XML 59 R76.htm IDEA: XBRL DOCUMENT v2.4.1.9
Book and Fair Values of All Financial Instruments (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
ASSETS        
Cash and Due from Banks $ 3,050.6us-gaap_CashAndDueFromBanks $ 3,162.4us-gaap_CashAndDueFromBanks $ 3,752.7us-gaap_CashAndDueFromBanks $ 4,315.3us-gaap_CashAndDueFromBanks
Federal Funds Sold and Resell Agreements 1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell 529.6us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell    
Interest-Bearing Deposits with Banks 14,928.3us-gaap_InterestBearingDepositsInBanks 19,397.4us-gaap_InterestBearingDepositsInBanks    
Federal Reserve Deposits 17,386.3us-gaap_FederalReserveBankStock 12,911.5us-gaap_FederalReserveBankStock    
Securities        
Available for Sale 29,558.5us-gaap_AvailableForSaleSecurities 28,392.8us-gaap_AvailableForSaleSecurities    
Held to Maturity 4,170.8us-gaap_HeldToMaturitySecurities 2,325.8us-gaap_HeldToMaturitySecurities    
Trading Account 4.7us-gaap_TradingSecurities 1.7us-gaap_TradingSecurities    
Loans (excluding Leases)        
Client Security Settlement Receivables 1,568.8ntrs_ClientSecuritySettlementReceivables 1,355.2ntrs_ClientSecuritySettlementReceivables    
Deposits        
Savings Certificates and Other Time 1,757.4us-gaap_TimeDeposits 1,874.4us-gaap_TimeDeposits    
Non-U.S. Offices Interest-Bearing 47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign 48,461.7us-gaap_InterestBearingDepositLiabilitiesForeign    
Federal Funds Purchased 932.9us-gaap_FederalFundsPurchased 965.1us-gaap_FederalFundsPurchased    
Securities Sold under Agreements to Repurchase 885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase 917.3us-gaap_SecuritiesSoldUnderAgreementsToRepurchase    
Other Borrowings 1,685.2us-gaap_OtherBorrowings 1,558.6us-gaap_OtherBorrowings    
Senior Notes 1,497.0us-gaap_SeniorNotes [1],[2] 1,996.6us-gaap_SeniorNotes [1],[2]    
Long Term Debt (excluding Leases)        
Federal Home Loan Bank Borrowings   135.0us-gaap_FederalHomeLoanBankAdvancesLongTerm    
Floating Rate Capital Debt 277.2ntrs_TrustPreferredSecurities 277.1ntrs_TrustPreferredSecurities    
Other Liabilities        
Contingent Consideration   55.4us-gaap_BusinessCombinationContingentConsiderationLiability    
Asset And Liability Management        
DERIVATIVE INSTRUMENTS        
Assets 251.7us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
135.1us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities 48.7us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
136.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Client Related and Trading        
DERIVATIVE INSTRUMENTS        
Assets 4,255.0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
2,967.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 4,173.3us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
2,963.2us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Carrying (Reported) Amount, Fair Value Disclosure        
ASSETS        
Cash and Due from Banks 3,050.6us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,162.4us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Funds Sold and Resell Agreements 1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
529.6us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Interest-Bearing Deposits with Banks 14,928.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
19,397.4us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Reserve Deposits 17,386.3us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
12,911.5us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Securities        
Available for Sale 29,558.5us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[3] 28,392.8us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[4]    
Held to Maturity 4,170.8us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
2,325.8us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Trading Account 4.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Loans (excluding Leases)        
Held for Investment 30,458.0ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
28,136.5ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Held for Sale 2.5us-gaap_LoansReceivableHeldForSaleNet
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
     
