2.4.0.84110 - Disclosure - Loans and Allowance for Loan Losses - Summary of Loans (Detail)truefalseIn Millions, unless otherwise specifiedfalse1false USDfalsefalse$I2013Q2http://www.sec.gov/CIK0001011659instant2013-06-30T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$I2012http://www.sec.gov/CIK0001011659instant2012-12-31T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 1us-gaap_ReceivablesAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Receivables [Abstract]2false 2us-gaap_LoansReceivableCommercialAndIndustrialus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse2226600000022266USD$falsetruefalse2truefalsefalse2082700000020827USD$falsetruefalsexbrli:monetaryItemTypemonetaryAmount before allowance of loans issued to commercial and industrial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes real estate loans and loans covered under loss sharing agreements.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5066-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph a -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(a)(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 false2Construction5false 2us-gaap_LeasesReceivableCommercialLeaseFinancingus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse984000000984falsefalsefalse2truefalsefalse11040000001104falsefalsefalsexbrli:monetaryItemTypemonetaryAmount before allowance of commercial leases and leveraged lease transactions where the entity is long-term creditor. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 6 -Subparagraph b(iii) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 47 -IssueDate 2006-05-01 -Chapter 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Lease financing6false 2us-gaap_LoansAndLeasesReceivableCommercialNetOfDeferredIncomeus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse3706600000037066falsefalsefalse2truefalsefalse3249700000032497falsefalsefalsexbrli:monetaryItemTypemonetaryReflects the net carrying amount of commercial loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on commercial loans and leases.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher OTS -Name Federal Regulation (FR) -Number Title 12 -Section 563c.102 -Paragraph 8 -Subparagraph e -Chapter V -Subsection I -LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 116 -IssueDate 2006-05-01 -Chapter 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. true2Total commercial portfolio7false 2ub_LoansAndLeasesReceivableResidentialMortgagesub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse2383500000023835falsefalsefalse2truefalsefalse2270500000022705falsefalsefalsexbrli:monetaryItemTypemonetaryLoans and leases receivable residential mortgages.No definition available.false2Residential mortgage8false 2ub_LoansAndLeasesReceivableHomeEquityAndOtherConsumerLoansub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse34560000003456falsefalsefalse2truefalsefalse36470000003647falsefalsefalsexbrli:monetaryItemTypemonetaryLoans and leases receivable, home equity and other consumer loans.No definition available.false2Home equity and other consumer loans9false 2us-gaap_LoansAndLeasesReceivableConsumerNetOfDeferredIncomeus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse2729100000027291falsefalsefalse2truefalsefalse2635200000026352falsefalsefalsexbrli:monetaryItemTypemonetaryReflects the net carrying amount of consumer loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on consumer loans and leases.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher OTS -Name Federal Regulation (FR) -Number Title 12 -Section 563c.102 -Paragraph 8 -Subparagraph e -Chapter V -Subsection I -LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 116 -IssueDate 2006-05-01 -Chapter 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. true2Total consumer portfolio10false 2us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse6435700000064357falsefalsefalse2truefalsefalse5884900000058849falsefalsefalsexbrli:monetaryItemTypemonetaryAmount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher OTS -Name Federal Regulation (FR) -Number Title 12 -Section 563c.102 -Paragraph 8 -Subparagraph e -Chapter V -Subsection I -LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 116 -IssueDate 2006-05-01 -Chapter 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. true2Total loans held for investment, before purchased credit-impaired loans11false 2ub_PurchasedCreditImpairedLoansub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse14860000001486falsefalsefalse2truefalsefalse11850000001185falsefalsefalsexbrli:monetaryItemTypemonetaryLoans acquired in a transfer, including business combinations, where there is evidence of credit deterioration since origination and it is probable at the date of acquisition that the Company will not collect all contractually required principal and interest payments are accounted for under accounting guidance for purchased credit-impaired loans. This guidance provides that the excess of the cash flows initially expected to be collected over the fair value of the loans at the acquisition date (i.e., the accretable yield) is accreted into interest income over the estimated remaining life of the purchased credit-impaired loans using the effective yield method, provided that the timing and amount of future cash flows is reasonably estimable. Accordingly, such loans are not classified as nonaccrual and are considered to be accruing because their interest income relates to the accretable yield recognized under accounting for purchased credit-impaired loans and not to contractual interest payments. The difference between the contractually required payments and the cash flows expected to be collected at acquisition, considering the impact of prepayments, is referred to as the nonaccretable difference.No definition available.false2Purchased credit-impaired loans12false 2ub_LoansIncludingPurchasedCreditImpairedLoansub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse6584300000065843falsefalsefalse2truefalsefalse6003400000060034falsefalsefalsexbrli:monetaryItemTypemonetaryAmount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans and leases covered under loss sharing agreements and acquired purchased credit-impaired loans.No definition available.true2Total loans held for investment13false 2ub_LoansAndLeasesReceivableAllowanceIncludingCreditImpairedLoansub_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse-625000000-625falsefalsefalse2truefalsefalse-653000000-653falsefalsefalsexbrli:monetaryItemTypemonetaryLoans and Leases Receivable Allowance Including Credit Impaired LoansNo definition available.false2Allowance for loan losses14false 2us-gaap_LoansAndLeasesReceivableNetReportedAmountCoveredAndNotCoveredus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse6521800000065218USD$falsetruefalse2truefalsefalse5938100000059381USD$falsetruefalsexbrli:monetaryItemTypemonetaryNet carrying amount of all categories of loans and leases held in portfolio, net of unearned income and the allowance for losses on loans and leases. Includes receivables covered through loss sharing agreements.No definition available.true2Loans held for investment, netfalseLoans and Allowance for Loan Losses - Summary of Loans (Detail) (USD $)MillionsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.unionbank.com/role/DisclosureLoansAndAllowanceForLoanLossesSummaryOfLoans214