Organization and Description of the Business	12 Months Ended
Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of the Business	Organization and Description of the Business KCG Holdings, Inc. (collectively with its subsidiaries, "KCG" or the "Company") is a leading independent securities firm offering clients a range of services designed to address trading needs across asset classes, product types and time zones. The Company combines advanced technology with specialized client service across market making, agency execution and trading venues and also engages in principal trading via direct-to-client and non-client exchange-based electronic market making. KCG has multiple access points to trade global equities, options, futures, fixed income, currencies and commodities via voice or automated execution. On December 19, 2012, Knight Capital Group, Inc.(“Knight”) and GETCO Holding Company, LLC (“GETCO”) entered into an agreement and plan of merger (as amended and restated on April 15, 2013, the “Merger Agreement”) for a series of strategic business combinations (the “Mergers”). The Mergers were approved by the respective stockholders and unitholders of both companies at special meetings held on June 25, 2013, and the Mergers were completed on July 1, 2013. As a result of the Mergers, Knight and GETCO each became a wholly-owned subsidiary of KCG. The Mergers took place in order to combine the businesses, intellectual capital and resources of the two companies to more successfully compete in the highly regulated and technologically advanced marketplace and to allow for further diversification of each company's revenues from principal and agency trading across asset classes and regions. The Mergers were treated as a purchase of Knight by GETCO for accounting and financial reporting purposes. As a result, the financial results for the year ended December 31, 2013 comprise six months of results of KCG plus six months of GETCO and the financial results for the year ended December 31, 2014 comprise the results of KCG. All periods prior to 2013 reflect solely the results and financial condition of GETCO. As of December 31, 2014, the Company's operating segments comprised the following: (i) Market Making; (ii) Global Execution Services; and (iii) Corporate and Other. Market Making The Market Making segment principally consists of market making in the cash, futures and options markets across global equities, options, fixed income, currencies and commodities. As a market maker, the Company commits capital on a principal basis by offering to buy securities from, or sell securities to, broker dealers, banks and institutions. Principal trading in the Market Making segment primarily consists of direct-to-client and non-client exchange-based electronic market making, including trade executions conducted as an equities Designated Market Maker (“DMM”) on the New York Stock Exchange ("NYSE") and NYSE Amex Equities ("NYSE Amex"). The Company is an active participant on all major global equity and futures exchanges and also trades on substantially all domestic electronic options exchanges. As a complement to electronic market making, the Company’s cash trading business handles specialized orders and also transacts on the OTC Bulletin Board, marketplaces operated by the OTC Markets Group Inc. and the Alternative Investment Market (“AIM”) of the London Stock Exchange. Global Execution Services The Global Execution Services segment comprises agency execution services and trading venues, offering trading in global equities, futures, options, foreign exchange, and fixed income to institutions, banks and broker dealers. The Company generally earns commissions as an agent between principals for transactions that are executed within this segment; however, the Company may commit capital on behalf of clients as needed. Agency-based, execution-only trading in the segment is done primarily through a variety of access points including: (i) algorithmic trading and order routing in global equities; (ii) institutional sales traders executing program, block and riskless principal trades in global equities and exchange traded funds ("ETFs"); (iii) an institutional spot foreign exchange electronic communication network ("ECN"); (iv) a fixed income ECN that also offers trading applications; and (v) an alternative trading system ("ATS") for global equities. Corporate and Other The Corporate and Other segment invests principally in strategic financial services-oriented opportunities; allocates, deploys and monitors all capital; and maintains corporate overhead expenses and all other income and expenses that are not attributable to the other segments. The Corporate and Other segment also contains functions that support the Company’s other segments such as self-clearing services, including stock lending activities. Discontinued Businesses Management from time to time conducts a strategic review of its businesses and evaluates their potential value in the marketplace relative to their current and expected returns. To the extent management and the Company's Board of Directors determine a business may return a higher value to stockholders, or is no longer core to our strategy, the Company may divest or exit such business. In November 2013 KCG sold Urban Financial of America, LLC, (“Urban”), the reverse mortgage origination and securitization business that was previously owned by Knight to an investor group. In November 2014, KCG sold certain assets and liabilities related to its Futures Commission Merchant (“FCM”) business to Wedbush Securities Inc. In October 2014, the Company announced that it began to explore strategic options for KCG Hotspot, the Company's spot institutional foreign exchange ECN, with the goal of executing on opportunities if it created additional value for the Company's stockholders, clients and employees. See Footnote 4 "Discontinued Operations & Assets and Liabilities Held for Sale" and Footnote 27 "Subsequent Event" for additional information.

Organization and Description of the Business

KCG Holdings, Inc. (collectively with its subsidiaries, "KCG" or the "Company") is a leading independent securities firm offering clients a range of services designed to address trading needs across asset classes, product types and time zones. The Company combines advanced technology with specialized client service across market making, agency execution and trading venues and also engages in principal trading via direct-to-client and non-client exchange-based electronic market making. KCG has multiple access points to trade global equities, options, futures, fixed income, currencies and commodities via voice or automated execution.

On December 19, 2012, Knight Capital Group, Inc.(“Knight”) and GETCO Holding Company, LLC (“GETCO”) entered into an agreement and plan of merger (as amended and restated on April 15, 2013, the “Merger Agreement”) for a series of strategic business combinations (the “Mergers”). The Mergers were approved by the respective stockholders and unitholders of both companies at special meetings held on June 25, 2013, and the Mergers were completed on July 1, 2013. As a result of the Mergers, Knight and GETCO each became a wholly-owned subsidiary of KCG.

The Mergers took place in order to combine the businesses, intellectual capital and resources of the two companies to more successfully compete in the highly regulated and technologically advanced marketplace and to allow for further diversification of each company's revenues from principal and agency trading across asset classes and regions. The Mergers were treated as a purchase of Knight by GETCO for accounting and financial reporting purposes. As a result, the financial results for the year ended December 31, 2013 comprise six months of results of KCG plus six months of GETCO and the financial results for the year ended December 31, 2014 comprise the results of KCG. All periods prior to 2013 reflect solely the results and financial condition of GETCO.

As of December 31, 2014, the Company's operating segments comprised the following: (i) Market Making; (ii) Global Execution Services; and (iii) Corporate and Other.

Market Making

The Market Making segment principally consists of market making in the cash, futures and options markets across global equities, options, fixed income, currencies and commodities. As a market maker, the Company commits capital on a principal basis by offering to buy securities from, or sell securities to, broker dealers, banks and institutions. Principal trading in the Market Making segment primarily consists of direct-to-client and non-client exchange-based electronic market making, including trade executions conducted as an equities Designated Market Maker (“DMM”) on the New York Stock Exchange ("NYSE") and NYSE Amex Equities ("NYSE Amex"). The Company is an active participant on all major global equity and futures exchanges and also trades on substantially all domestic electronic options exchanges. As a complement to electronic market making, the Company’s cash trading business handles specialized orders and also transacts on the OTC Bulletin Board, marketplaces operated by the OTC Markets Group Inc. and the Alternative Investment Market (“AIM”) of the London Stock Exchange.

Global Execution Services

The Global Execution Services segment comprises agency execution services and trading venues, offering trading in global equities, futures, options, foreign exchange, and fixed income to institutions, banks and broker dealers. The Company generally earns commissions as an agent between principals for transactions that are executed within this segment; however, the Company may commit capital on behalf of clients as needed. Agency-based, execution-only trading in the segment is done primarily through a variety of access points including: (i) algorithmic trading and order routing in global equities; (ii) institutional sales traders executing program, block and riskless principal trades in global equities and exchange traded funds ("ETFs"); (iii) an institutional spot foreign exchange electronic communication network ("ECN"); (iv) a fixed income ECN that also offers trading applications; and (v) an alternative trading system ("ATS") for global equities.

Corporate and Other

The Corporate and Other segment invests principally in strategic financial services-oriented opportunities; allocates, deploys and monitors all capital; and maintains corporate overhead expenses and all other income and expenses that are not attributable to the other segments. The Corporate and Other segment also contains functions that support the Company’s other segments such as self-clearing services, including stock lending activities.

Discontinued Businesses

Management from time to time conducts a strategic review of its businesses and evaluates their potential value in the marketplace relative to their current and expected returns. To the extent management and the Company's Board of Directors determine a business may return a higher value to stockholders, or is no longer core to our strategy, the Company may divest or exit such business.

In November 2013 KCG sold Urban Financial of America, LLC, (“Urban”), the reverse mortgage origination and securitization business that was previously owned by Knight to an investor group.

In November 2014, KCG sold certain assets and liabilities related to its Futures Commission Merchant (“FCM”) business to Wedbush Securities Inc.

In October 2014, the Company announced that it began to explore strategic options for KCG Hotspot, the Company's spot institutional foreign exchange ECN, with the goal of executing on opportunities if it created additional value for the Company's stockholders, clients and employees.

See Footnote 4 "Discontinued Operations & Assets and Liabilities Held for Sale" and Footnote 27 "Subsequent Event" for additional information.