Name:	ntrs_CommitmentsToExtendCredit
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents on-balance sheet credit risk to banks consisting primarily of interest bearing deposits with banks, federal funds sold, and securities purchased under agreements to resell.

No definition available.

Name:	ntrs_CreditRiskToBanks
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Credit Risk to Banks Non Interest Bearing Balances Held at Banks

No definition available.

Name:	ntrs_CreditRiskToBanksNonInterestBearingBalancesHeldAtBanks
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Loans and Leases Receivable, Residential, Real Estate

No definition available.

Name:	ntrs_LoansAndLeasesReceivableResidentialRealEstate
Namespace Prefix:	ntrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Lower Limit of Generally Required Loan to Collateral Value for Residential Real Estate Loans

No definition available.

Name:	ntrs_LowerLimitOfGenerallyRequiredLoanToCollateralValueForResidentialRealEstateLoans
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Residential Real Estate Loans Percentage Of Total US Loans and Leases

No definition available.

Name:	ntrs_ResidentialRealEstateLoansPercentageOfTotalUSLoansandLeases
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Upper Limit of Generally Required Loan to Collateral Value for Residential Real Estate loans

No definition available.

Name:	ntrs_UpperLimitOfGenerallyRequiredLoanToCollateralValueForResidentialRealEstateLoans
Namespace Prefix:	ntrs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_ConcentrationRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Includes: (1) the amount outstanding of funds lent to other depository institutions, securities brokers, or securities dealers in the form of Federal Funds sold; for example, immediately available funds lent under agreements or contracts that mature in one business day or roll over under a continuing contract, regardless of the nature of the transaction or the collateral involved, excluding overnight lending for commercial and industrial purposes. Also include Federal Funds sold under agreements to resell on a gross basis, excluding (1) sales of term Federal Funds, (2) due bills representing purchases of securities or other assets by the reporting bank that have not yet been delivered and similar instruments, (3) resale agreements that mature in more than one business day involving assets other than securities, and (4) yield maintenance dollar repurchase agreements (Federal Funds Sold) and (2) the dollar amount outstanding of funds lent in the form of security resale agreements regardless of maturity, if the agreement requires the bank to resell the identical security purchased or a security that meets the definition of substantially the same in the case of a dollar roll. Also include purchases of participations in pools of securities, regardless of maturity (Securities Purchased Under Agreements to Re-sell).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(m)(2)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878