Restrictions on Subsidiary Dividends and Loans or Advances - Additional Information (Detail)	Dec. 31, 2015
Banking and Thrift [Abstract]
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.

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