2.2.0.25falsefalse21202 - Disclosure - Variable Interest Entities (Policy)truefalsefalse1falsefalseUSDfalsefalse1/1/2010 - 12/31/2010 USD ($) USD ($) / shares $Duration_1_1_2010_To_12_31_2010http://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-12-31T00:00:00Unit15Standardhttp://xbrl.us/us-types/2009-01-31sqftxbrlus0Unit13Standardhttp://www.xbrl.org/2003/instancepurexbrli0Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit14Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDUSD$5false0stt_AssetBackedSecuritizationTrustsPolicyTextBlocksttfalsenadurationAsset-Backed Securitization Trusts Policy [Text Block]falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00<div> <div> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">We are involved with various types of special purpose entities, some of which are variable interest entities, or VIEs, as defined by GAAP. Some of these special purpose entities are recorded in our consolidated financial statements. We also invest in various forms of asset-backed securities, which we carry in our investment securities portfolio. These asset-backed securities meet the GAAP definition of asset securitization entities, which entities are considered to be VIEs. We are not considered to be the primary beneficiary of these VIEs, as defined by GAAP, since we do not have control over their activities. Additional information about asset-backed securities is provided in note 3. </font></p></div> </div>We are involved with various types of special purpose entities, some of which are variable interest entities, or VIEs, as defined by GAAP. Some of thesefalsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringAsset-Backed Securitization Trusts Policy [Text Block]No authoritative reference available.falsefalse6false0stt_ComponentsOfTaxExemptInvestmentProgramPolicyTextBlocksttfalsenadurationComponents of Tax-Exempt Investment Program Policy [Text Block]falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00<div> <div> <p style="margin-top: 12px; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">Tax-Exempt Investment Program: </font></p> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">In the normal course of our business, we structure and sell certificated interests in pools of tax-exempt investment-grade assets, principally to our mutual fund customers. We structure these pools as partnership trusts, and the trusts are recorded in our consolidated statement of condition as investment securities available for sale and other short-term borrowings. We may also provide liquidity and re-marketing services to the trusts. As of December&nbsp;31, 2010 and 2009, we carried investment securities available for sale, composed of securities related to state and political subdivisions, with a fair value of $<font class="_mt">2.85</font> billion and $<font class="_mt">3.13</font> billion, respectively, and other short-term borrowings (see note 8) of $<font class="_mt">2.50</font> billion and $<font class="_mt">2.74< ;/font> billion, respectively, in our consolidated statement of condition in connection with these trusts. </font></p> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">We transfer assets to the trusts from our investment securities portfolio at adjusted book value, and the trusts finance the acquisition of these assets by selling certificated interests issued by the trusts to third-party investors and to State Street as residual holder. These transfers do not meet the de-recognition criteria defined by GAAP<i>,</i> and therefore are recorded in our consolidated financial statements. The trusts had a weighted-average life of approximately&nbsp;<font class="_mt">7.7</font> years at December&nbsp;31, 2010, compared to approximately&nbsp;<font class="_mt">8.1</font>&nbsp;years at December&nbsp;31, 2009. Under separate legal agreements, we provide standby bond purchase agreements to these trusts, which obligate State Street to acquire the certificated interests at par value in the ev ent that the re-marketing agent is unable to place the certificated interests with investors. Our obligations as standby bond purchase agreement provider terminate in the event of the following credit events: payment default, bankruptcy of the issuer and the credit enhancer, if any, the imposition of taxability, or the downgrade of an asset held by the trust below investment grade. Our commitments to the trusts under these standby bond purchase agreements totaled $<font class="_mt">2.80</font> billion at December&nbsp;31, 2010, none of which was utilized at period-end. In the event that our obligations under these agreements are triggered, no material impact to our consolidated results of operations or financial condition is expected to occur, because the securities are already recorded at fair value in our consolidated statement of condition.</font></p></div> </div>Tax-Exempt Investment Program: In the normal course of our business, we structure and sell certificated interests in pools of tax-exempt investment-gradefalsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringComponents of Tax-Exempt Investment Program Policy [Text Block]No authoritative reference available.falsefalse7false0stt_ScheduleOfAssetBackedCommercialPaperProgra mPolicyTextBlocksttfalsenadurationSchedule of Asset-Backed Commercial Paper Program Policy [Text Block]falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00<div> <p style="margin-top: 12px; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">Asset-Backed Commercial Paper Program: </font></p> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">We sponsor and administer multi-seller asset-backed commercial paper programs, or conduits, which are recorded in our consolidated financial statements. These conduits, the first of which was established in 1992, were originally designed to satisfy the demand of our institutional clients, particularly mutual fund customers, for commercial paper. The conduits purchase financial assets with various asset classification from a variety of independent third parties and obtain funding through the issuance of the above-described commercial paper. We consider the activities of the conduits in our liquidity management process, and offer the program to our clients to fund the conduits' assets. The conduits hold diversified investments, which are primarily asset-backed securities purchased from independent third parties, collateralized by student loans, automobile and equipment l oans and credit card receivables, among other asset types. </font></p> </div>Asset-Backed Commercial Paper Program: We sponsor and administer multi-seller asset-backed commercial paper programs, or conduits, which are recorded in ourfalsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringSchedule of Asset-Backed Commercial Paper Program Policy [Text Block]No authoritative reference available.falsefalse8false0stt_CollateralizedDebtObligationsPolicyTextBlocksttfalsenadurationCollateralized Debt Obligations Policy [Text Block]falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00<div> <div> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"> </p> <p style="margin-top: 12px; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">Collateralized Debt Obligations: </font></p> <p style="margin-top: 6px; text-indent: 4%; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">We serve as collateral manager for a series of collateralized debt obligations, referred to as CDOs. A CDO is a structured investment vehicle which purchases a portfolio of assets funded through the issuance of several classes of debt and equity, the repayment of and return on which are linked to the performance of the underlying assets. We have determined that we are not the primary beneficiary of these VIEs, and do not record them in our consolidated financial statements. At December&nbsp;31, 2010 and 2009, the aggregate notional value of these CDOs was $<font class="_mt">1.0</font> billion and $<font class="_mt">2.0</font>&nbsp;billion, respectively. At December&nbsp;31, 2010 and 2009, the carrying value of the underlying collateral was $<font class="_mt">323</font> million and $<font class="_mt">1.2</font> billion, respectively. We did not acquire or transfer any investment securities to a CDO during 2010 or 2009. </font></p></div> </div>Collateralized Debt Obligations: We serve as collateral manager for a series of collateralized debt obligations, referred to as CDOs. A CDO is a structuredfalsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringCollateralized Debt Obligations Policy [Text Block]No authoritative reference available.falsefalse14Variable Interest Entities (Policy)U nKnownUnKnownUnKnownUnKnownfalsetrue