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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)(3)

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

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Commitments for Private Equity and Other Noninterest-bearing Investments

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Commitments for Private Equity or Other Non-Interest Bearing Investements Prohibited by the Volcker Rule

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Held-to-maturity securities, debt maturities, amortized cost.

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Held- to- maturity securities gross unrealized losses recognized in OCI.

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Held-To-Maturity Securities, Unrealized Losses OCI Reduction

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No definition available.

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Investment term of maturity.

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- Definition

Net Gains on Sales of CDOs

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Par Value of CDO Securities Sold

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- Definition

Private Equity Investments

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- Definition

Private equity investments prohibited by Volker rule

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Private Equity Investments Sold Prohibited by Volcker Rule

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Investment Securities (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended
Investment Securities (Narrative) (Details) (USD $)	Dec. 31, 2014 Securities	Mar. 31, 2015 Securities	Mar. 31, 2014	Mar. 31, 2015 Y
Investment [Line Items]
Held-to-maturity, Amortized cost	$ 686,951,000	$ 590,950,000		590,950,000
Private equity investments prohibited by Volker rule		33,000,000		33,000,000
Number of HTM investment securities in an unrealized loss position	153	188		188
Number of AFS investment securities in an unrealized loss position	458	433		433
Carrying value of pledged securities	1,400,000,000	1,300,000,000		1,300,000,000
Private Equity Investments		132,000,000zion_PrivateEquityInvestments		132,000,000zion_PrivateEquityInvestments
Par Value of CDO Securities Sold			993,000,000zion_ParValueofCDOSecuritiesSold
Net Gains on Sales of CDOs			31,000,000zion_NetGainsonSalesofCDOs
Held To Maturity Securities Gross Unrealized Losses	39,699,000
Held-To-Maturity Securities, Unrealized Losses OCI Reduction		18,000,000
Private Equity Investments Sold Prohibited by Volcker Rule	8,000,000	5,000,000		5,000,000
Commitments for Private Equity and Other Noninterest-bearing Investments		34,900,000		34,900,000
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule		8,000,000		8,000,000
U.S. Treasury, Agencies And Corporations [Member] \| Minimum [Member]
Investment [Line Items]
Investment term of maturity				1
U.S. Treasury, Agencies And Corporations [Member] \| Maximum [Member]
Investment [Line Items]
Investment term of maturity				25
Small Business Administration Loan-Backed Securities [Member] \| Minimum [Member]
Investment [Line Items]
Investment term of maturity				5
Small Business Administration Loan-Backed Securities [Member] \| Maximum [Member]
Investment [Line Items]
Investment term of maturity				25
Municipal Securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost	607,675,000	590,950,000		590,950,000
Held To Maturity Securities Gross Unrealized Losses	0
Asset-backed Securities [Member] \| Trust Preferred Securities - Banks And Insurance [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost	79,276,000
Held To Maturity Securities Gross Unrealized Losses	$ 39,699,000