Securities Sold Under Agreements to Repurchase (Narrative) (Details) $ in Billions	Mar. 31, 2026 USD ($)
Transfers and Servicing [Abstract]
Repurchase receivable	$ 4.6

Assets Sold Under Agreements To Repurchase, Repurchase Receivable

No definition available.

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