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Commitments, Guarantees, And Contingent Liabilities (Schedule Of Guarantees Issued) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Liabilities for Guarantees on Long-Duration Contracts [Line Items]    
Commitments To Extend Credit $ 16,528,689zion_CommitmentsToExtendCredit $ 16,658,757zion_CommitmentsToExtendCredit
Commercial Letters Of Credit 68,807zion_CommercialLettersOfCredit 32,144zion_CommercialLettersOfCredit
Total Unfunded Lending Commitments 17,543,102zion_TotalUnfundedLendingCommitments 17,620,278zion_TotalUnfundedLendingCommitments
Financial [Member]    
Liabilities for Guarantees on Long-Duration Contracts [Line Items]    
Standby letters of credit 753,853zion_LettersOfCreditStandby
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_StandbyLettersOfCreditMember		 745,895zion_LettersOfCreditStandby
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_StandbyLettersOfCreditMember
Performance [Member]    
Liabilities for Guarantees on Long-Duration Contracts [Line Items]    
Standby letters of credit $ 191,753zion_LettersOfCreditStandby
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_PerformanceGuaranteeMember		 $ 183,482zion_LettersOfCreditStandby
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_PerformanceGuaranteeMember