Derivative Instruments and Hedging Activities (Derivative Gain (Loss) Recognized/Reclassified) (Details) - USD ($)	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) reclassified from AOCI into income	$ (26,000,000)	$ (37,000,000)
Loss to be reclassified within the next 12 months into interest income	102,000,000	156,000,000
Derivatives designated as hedging instruments:
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain/(loss) deferred in AOCI	(1,000,000)	38,000,000
Amount of gain/(loss) reclassified from AOCI into income	(34,000,000)	(49,000,000)
Interest on fair value hedges	21,000,000	10,000,000
Derivatives designated as hedging instruments: \| Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Terminated or redesignated, unamortized basis adjustments, debt	45,000,000	0
Terminated or redesignated, unamortized basis adjustments, assets	3,000,000	10,000,000
Derivatives designated as hedging instruments: \| Cash Flow Hedging \| Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain/(loss) deferred in AOCI	(5,000,000)	38,000,000
Amount of gain/(loss) reclassified from AOCI into income	(36,000,000)	(49,000,000)
Interest on fair value hedges	0	0
Derivatives designated as hedging instruments: \| Fair Value Hedging \| Pay-fixed interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain/(loss) deferred in AOCI	4,000,000	0
Amount of gain/(loss) reclassified from AOCI into income	2,000,000	0
Interest on fair value hedges	0	0
Derivatives designated as hedging instruments: \| Fair Value Hedging \| Debt hedges: Receive-fixed interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain/(loss) deferred in AOCI	0	0
Amount of gain/(loss) reclassified from AOCI into income	0	0
Interest on fair value hedges	(2,000,000)	4,000,000
Derivatives designated as hedging instruments: \| Fair Value Hedging \| Asset hedges: Pay-fixed interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain/(loss) deferred in AOCI	0	0
Amount of gain/(loss) reclassified from AOCI into income	0	0
Interest on fair value hedges	$ 23,000,000	$ 6,000,000

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480870/815-30-50-1

+ Details

Name:	us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4E
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4E

+ Details

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

- Definition

Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4C

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480627/815-20-45-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4A

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Derivative instrument noninterest income (expense)

+ References

No definition available.

+ Details

Name:	zions_DerivativeInstrumentNoninterestIncomeExpense
Namespace Prefix:	zions_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Terminated And Redesignated Swaps, Unamortized Basis Adjustments, Assets

+ References

No definition available.

+ Details

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

- Definition

Terminated And Redesignated Swaps, Unamortized Basis Adjustments, Debt

+ References

No definition available.

+ Details

Name:	zions_TerminatedAndRedesignatedSwapsUnamortizedBasisAdjustmentsDebt
Namespace Prefix:	zions_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=zions_DebtHedgesReceivedFixedInterestRateSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=zions_AssetHedgePayFixedInterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: