Basis of Presentation	3 Months Ended
Basis of Presentation	Mar. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accounting and financial reporting policies of State Street Corporation conform to U.S. generally accepted accounting principles, referred to as GAAP. State Street Corporation, the parent company, is a financial holding company headquartered in Boston, Massachusetts. Unless otherwise indicated or unless the context requires otherwise, all references in these condensed notes to consolidated financial statements to “State Street,” “we,” “us,” “our” or similar references mean State Street Corporation and its subsidiaries on a consolidated basis. Our principal banking subsidiary is State Street Bank and Trust Company, or State Street Bank. We have two lines of business: Investment Servicing provides services for mutual funds, collective investment funds and other investment pools, corporate and public retirement plans, insurance companies, foundations and endowments worldwide. Products include custody, product- and participant-level accounting, daily pricing and administration; master trust and master custody; record-keeping; foreign exchange, brokerage and other trading services; securities finance; deposit and short-term investment facilities; loans and lease financing; investment manager and alternative investment manager operations outsourcing; and performance, risk and compliance analytics to support institutional investors. Investment Management, through State Street Global Advisors, or SSgA, provides a broad range of investment management strategies, specialized investment management advisory services and other financial services, such as securities finance, for corporations, public funds, and other sophisticated investors. Management strategies offered by SSgA include passive and active, such as enhanced indexing, using quantitative and fundamental methods for both U.S. and non-U.S. equity and fixed-income securities. SSgA also offers exchange-traded funds. The consolidated financial statements accompanying these condensed notes are unaudited. In the opinion of management, all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the consolidated results of operations in these financial statements, have been made. Certain previously reported amounts presented in this Form 10-Q have been reclassified to conform to current-period presentation. Events occurring subsequent to the date of our consolidated statement of condition were evaluated for potential recognition or disclosure in our consolidated financial statements through the date we filed this Form 10-Q with the SEC. The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions in the application of certain of our significant accounting policies that may materially affect the reported amounts of assets, liabilities, equity, revenue and expenses. As a result of unanticipated events or circumstances, actual results could differ from those estimates. Amounts dependent on subjective or complex judgments in the application of accounting policies considered by management to be relatively more significant in this regard are those associated with our accounting for fair-value measurements; other-than-temporary impairment of investment securities; and impairment of goodwill and other intangible assets. Among other effects, unanticipated events or circumstances could result in future impairment of investment securities, goodwill or other intangible assets. Our consolidated statement of condition at December 31, 2012 included in the accompanying consolidated financial statements was derived from the audited financial statements at that date, but does not include all notes required by GAAP for a complete set of financial statements. The accompanying consolidated financial statements and these condensed notes should be read in conjunction with the financial and risk factors information included in our 2012 Form 10-K, which we previously filed with the SEC.

The entire disclosure for the organization, consolidation and basis of presentation of financial statements disclosure, and significant accounting policies of the reporting entity. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. Describes procedure if disclosures are provided in more than one note to the financial statements.

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