OPERATING SEGMENT INFORMATION (Narrative) (Details)	6 Months Ended
Jun. 30, 2025 branch segment
Segment Reporting Information [Line Items]
Number of bank operating segments \| segment	7
Number of branches	409
Utah \| Zions Bank
Segment Reporting Information [Line Items]
Number of branches	93
Idaho \| Zions Bank
Segment Reporting Information [Line Items]
Number of branches	25
Wyoming \| Zions Bank
Segment Reporting Information [Line Items]
Number of branches	1
California \| CB&T
Segment Reporting Information [Line Items]
Number of branches	78
California \| CB&T \| FirstBank Coachella Valley Branches
Segment Reporting Information [Line Items]
Number of branches	4
Texas \| Amegy
Segment Reporting Information [Line Items]
Number of branches	76
Arizona \| NBAZ
Segment Reporting Information [Line Items]
Number of branches	56
Nevada \| NSB
Segment Reporting Information [Line Items]
Number of branches	43
Colorado \| Vectra
Segment Reporting Information [Line Items]
Number of branches	33
New Mexico \| Vectra
Segment Reporting Information [Line Items]
Number of branches	1
Washington \| TCBW
Segment Reporting Information [Line Items]
Number of branches	2
Oregon \| TCBW
Segment Reporting Information [Line Items]
Number of branches	1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration