2.2.0.25falsefalse40307 - Disclosure - Investment Securities (Schedule of Credit-Related Loss Activity Recognized in Earnings) (Details)truefalseIn Millionsfalse1falsefalseUSDfalsefalse1/1/2011 - 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$2true0us-gaap_InvestmentsAllOtherInvestmentsAbstractus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalse3false0stt_CreditRelatedLossesOtherThanTemporarilyImpairedBeginningBalancesttfalsecreditinstantCredit Related Losses Other Than Temporarily Impaired Beginning Balancefalsefalsefalsefalsefalsefalsefalsetruefalsefalseperiodstartlabel1truefalsefalse6300000063falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCredit Related Losses Other Than Temporarily Impaired Beginning BalanceNo authoritative reference available.falsefalse4false0stt_PlusExpectedCreditRelatedLossesForWhichOtherThanTemporaryImpairmentNotPreviouslyRecognizedsttfalsedebitdurationPlus Expected Credit Related Losses For Which Other Than Temporary Impairment Not Previously Recognizedfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse30000003falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryPlus Expected Credit Related Losses For Which Other Than Temporary Impairment Not Previously RecognizedNo authoritative reference available.falsefalse5false0stt_PlusExpectedCreditRelatedLossesForWhichOtherThanTemporaryImpairmentPreviouslyRecognizedsttfalsedebitdurationPlus Expected Credit Related Losses For Which Other Than Temporary Impairment Previously Recognizedfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse80000008falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryPlus Expected Credit Related Losses For Which Other Than Temporary Impairment Previously RecognizedNo authoritative reference available.falsefalse6false0stt_CreditRelatedLossesOtherThanTemporarilyImpairedClosingBalancesttfalsecreditinstantCredit-related losses other-than-temporarily impaired, ending balance, related to topic 310-30 securitiesfalsefalsefalsefalsefalsefalsefalsefalsetruefalseperiodendlabel1truefalsefalse7400000074falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCredit-related losses other-than-temporarily impaired, ending balance, related to topic 310-30 securitiesNo authoritative reference available.falsefalse15Investment Securities (Schedule of Credit-Related Loss Activity Recognized in Earnings) (Details) (USD $)MillionsUnKnownUnKnownUnKnownfalsetrue