2.2.0.25truefalse40301 - Disclosure - Investment Securities (Narrative) (Details)truefalsefalse1falsefalseUSDfalsefalse1/1/2011 - 3/31/2011 USD ($) USD ($) / shares $Duration_1_1_2011_To_3_31_2011http://www.sec.gov/CIK0000093751duration2011-01-01T00:00:002011-03-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit15Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit13Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$2falsefalseUSDfalsefalse1/1/2010 - 3/31/2010 USD ($) USD ($) / shares $Duration_1_1_2010_To_3_31_2010http://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-03-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit15Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$3falsefalseUSDfalsefalse1/1/2010 - 12/31/2010 USD ($) $Duration_1_1_2010_To_12_31_2010http://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-12-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit15Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0Unit13Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$2false0us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledgedus-gaaptruedebitinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse4450000000044500000000falsetruefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse4481000000044810000000falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetarySum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS140-4 and FIN46(R)-8 -Paragraph B6 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 140 -Paragraph 17 -Subparagraph a(2) falsefalse3false0us-gaap_ImpairmentOfInvestmentsus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse1100000011000000falsefalsefalsefalsefalse2truefalsefalse9700000097000000falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis element represents the amount by which the carrying amount exceeds the fair value of the investment. The amount is charged to income if the decline in fair value is deemed to be other than temporary.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 falsefalse4false0stt_RecoveryOfClaimedAmountssttfalsenadurationModest Recovery of Claimed Amountsfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truetruefalse0.200.20falsefalsefalsefalsefalse2falsetruefalse00falsefalsefalsefalsefalse3falsetruefalse00falsefalsefalsefalsefalseOtherus-types:percentItemTypepureModest Recovery of Claimed AmountsNo authoritative reference available.falsefalse5false0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLossus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse14260000001426000000falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse15740000001574000000falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 22 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13, 19 falsefalse6false0us-gaap_MarketableSecuritiesRealizedGainLossus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsetruenegated1truefalsefalse-1600000000-1600000000falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity. Additionally, this item would include any losses recognized for other than temporary impairments of the subject investments in debt and equity securities.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 falsefalse7false0stt_NoOfInvestmentSecuritiessttfalsenainstantNo Of Investment Securitiesfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse20592059falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:integerItemTypeintegerNo Of Investment SecuritiesNo authoritative reference available.falsefalse8false0natruenanaNo definition available.falsetruefalsefalsefalsefalsefalsefalsefalsefalsehttp://www.statestreet.com/taxonomy/role/disclosureinvestmentsecuritiesnarrativedetails1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalseUSDtruefalse{invest_InvestmentAxis} : Asset-Backed Securities [Member] 1/1/2011 - 3/31/2011 USD ($) $Duration_1_1_2011_To_3_31_2011_invest_InvestmentAxis_us-gaap_AssetBackedSecuritiesMemberhttp://www.sec.gov/CIK0000093751duration2011-01-01T00:00:002011-03-31T00:00:00falsefalseAsset-Backed Securities [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AssetBackedSecuritiesMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$5falsefalseUSDtruefalse{invest_InvestmentAxis} : Asset-Backed Securities [Member] 1/1/2010 - 3/31/2010 USD ($) $Duration_1_1_2010_To_3_31_2010_invest_InvestmentAxis_us-gaap_AssetBackedSecuritiesMemberhttp://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-03-31T00:00:00falsefalseAsset-Backed Securities [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AssetBackedSecuritiesMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$6falsefalseUSDtruefalse{invest_InvestmentAxis} : Asset-Backed Securities [Member] 1/1/2010 - 12/31/2010 USD ($) $Duration_1_1_2010_To_12_31_2010_invest_InvestmentAxis_us-gaap_AssetBackedSecuritiesMemberhttp://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-12-31T00:00:00falsefalseAsset-Backed Securities [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AssetBackedSecuritiesMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$OthernaNo definition available.No authoritative reference available.falsefalse9false0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLossus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse10410000001041000000falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse11230000001123000000falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 22 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13, 19 falsefalse10false0stt_CreditRelatedLossesOtherThanTemporarilyImpairmentsttfalsedebitdurationCredit-related losses other-than-temporarily impairmentfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse20000002000000falsefalsefalsefalsefalse2truefalsefalse6600000066000000falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCredit-related losses other-than-temporarily impairmentNo authoritative reference available.falsefalse11false0natruenanaNo definition available.falsetruefalsefalsefalsefalsefalsefalsefalsefalsehttp://www.statestreet.com/taxonomy/role/disclosureinvestmentsecuritiesnarrativedetails1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse7falsefalseUSDtruefalse{invest_InvestmentAxis} : Sub-Prime [Member] 1/1/2011 - 3/31/2011 USD ($) $Duration_1_1_2011_To_3_31_2011_invest_InvestmentAxis_stt_SubPrimeMemberhttp://www.sec.gov/CIK0000093751duration2011-01-01T00:00:002011-03-31T00:00:00falsefalseSub-Prime [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldistt_SubPrimeMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$8falsefalseUSDtruefalse{invest_InvestmentAxis} : Sub-Prime [Member] 1/1/2010 - 3/31/2010 USD ($) $Duration_1_1_2010_To_3_31_2010_invest_InvestmentAxis_stt_SubPrimeMemberhttp://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-03-31T00:00:00falsefalseSub-Prime [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldistt_SubPrimeMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$9falsefalseUSDtruefalse{invest_InvestmentAxis} : Sub-Prime [Member] 1/1/2010 - 12/31/2010 USD ($) $Duration_1_1_2010_To_12_31_2010_invest_InvestmentAxis_stt_SubPrimeMemberhttp://www.sec.gov/CIK0000093751duration2010-01-01T00:00:002010-12-31T00:00:00falsefalseSub-Prime [Member]invest_InvestmentAxisxbrldihttp://xbrl.org/2006/xbrldistt_SubPrimeMemberinvest_InvestmentAxisexplicitMemberUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$OthernaNo definition available.No authoritative reference available.falsefalse12false0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLossus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse333000000333000000falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse346000000346000000falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. 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All or a portion of the unrealized holding loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 16 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 22 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13, 19 falsefalse13false0stt_CreditRelatedLossesOtherThanTemporarilyImpairmentsttfalsedebitdurationCredit-related losses other-than-temporarily impairmentfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse10000001000000falsefalsefalsefalsefalse2truefalsefalse10000001000000falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCredit-related losses other-than-temporarily impairmentNo authoritative reference available.falsefalse14false0natruenanaNo definition available.falsetruefalsefalsefalsefalsefalsefalsefalsefalsehttp://www.statestreet.com/taxonomy/role/disclosureinvestmentsecuritiesnarrativedetails1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse10falsefalseUSDtruefalse{invest_InvestmentAxis} : Alt-A [Member] 1/1/2011 - 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