XML 101 R49.htm IDEA: XBRL DOCUMENT v2.4.1.9
Book and Fair Values of All Financial Instruments (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Dec. 31, 2013
Assets        
Cash and Due from Banks $ 4,074.8us-gaap_CashAndDueFromBanks $ 3,050.6us-gaap_CashAndDueFromBanks $ 3,676.3us-gaap_CashAndDueFromBanks $ 3,162.4us-gaap_CashAndDueFromBanks
Federal Funds Sold and Resell Agreements 1,113.9us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell 1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell    
Interest-Bearing Deposits with Banks 15,432.3us-gaap_InterestBearingDepositsInBanks 14,928.3us-gaap_InterestBearingDepositsInBanks    
Federal Reserve Deposits 8,804.2us-gaap_FederalReserveBankStock 17,386.3us-gaap_FederalReserveBankStock    
Securities        
Available for Sale 30,945.7us-gaap_AvailableForSaleSecurities 29,558.5us-gaap_AvailableForSaleSecurities    
Held to Maturity 5,655.8us-gaap_HeldToMaturitySecurities 4,170.8us-gaap_HeldToMaturitySecurities    
Trading Account 1.4us-gaap_TradingSecurities 4.7us-gaap_TradingSecurities    
Loans (excluding Leases)        
Client Security Settlement Receivables 2,219.3ntrs_ClientSecuritySettlementReceivables 1,568.8ntrs_ClientSecuritySettlementReceivables    
Deposits        
Savings Certificates and Other Time 1,777.9us-gaap_TimeDeposits 1,757.4us-gaap_TimeDeposits    
Non U.S. Offices Interest-Bearing 45,942.2us-gaap_InterestBearingDepositLiabilitiesForeign 47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign    
Federal Funds Purchased 410.7us-gaap_FederalFundsPurchased 932.9us-gaap_FederalFundsPurchased    
Securities Sold under Agreements to Repurchase 613.2us-gaap_SecuritiesSoldUnderAgreementsToRepurchase 885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase    
Other Borrowings 2,874.1us-gaap_OtherBorrowings 1,685.2us-gaap_OtherBorrowings    
Senior Notes 1,497.1us-gaap_SeniorNotes 1,497.0us-gaap_SeniorNotes    
Long Term Debt (excluding Leases)        
Floating Rate Capital Debt 277.2ntrs_TrustPreferredSecurities 277.2ntrs_TrustPreferredSecurities    
Asset And Liability Management        
Derivative Instruments        
Assets 215.4us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
251.7us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities 53.6us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
48.7us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Client Related and Trading        
Derivative Instruments        
Assets 4,854.3us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
4,255.0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 4,805.7us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
4,173.3us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Carrying (Reported) Amount, Fair Value Disclosure        
Assets        
Cash and Due from Banks 4,074.8us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,050.6us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Funds Sold and Resell Agreements 1,113.9us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Interest-Bearing Deposits with Banks 15,432.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
14,928.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Reserve Deposits 8,804.2us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
17,386.3us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Securities        
Available for Sale 30,945.7us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[1] 29,558.5us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[2]    
Held to Maturity 5,655.8us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
4,170.8us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Trading Account 1.4us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
4.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Loans (excluding Leases)        
Held for Investment 31,503.8ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
30,458.0ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Held for Sale   2.5us-gaap_LoansReceivableHeldForSaleNet
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Client Security Settlement Receivables 2,219.3ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,568.8ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Other Assets        
Federal Reserve and Federal Home Loan Bank Stock 207.5us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
207.5us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Community Development Investments 198.4ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
209.9ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Employee Benefit and Deferred Compensation 162.1us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
143.2us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 39,016.4us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
41,454.6us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Savings Certificates and Other Time 1,777.9us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,757.4us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Non U.S. Offices Interest-Bearing 45,942.2us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Funds Purchased 410.7us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
932.9us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Securities Sold under Agreements to Repurchase 613.2us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Other Borrowings 2,874.1us-gaap_OtherBorrowings
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,685.2us-gaap_OtherBorrowings
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Senior Notes 1,497.1us-gaap_SeniorNotes
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,497.0us-gaap_SeniorNotes
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Long Term Debt (excluding Leases)        
Subordinated Debt 1,368.6us-gaap_SubordinatedLongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,583.3us-gaap_SubordinatedLongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Floating Rate Capital Debt 277.2ntrs_TrustPreferredSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
277.1ntrs_TrustPreferredSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Other Liabilities        
Standby Letters of Credit 58.3ntrs_StandbyLettersOfCredit
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
60.1ntrs_StandbyLettersOfCredit
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Loan Commitments 26.8us-gaap_CommitmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
28.3us-gaap_CommitmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts        
Derivative Instruments        
Assets 67.4us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
125.7us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities 27.7us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
23.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swaps        
Derivative Instruments        
Assets   126.8us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities   30.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Contracts        
Derivative Instruments        
Assets 148.9us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
     
Liabilities 28.9us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
     
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts        
Derivative Instruments        
Assets 4,731.2us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
4,149.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 4,686.4us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
4,072.0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Interest Rate Contracts        
Derivative Instruments        
Assets 123.1us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
105.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 119.3us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
101.3us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Estimate of Fair Value, Fair Value Disclosure        
Assets        
Cash and Due from Banks 4,074.8us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
3,050.6us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Funds Sold and Resell Agreements 1,113.9us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Interest-Bearing Deposits with Banks 15,432.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
14,928.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Reserve Deposits 8,804.2us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
17,386.3us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Securities        
Available for Sale 30,945.7us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
[1] 29,558.5us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
[2]    
Held to Maturity 5,665.0us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
4,176.1us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Trading Account 1.4us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
4.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Loans (excluding Leases)        
Held for Investment 31,747.7ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
30,600.4ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Held for Sale   2.5us-gaap_LoansReceivableHeldForSaleNet
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Client Security Settlement Receivables 2,219.3ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,568.8ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Other Assets        
Federal Reserve and Federal Home Loan Bank Stock 207.5us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
207.5us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Community Development Investments 198.7ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
210.8ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Benefit and Deferred Compensation 165.5us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
146.7us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 39,016.4us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
41,454.6us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Savings Certificates and Other Time 1,783.1us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,757.4us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Non U.S. Offices Interest-Bearing 45,942.2us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Funds Purchased 410.7us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
932.9us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Securities Sold under Agreements to Repurchase 613.2us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Other Borrowings 2,875.7us-gaap_OtherBorrowings
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,686.2us-gaap_OtherBorrowings
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Long Term Debt (excluding Leases)        
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Floating Rate Capital Debt 241.4ntrs_TrustPreferredSecurities
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242.8ntrs_TrustPreferredSecurities
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Other Liabilities        
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Loan Commitments 26.8us-gaap_CommitmentsFairValueDisclosure
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1        
Assets        
Cash and Due from Banks 4,074.8us-gaap_CashAndDueFromBanks
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Securities        
Available for Sale 4,627.4us-gaap_AvailableForSaleSecurities
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Other Assets        
Employee Benefit and Deferred Compensation 113.9us-gaap_DeferredCompensationPlanAssets
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96.7us-gaap_DeferredCompensationPlanAssets
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Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 39,016.4us-gaap_DemandDepositAccounts
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Federal Funds Sold and Resell Agreements 1,113.9us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
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Interest-Bearing Deposits with Banks 15,432.3us-gaap_InterestBearingDepositsInBanks
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14,928.3us-gaap_InterestBearingDepositsInBanks
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Federal Reserve Deposits 8,804.2us-gaap_FederalReserveBankStock
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17,386.3us-gaap_FederalReserveBankStock
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Securities        
Available for Sale 26,300.8us-gaap_AvailableForSaleSecurities
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Held to Maturity 5,665.0us-gaap_HeldToMaturitySecurities
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Trading Account 1.4us-gaap_TradingSecurities
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Loans (excluding Leases)        
Client Security Settlement Receivables 2,219.3ntrs_ClientSecuritySettlementReceivables
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1,568.8ntrs_ClientSecuritySettlementReceivables
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Other Assets        
Federal Reserve and Federal Home Loan Bank Stock 207.5us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
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Community Development Investments 198.7ntrs_AffordableHousingInvestment
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210.8ntrs_AffordableHousingInvestment
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Employee Benefit and Deferred Compensation 51.6us-gaap_DeferredCompensationPlanAssets
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Deposits        
Savings Certificates and Other Time 1,783.1us-gaap_TimeDeposits
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Non U.S. Offices Interest-Bearing 45,942.2us-gaap_InterestBearingDepositLiabilitiesForeign
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Federal Funds Purchased 410.7us-gaap_FederalFundsPurchased
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Securities Sold under Agreements to Repurchase 613.2us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
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Other Borrowings 2,875.7us-gaap_OtherBorrowings
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1,686.2us-gaap_OtherBorrowings
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Senior Notes 1,566.9us-gaap_SeniorNotes
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1,541.8us-gaap_SeniorNotes
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Long Term Debt (excluding Leases)        
Subordinated Debt 1,374.9us-gaap_SubordinatedLongTermDebt
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1,583.3us-gaap_SubordinatedLongTermDebt
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Floating Rate Capital Debt 241.4ntrs_TrustPreferredSecurities
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242.8ntrs_TrustPreferredSecurities
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Foreign Exchange Contracts        
Derivative Instruments        
Assets 67.4us-gaap_DerivativeFairValueOfDerivativeAsset
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Swaps        
Derivative Instruments        
Assets   126.8us-gaap_DerivativeFairValueOfDerivativeAsset
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Contracts        
Derivative Instruments        
Assets 148.9us-gaap_DerivativeFairValueOfDerivativeAsset
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Foreign Exchange Contracts        
Derivative Instruments        
Assets 4,731.2us-gaap_DerivativeFairValueOfDerivativeAsset
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4,149.5us-gaap_DerivativeFairValueOfDerivativeAsset
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/ us-gaap_FinancialInstrumentAxis
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Liabilities 4,686.4us-gaap_DerivativeFairValueOfDerivativeLiability
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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4,072.0us-gaap_DerivativeFairValueOfDerivativeLiability
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= ntrs_ClientRelatedAndTradingMember
   
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Contracts        
Derivative Instruments        
Assets 123.1us-gaap_DerivativeFairValueOfDerivativeAsset
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105.5us-gaap_DerivativeFairValueOfDerivativeAsset
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Liabilities 119.3us-gaap_DerivativeFairValueOfDerivativeLiability
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101.3us-gaap_DerivativeFairValueOfDerivativeLiability
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3        
Securities        
Available for Sale 17.5us-gaap_AvailableForSaleSecurities
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[1] 18.1us-gaap_AvailableForSaleSecurities
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[2]    
Loans (excluding Leases)        
Held for Investment 31,747.7ntrs_LoansReceivableHeldToMaturity
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30,600.4ntrs_LoansReceivableHeldToMaturity
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Held for Sale   2.5us-gaap_LoansReceivableHeldForSaleNet
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Other Liabilities        
Standby Letters of Credit 58.3ntrs_StandbyLettersOfCredit
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60.1ntrs_StandbyLettersOfCredit
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Loan Commitments $ 26.8us-gaap_CommitmentsFairValueDisclosure
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$ 28.3us-gaap_CommitmentsFairValueDisclosure
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[1] Refer to the table located on page 31 for the disaggregation of available for sale securities.
[2] Refer to the table located on page 32 for the disaggregation of available for sale securities.