Restrictions on Subsidiary Dividends and Loans or Advances - Additional Information (Detail)	Dec. 31, 2014
Restrictions on Subsidiary Dividends and Loans or Advances [Line Items]
Regulatory limits on transfer of capital and surplus by a banking subsidiary to the Corporation and certain of its affiliates	10.00%ntrs_PercentageOfCapitalSurplus
Regulatory limits on aggregate transfer of capital and surplus by banking subsidiaries to the Corporation	20.00%

Maximum percentage limit based on capital and surplus the Bank may transfer to the Corporation and affiliates in the aggregate.

No definition available.

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