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v3.25.3

OPERATING SEGMENT INFORMATION (Narrative) (Details) | 9 Months Ended
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Sep. 30, 2025 branch segment
Segment Reporting Information [Line Items] |
Number of bank operating segments | segment | 7
Number of branches | 408
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 | 77
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

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- Definition 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. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Definition Number Of Bank Operating Segments + References No definition available. + Details
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Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of Branches + References No definition available. + Details
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Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_WY
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_TX
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_AZ
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=zions_NationalBankOfArizonaSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_NV
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=zions_NevadaStateBankSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_CO
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=stpr_NM
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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