Client Security Settlement Receivables 1,568.8ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,355.2ntrs_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
194.7us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Community Development Investments 209.9ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
228.1ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Employee Benefit and Deferred Compensation 143.2us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
132.7us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 41,454.6us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
33,762.0us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Savings Certificates and Other Time 1,757.4us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,874.4us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Non-U.S. Offices Interest-Bearing 47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
48,461.7us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Funds Purchased 932.9us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
965.1us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Securities Sold under Agreements to Repurchase 885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
917.3us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Other Borrowings 1,685.2us-gaap_OtherBorrowings
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,558.6us-gaap_OtherBorrowings
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Senior Notes 1,497.0us-gaap_SeniorNotes
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,996.6us-gaap_SeniorNotes
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Long Term Debt (excluding Leases)        
Subordinated Debt 1,583.3us-gaap_SubordinatedLongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,537.3us-gaap_SubordinatedLongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Federal Home Loan Bank Borrowings   135.0us-gaap_FederalHomeLoanBankAdvancesLongTerm
/ 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 60.1ntrs_StandbyLettersOfCredit
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
59.6ntrs_StandbyLettersOfCredit
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Contingent Consideration   55.4us-gaap_BusinessCombinationContingentConsiderationLiability
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Loan Commitments 28.3us-gaap_CommitmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
35.7us-gaap_CommitmentsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
   
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts        
DERIVATIVE INSTRUMENTS        
Assets 125.7us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
21.0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities 23.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
59.5us-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   115.1us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
   
Liabilities   78.2us-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 126.8us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_AssetAndLiabilityManagementMember
     
Liabilities 30.5us-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 4,149.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
2,844.7us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 4,072.0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
2,846.2us-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 105.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
122.8us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
   
Liabilities 101.3us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateContractMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ us-gaap_FinancialInstrumentAxis
= ntrs_ClientRelatedAndTradingMember
117.0us-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 3,050.6us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
3,162.4us-gaap_CashAndDueFromBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Funds Sold and Resell Agreements 1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
529.6us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Interest-Bearing Deposits with Banks 14,928.3us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
19,397.4us-gaap_InterestBearingDepositsInBanks
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Reserve Deposits 17,386.3us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
12,911.5us-gaap_FederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Securities        
Available for Sale 29,558.5us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
[3] 28,392.8us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
[4]    
Held to Maturity 4,176.1us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
2,321.4us-gaap_HeldToMaturitySecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Trading Account 4.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1.7us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Loans (excluding Leases)        
Held for Investment 30,600.4ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
28,147.2ntrs_LoansReceivableHeldToMaturity
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Held for Sale 2.5us-gaap_LoansReceivableHeldForSaleNet
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
     
Client Security Settlement Receivables 1,568.8ntrs_ClientSecuritySettlementReceivables
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,355.2ntrs_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
194.7us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Community Development Investments 210.8ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
227.8ntrs_AffordableHousingInvestment
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Benefit and Deferred Compensation 146.7us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
126.9us-gaap_DeferredCompensationPlanAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 41,454.6us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
33,762.0us-gaap_DemandDepositAccounts
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Savings Certificates and Other Time 1,757.0us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,877.1us-gaap_TimeDeposits
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Non-U.S. Offices Interest-Bearing 47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
48,461.7us-gaap_InterestBearingDepositLiabilitiesForeign
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Federal Funds Purchased 932.9us-gaap_FederalFundsPurchased
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
965.1us-gaap_FederalFundsPurchased
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Securities Sold under Agreements to Repurchase 885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
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Other Borrowings 1,686.2us-gaap_OtherBorrowings
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Long Term Debt (excluding Leases)        
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Federal Home Loan Bank Borrowings   137.2us-gaap_FederalHomeLoanBankAdvancesLongTerm
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Floating Rate Capital Debt 242.8ntrs_TrustPreferredSecurities
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230.2ntrs_TrustPreferredSecurities
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Other Liabilities        
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59.6ntrs_StandbyLettersOfCredit
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Contingent Consideration   55.4us-gaap_BusinessCombinationContingentConsiderationLiability
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DERIVATIVE INSTRUMENTS        
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1        
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Cash and Due from Banks 3,050.6us-gaap_CashAndDueFromBanks
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3,162.4us-gaap_CashAndDueFromBanks
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Securities        
Available for Sale 4,506.9us-gaap_AvailableForSaleSecurities
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[3] 1,917.9us-gaap_AvailableForSaleSecurities
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[4]    
Other Assets        
Employee Benefit and Deferred Compensation 96.7us-gaap_DeferredCompensationPlanAssets
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Deposits        
Demand, Noninterest-Bearing, Savings and Money Market 41,454.6us-gaap_DemandDepositAccounts
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2        
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Federal Funds Sold and Resell Agreements 1,062.7us-gaap_FederalFundsSoldAndSecuritiesPurchasedUnderAgreementsToResell
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Interest-Bearing Deposits with Banks 14,928.3us-gaap_InterestBearingDepositsInBanks
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Federal Reserve Deposits 17,386.3us-gaap_FederalReserveBankStock
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12,911.5us-gaap_FederalReserveBankStock
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Securities        
Available for Sale 25,033.5us-gaap_AvailableForSaleSecurities
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Held to Maturity 4,176.1us-gaap_HeldToMaturitySecurities
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Trading Account 4.7us-gaap_TradingSecurities
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Loans (excluding Leases)        
Client Security Settlement Receivables 1,568.8ntrs_ClientSecuritySettlementReceivables
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1,355.2ntrs_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 210.8ntrs_AffordableHousingInvestment
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227.8ntrs_AffordableHousingInvestment
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Employee Benefit and Deferred Compensation 50.0us-gaap_DeferredCompensationPlanAssets
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Deposits        
Savings Certificates and Other Time 1,757.0us-gaap_TimeDeposits
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Non-U.S. Offices Interest-Bearing 47,545.0us-gaap_InterestBearingDepositLiabilitiesForeign
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48,461.7us-gaap_InterestBearingDepositLiabilitiesForeign
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Federal Funds Purchased 932.9us-gaap_FederalFundsPurchased
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Securities Sold under Agreements to Repurchase 885.1us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
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Other Borrowings 1,686.2us-gaap_OtherBorrowings
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Senior Notes 1,541.8us-gaap_SeniorNotes
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Long Term Debt (excluding Leases)        
Subordinated Debt 1,583.4us-gaap_SubordinatedLongTermDebt
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Federal Home Loan Bank Borrowings   137.2us-gaap_FederalHomeLoanBankAdvancesLongTerm
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Floating Rate Capital Debt 242.8ntrs_TrustPreferredSecurities
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230.2ntrs_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        
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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        
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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 126.8us-gaap_DerivativeFairValueOfDerivativeAsset
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Liabilities 30.5us-gaap_DerivativeFairValueOfDerivativeLiability
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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 4,149.5us-gaap_DerivativeFairValueOfDerivativeAsset
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2,844.7us-gaap_DerivativeFairValueOfDerivativeAsset
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Liabilities 4,072.0us-gaap_DerivativeFairValueOfDerivativeLiability
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2,846.2us-gaap_DerivativeFairValueOfDerivativeLiability
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Contracts        
DERIVATIVE INSTRUMENTS        
Assets 105.5us-gaap_DerivativeFairValueOfDerivativeAsset
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122.8us-gaap_DerivativeFairValueOfDerivativeAsset
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Liabilities 101.3us-gaap_DerivativeFairValueOfDerivativeLiability
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117.0us-gaap_DerivativeFairValueOfDerivativeLiability
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Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3        
Securities        
Available for Sale 18.1us-gaap_AvailableForSaleSecurities
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[3] 98.9us-gaap_AvailableForSaleSecurities
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[4]    
Loans (excluding Leases)        
Held for Investment 30,600.4ntrs_LoansReceivableHeldToMaturity
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28,147.2ntrs_LoansReceivableHeldToMaturity
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Held for Sale 2.5us-gaap_LoansReceivableHeldForSaleNet
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Other Liabilities        
Standby Letters of Credit 60.1ntrs_StandbyLettersOfCredit
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59.6ntrs_StandbyLettersOfCredit
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Contingent Consideration   55.4us-gaap_BusinessCombinationContingentConsiderationLiability
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Loan Commitments $ 28.3us-gaap_CommitmentsFairValueDisclosure
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$ 35.7us-gaap_CommitmentsFairValueDisclosure
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[1] Not redeemable prior to maturity.
[2] Debt issue costs are recorded as an asset and amortized on a straight-line basis over the life of the Note.
[3] Refer to the table located on page 87 for the disaggregation of available for sale securities.
[4] Refer to the table located on page 88 for the disaggregation of available for sale securities.