Basis of Presentaion (Details)	Mar. 31, 2019 States
Basis Of Presentation [Abstract]
Number of States in which Entity Operates	11
Number of community regional banks operating in distinct geographical areas	7

Number of community/regional banks operating in distinct geographical areas

No definition available.

Name:	zion_NumberOfCommunityRegionalBanksOperatingInDistinctGeographicalAreas
Namespace Prefix:	zion_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant