 1	$ 1
Investments in subsidiaries, equity basis	$ 1,122	$ 964
Other assets	156	297
Total assets	1,278	1,261
Liabilities and stockholders' equity
Payable to affiliates	187	285
Accrued expenses and other liabilities	1	2
Total liabilities	188	287
Stockholders’ equity:
Additional paid-in capital	832	775
Retained earnings	251	203
Accumulated other comprehensive income, net of income taxes of $0 and $1 at December 31, 2015 and 2014	9	(2)
Treasury stock, at cost, 133,294 and 134,439 shares as of December 31, 2017 and 2016	(3)	(3)
Total stockholders' equity	1,090	974
Total liabilities and stockholders' equity	1,278	1,261
Parent Company [Member] | Common Class A
Stockholders’ equity:
Common stock	1	1
Parent Company [Member] | Common Class B
Stockholders’ equity:
Common stock

Schedule I_Condensed Financia73

Schedule I—Condensed Financial Information of Registrant (Parent Company Only) (Condensed Statements Of Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income tax expense	$ 256	$ 62	$ 43
Net income	793	699	415
Net income available to common stockholders	76	84	49
Comprehensive income available for common stockholders	87	80	39
Parent Company [Member]
Loss before equity in income of subsidiary	92	(1)
Undistributed Gain Loss of Subsidiaries	147	117	67
Income tax expense	163	32	18
Net income	76	84	49
Net income available to common stockholders	76	84	49
Cumulative translation adjustment, net of tax	11	(4)	(10)
Comprehensive income available for common stockholders	$ 87	$ 80	$ 39

Schedule I_Condensed Financia74

Schedule I—Condensed Financial Information of Registrant (Parent Company Only) (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 793	$ 699	$ 415
Deferred income taxes	147	27	15
Gain on remeasurement of Tax Receivable Agreement liability	(93)
Net cash provided by operating activities	142	544	725
Net cash used in investing activities	(26)	(6)	(35)
Net cash used in financing activities	(374)	(189)	(295)
Effect of exchange rate changes on cash and cash equivalents	65	(25)	(63)
Net increase (decrease) in cash and cash equivalents	(193)	324	332
Cash and cash equivalents at beginning of period	1,925	1,601	1,269
Cash and cash equivalents at end of period	1,732	1,925	1,601
Cash paid for interest	209	77	68
Cash paid for taxes, net	47	29	31
Parent Company [Member]
Net income	76	84	49
Undistributed gains of subsidiaries, net	(147)	(117)	(67)
Deferred income taxes	149	30	13
Gain on remeasurement of Tax Receivable Agreement liability	(93)
Changes in operating assets and liabilities	(9)	9	9
Net cash provided by operating activities	(24)	6	4
Net cash used in investing activities	56	42	40
Net cash used in financing activities	(43)	(44)	(34)
Effect of exchange rate changes on cash and cash equivalents	11	(5)	(10)
Net increase (decrease) in cash and cash equivalents		(1)
Cash and cash equivalents at beginning of period		1	1
Cash and cash equivalents at end of period			$ 1
Cash paid for taxes, net	$ 13	(1)
Non Cash Distribution From Subsidiaries		$ 1

Schedule I_Condensed Financia75

Schedule I—Condensed Financial Information of Registrant (Parent Company Only) (Transactions With Affiliates) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule I—Condensed Financial Information of Registrant (Parent Company Only) [Abstract]
Receivables from affiliates	$ 0
Dividends received	56	$ 43	$ 40
Affiliate	$ 187	$ 285