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

Noncredit-related losses recognized in other comprehensive income for debt securities held for which an other-than-temporary-impairment loss has been recognized in the period presented or previously.

No definition available.

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

Fair value of debt securities held for which an other-than-temporary-impairment loss has been recognized in the period presented or previously.

No definition available.

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

Amortized cost of debt securities held for which an other-than-temporary-impairment loss has been recognized in the period presented or previously.

No definition available.

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

- Details

Name:	ntrs_OtherThanTemporaryImpairmentNonCreditLossesRecognizedInEarningsLineItems
Namespace Prefix:	ntrs_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Total of accumulated other comprehensive loss related to that portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized either as available-for-sale or held-to-maturity that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14A

-URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669686-108580