Basis of Presentation (Details)	Sep. 30, 2020 state segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of states in which entity operates \| state	11
Number of community regional banks operating in distinct geographical areas \| segment	7

Number of community/regional banks operating in distinct geographical areas

No definition available.

Name:	zions_NumberOfCommunityRegionalBanksOperatingInDistinctGeographicalAreas
Namespace Prefix:	zions_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant