LOANS, LEASES, AND ALLOWANCE FOR CREDIT LOSSES (Summary of Nonaccrual Loans) (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	$ 96	$ 95
Amortized cost basis with allowance	196	220
Nonaccrual loans that are current	292	315
Related allowance	38	36
Commercial:
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	48	77
Amortized cost basis with allowance	104	69
Nonaccrual loans that are current	152	146
Related allowance	22	20
Commercial: \| Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	18	44
Amortized cost basis with allowance	78	49
Nonaccrual loans that are current	96	93
Related allowance	21	19
Commercial: \| Owner-occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	28	33
Amortized cost basis with allowance	26	18
Nonaccrual loans that are current	54	51
Related allowance	1	1
Commercial: \| Municipal
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	2	0
Amortized cost basis with allowance	0	2
Nonaccrual loans that are current	2	2
Related allowance	0	0
Commercial real estate:
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	32	4
Amortized cost basis with allowance	2	69
Nonaccrual loans that are current	34	73
Related allowance	0	2
Commercial real estate: \| Term
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	32	4
Amortized cost basis with allowance	2	68
Nonaccrual loans that are current	34	72
Related allowance	0	2
Commercial real estate: \| Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance		0
Amortized cost basis with allowance		1
Nonaccrual loans that are current		1
Related allowance		0
Consumer:
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	16	14
Amortized cost basis with allowance	90	82
Nonaccrual loans that are current	106	96
Related allowance	16	14
Consumer: \| 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	16	14
Amortized cost basis with allowance	53	51
Nonaccrual loans that are current	69	65
Related allowance	5	5
Consumer: \| Home equity credit line
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	0	0
Amortized cost basis with allowance	35	30
Nonaccrual loans that are current	35	30
Related allowance	9	8
Consumer: \| Bankcard and other revolving plans
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	0	0
Amortized cost basis with allowance	1	1
Nonaccrual loans that are current	1	1
Related allowance	1	$ 1
Consumer: \| Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortized cost basis with no allowance	0
Amortized cost basis with allowance	1
Nonaccrual loans that are current	1
Related allowance	$ 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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (cc)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3D
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3D

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3C

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

+ Details

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

- Definition

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477657/942-210-S45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478478/942-210-S50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(e)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestNonaccrual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestNonaccrualNoAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, Excluding Accrued Interest, Nonaccrual, Related Allowance

+ References

No definition available.

+ Details

Name:	zions_FinancingReceivableExcludingAccruedInterestNonaccrualRelatedAllowance
Namespace Prefix:	zions_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, Excluding Accrued Interest, Nonaccrual, With Allowance

+ References

No definition available.

+ Details

Name:	zions_FinancingReceivableExcludingAccruedInterestNonaccrualWithAllowance
Namespace Prefix:	zions_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_OwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_MunicipalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_TermMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_ConstructionAndLandDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_OneThroughFourFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_BankcardAndOtherRevolvingPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=zions_OtherConsumerLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: