2.4.0.84190 - Disclosure - Loans and Allowance for Loan Losses - Loans in Consumer Portfolio Segment Monitored for Credit Quality (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$1true 3ub_ScheduleOfFinancingReceivablesAccrualAndNonAccrualStatusLineItemsub_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Schedule Of Financing Receivables Accrual And Non Accrual Status [Line Items]2false 4ub_LoansAndLeasesReceivableResidentialMortgagesub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse2383500000023835USD$falsetruefalse2truefalsefalse2270500000022705USD$falsetruefalsexbrli:monetaryItemTypemonetaryLoans and leases receivable residential mortgages.No definition available.false2Total consumer portfolio3false 4ub_LoansAndLeasesReceivableHomeEquityAndOtherConsumerLoansub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse34560000003456USD$falsefalsefalse2truefalsefalse36470000003647USD$falsefalsefalsexbrli:monetaryItemTypemonetaryLoans and leases receivable, home equity and other consumer loans.No definition available.false2Total consumer portfolio4false 4ub_FinancingReceivableRecordedInvestmentNonaccrualsStatusub_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse520000000520USD$falsefalsefalse2truefalsefalse505000000505USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRecorded investment in financing receivable that are on nonaccrual status as of the balance sheet date.No definition available.false2Nonaccrual5false 4us-gaap_LoansAndLeasesReceivableConsumerNetOfDeferredIncomeus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse2729100000027291USD$falsefalsefalse2truefalsefalse2635200000026352USD$falsefalsefalsexbrli: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. 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