3.8.0.1 html 702 383 1 true 121 0 false 7 false false R1.htm 0001000 - Document - Document And Entity Information Sheet http://www.comerica.com/role/DocumentAndEntityInformation Document And Entity Information Cover 1 false false R2.htm 1001000 - Statement - Consolidated Balance Sheets Sheet http://www.comerica.com/role/ConsolidatedBalanceSheets Consolidated Balance Sheets Statements 2 false false R3.htm 1001501 - Statement - Consolidated Balance Sheets (Parenthetical) Sheet http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 1002000 - Statement - Consolidated Statements Of Comprehensive Income Sheet http://www.comerica.com/role/ConsolidatedStatementsOfComprehensiveIncome Consolidated Statements Of Comprehensive Income Statements 4 false false R5.htm 1004000 - Statement - Consolidated Statements Of Changes In Shareholders' Equity Sheet http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity Consolidated Statements Of Changes In Shareholders' Equity Statements 5 false false R6.htm 1004001 - Statement - Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical) Sheet http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquityParenthetical Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical) Statements 6 false false R7.htm 1005000 - Statement - Consolidated Statements Of Cash Flows Sheet http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows Consolidated Statements Of Cash Flows Statements 7 false false R8.htm 2101100 - Disclosure - Basis of Presentation and Accounting Policies Sheet http://www.comerica.com/role/BasisOfPresentationAndAccountingPolicies Basis of Presentation and Accounting Policies Notes 8 false false R9.htm 2102100 - Disclosure - Fair Value Measurements Sheet http://www.comerica.com/role/FairValueMeasurements Fair Value Measurements Notes 9 false false R10.htm 2103100 - Disclosure - Investment Securities Sheet http://www.comerica.com/role/InvestmentSecurities Investment Securities Notes 10 false false R11.htm 2104100 - Disclosure - Credit Quality And Allowance For Credit Losses Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLosses Credit Quality And Allowance For Credit Losses Notes 11 false false R12.htm 2109100 - Disclosure - Derivative And Credit-Related Financial Instruments Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstruments Derivative And Credit-Related Financial Instruments Notes 12 false false R13.htm 2110100 - Disclosure - Variable Interest Entities (VIEs) Sheet http://www.comerica.com/role/VariableInterestEntitiesVies Variable Interest Entities (VIEs) Notes 13 false false R14.htm 2113100 - Disclosure - Medium- And Long-Term Debt Sheet http://www.comerica.com/role/MediumAndLongTermDebt Medium- And Long-Term Debt Notes 14 false false R15.htm 2115100 - Disclosure - Accumulated Other Comprehensive Loss Sheet http://www.comerica.com/role/AccumulatedOtherComprehensiveLoss Accumulated Other Comprehensive Loss Notes 15 false false R16.htm 2116100 - Disclosure - Net Income Per Common Share Sheet http://www.comerica.com/role/NetIncomePerCommonShare Net Income Per Common Share Notes 16 false false R17.htm 2118100 - Disclosure - Employee Benefit Plans Sheet http://www.comerica.com/role/EmployeeBenefitPlans Employee Benefit Plans Notes 17 false false R18.htm 2120100 - Disclosure - Income Taxes And Tax-Related Items Sheet http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItems Income Taxes And Tax-Related Items Notes 18 false false R19.htm 2123100 - Disclosure - Contingent Liabilities Sheet http://www.comerica.com/role/ContingentLiabilities Contingent Liabilities Notes 19 false false R20.htm 2125100 - Disclosure - Restructuring Charges Sheet http://www.comerica.com/role/RestructuringCharges Restructuring Charges Notes 20 false false R21.htm 2126100 - Disclosure - Business Segment Information Sheet http://www.comerica.com/role/BusinessSegmentInformation Business Segment Information Notes 21 false false R22.htm 2127100 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts with Customers Sheet http://www.comerica.com/role/RevenueFromContractsWithCustomersRevenueFromContractsWithCustomers Revenue from Contracts with Customers Revenue from Contracts with Customers Notes 22 false false R23.htm 2201201 - Disclosure - Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies) Sheet http://www.comerica.com/role/BasisOfPresentationAndAccountingPoliciesBasisOfPresentationAndAccountingPoliciesPolicies Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies) Policies http://www.comerica.com/role/BasisOfPresentationAndAccountingPolicies 23 false false R24.htm 2302301 - Disclosure - Fair Value Measurements (Tables) Sheet http://www.comerica.com/role/FairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://www.comerica.com/role/FairValueMeasurements 24 false false R25.htm 2303301 - Disclosure - Investment Securities (Tables) Sheet http://www.comerica.com/role/InvestmentSecuritiesTables Investment Securities (Tables) Tables http://www.comerica.com/role/InvestmentSecurities 25 false false R26.htm 2304301 - Disclosure - Credit Quality And Allowance For Credit Losses (Tables) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables Credit Quality And Allowance For Credit Losses (Tables) Tables http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLosses 26 false false R27.htm 2309301 - Disclosure - Derivative And Credit-Related Financial Instruments (Tables) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables Derivative And Credit-Related Financial Instruments (Tables) Tables http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstruments 27 false false R28.htm 2310301 - Disclosure - Variable Interest Entities (VIEs) (Tables) Sheet http://www.comerica.com/role/VariableInterestEntitiesViesTables Variable Interest Entities (VIEs) (Tables) Tables http://www.comerica.com/role/VariableInterestEntitiesVies 28 false false R29.htm 2313301 - Disclosure - Medium- And Long-Term Debt (Tables) Sheet http://www.comerica.com/role/MediumAndLongTermDebtTables Medium- And Long-Term Debt (Tables) Tables http://www.comerica.com/role/MediumAndLongTermDebt 29 false false R30.htm 2315301 - Disclosure - Accumulated Other Comprehensive Loss (Tables) Sheet http://www.comerica.com/role/AccumulatedOtherComprehensiveLossTables Accumulated Other Comprehensive Loss (Tables) Tables http://www.comerica.com/role/AccumulatedOtherComprehensiveLoss 30 false false R31.htm 2316301 - Disclosure - Net Income Per Common Share (Tables) Sheet http://www.comerica.com/role/NetIncomePerCommonShareTables Net Income Per Common Share (Tables) Tables http://www.comerica.com/role/NetIncomePerCommonShare 31 false false R32.htm 2318301 - Disclosure - Employee Benefit Plans (Tables) Sheet http://www.comerica.com/role/EmployeeBenefitPlansTables Employee Benefit Plans (Tables) Tables http://www.comerica.com/role/EmployeeBenefitPlans 32 false false R33.htm 2325301 - Disclosure - Restructuring Charges (Tables) Sheet http://www.comerica.com/role/RestructuringChargesTables Restructuring Charges (Tables) Tables http://www.comerica.com/role/RestructuringCharges 33 false false R34.htm 2326301 - Disclosure - Business Segment Information (Tables) Sheet http://www.comerica.com/role/BusinessSegmentInformationTables Business Segment Information (Tables) Tables http://www.comerica.com/role/BusinessSegmentInformation 34 false false R35.htm 2327301 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts with Customers (Tables) Sheet http://www.comerica.com/role/RevenueFromContractsWithCustomersRevenueFromContractsWithCustomersTables Revenue from Contracts with Customers Revenue from Contracts with Customers (Tables) Tables http://www.comerica.com/role/RevenueFromContractsWithCustomersRevenueFromContractsWithCustomers 35 false false R36.htm 2401402 - Disclosure - Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) Sheet http://www.comerica.com/role/BasisOfPresentationAndAccountingPoliciesBasisOfPresentationAndAccountingPoliciesNarrativeDetails Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details) Details http://www.comerica.com/role/BasisOfPresentationAndAccountingPoliciesBasisOfPresentationAndAccountingPoliciesPolicies 36 false false R37.htm 2402402 - Disclosure - Fair Value Measurements (Narrative) (Details) Sheet http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails Fair Value Measurements (Narrative) (Details) Details http://www.comerica.com/role/FairValueMeasurementsTables 37 false false R38.htm 2402403 - Disclosure - Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Recurring Basis) (Details) Sheet http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnRecurringBasisDetails Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Recurring Basis) (Details) Details http://www.comerica.com/role/FairValueMeasurementsTables 38 false false R39.htm 2402404 - Disclosure - Fair Value Measurements (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) Sheet http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails Fair Value Measurements (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) Details http://www.comerica.com/role/FairValueMeasurementsTables 39 false false R40.htm 2402405 - Disclosure - Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details) Sheet http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnNonrecurringBasisDetails Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details) Details http://www.comerica.com/role/FairValueMeasurementsTables 40 false false R41.htm 2402406 - Disclosure - Fair Value Measurements (Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis) (Details) Sheet http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnRecurringBasisDetails Fair Value Measurements (Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis) (Details) Details http://www.comerica.com/role/FairValueMeasurementsTables 41 false false R42.htm 2403402 - Disclosure - Investment Securities (Narrative) (Details) Sheet http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails Investment Securities (Narrative) (Details) Details http://www.comerica.com/role/InvestmentSecuritiesTables 42 false false R43.htm 2403403 - Disclosure - Investment Securities (Summary Of Investment Securities Available-For-Sale) (Details) Sheet http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesAvailableForSaleDetails Investment Securities (Summary Of Investment Securities Available-For-Sale) (Details) Details http://www.comerica.com/role/InvestmentSecuritiesTables 43 false false R44.htm 2403404 - Disclosure - Investment Securities (Summary Of Investment Securities Available-For-Sale In Unrealized Loss Positions) (Details) Sheet http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesAvailableForSaleInUnrealizedLossPositionsDetails Investment Securities (Summary Of Investment Securities Available-For-Sale In Unrealized Loss Positions) (Details) Details http://www.comerica.com/role/InvestmentSecuritiesTables 44 false false R45.htm 2403405 - Disclosure - Investment Securities (Contractual Maturity Distribution Of Debt Securities) (Details) Sheet http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails Investment Securities (Contractual Maturity Distribution Of Debt Securities) (Details) Details http://www.comerica.com/role/InvestmentSecuritiesTables 45 false false R46.htm 2404402 - Disclosure - Credit Quality And Allowance For Credit Losses (Narrative) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails Credit Quality And Allowance For Credit Losses (Narrative) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 46 false false R47.htm 2404403 - Disclosure - Credit Quality And Allowance For Credit Losses (Aging Analysis Of Loans) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails Credit Quality And Allowance For Credit Losses (Aging Analysis Of Loans) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 47 false false R48.htm 2404404 - Disclosure - Credit Quality And Allowance For Credit Losses (Loans By Credit Quality Indicator) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorDetails Credit Quality And Allowance For Credit Losses (Loans By Credit Quality Indicator) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 48 false false R49.htm 2404405 - Disclosure - Credit Quality And Allowance For Credit Losses (Schedule Of Nonaccrual, Reduced-Rate Loans And Foreclosed Property) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesScheduleOfNonaccrualReducedRateLoansAndForeclosedPropertyDetails Credit Quality And Allowance For Credit Losses (Schedule Of Nonaccrual, Reduced-Rate Loans And Foreclosed Property) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 49 false false R50.htm 2404406 - Disclosure - Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Loan Losses And Related Loan Amounts) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInAllowanceForLoanLossesAndRelatedLoanAmountsDetails Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Loan Losses And Related Loan Amounts) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 50 false false R51.htm 2404407 - Disclosure - Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Credit Losses On Lending-Related Commitments) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInAllowanceForCreditLossesOnLendingRelatedCommitmentsDetails Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Credit Losses On Lending-Related Commitments) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 51 false false R52.htm 2404408 - Disclosure - Credit Quality And Allowance For Credit Losses (Individually Evaluated Impaired Loans) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesIndividuallyEvaluatedImpairedLoansDetails Credit Quality And Allowance For Credit Losses (Individually Evaluated Impaired Loans) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 52 false false R53.htm 2404409 - Disclosure - Credit Quality And Allowance For Credit Losses (Average Individually Evaluated Impaired Loans And Related Interest Recognized) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAverageIndividuallyEvaluatedImpairedLoansAndRelatedInterestRecognizedDetails Credit Quality And Allowance For Credit Losses (Average Individually Evaluated Impaired Loans And Related Interest Recognized) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 53 false false R54.htm 2404410 - Disclosure - Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings By Type Of Modification) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsByTypeOfModificationDetails Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings By Type Of Modification) (Details) Details http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables 54 false false R55.htm 2404411 - Disclosure - Credit Quality And Allowance For Credit Losses Credit Quality And Allowance For Credit Losses (Troubled Debt Restructuring Subsequent Default) (Details) Sheet http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesCreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringSubsequentDefaultDetails Credit Quality And Allowance For Credit Losses Credit Quality And Allowance For Credit Losses (Troubled Debt Restructuring Subsequent Default) (Details) Details 55 false false R56.htm 2409402 - Disclosure - Derivative And Credit-Related Financial Instruments (Narrative) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails Derivative And Credit-Related Financial Instruments (Narrative) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 56 false false R57.htm 2409403 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Derivative Instruments) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails Derivative And Credit-Related Financial Instruments (Schedule Of Derivative Instruments) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 57 false false R58.htm 2409404 - Disclosure - Derivative And Credit-Related Financial Instruments Derivative and Credit-Related Financial Instruments (Schedule of the Effects of Fair Value Hedging on the Consolidated Statements of Comprehensive Income (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleOfEffectsOfFairValueHedgingOnConsolidatedStatementsOfComprehensiveIncomeDetails Derivative And Credit-Related Financial Instruments Derivative and Credit-Related Financial Instruments (Schedule of the Effects of Fair Value Hedging on the Consolidated Statements of Comprehensive Income (Details) Details 58 false false R59.htm 2409405 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementInterestRateSwapsDetails Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 59 false false R60.htm 2409406 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails Derivative And Credit-Related Financial Instruments (Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 60 false false R61.htm 2409407 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails Derivative And Credit-Related Financial Instruments (Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 61 false false R62.htm 2409408 - Disclosure - Derivative And Credit-Related Financial Instruments (Summary Of Internally Classified Watch List Letters Of Credit) (Details) Sheet http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsSummaryOfInternallyClassifiedWatchListLettersOfCreditDetails Derivative And Credit-Related Financial Instruments (Summary Of Internally Classified Watch List Letters Of Credit) (Details) Details http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables 62 false false R63.htm 2410402 - Disclosure - Variable Interest Entities (VIEs) (Narrative) (Details) Sheet http://www.comerica.com/role/VariableInterestEntitiesViesNarrativeDetails Variable Interest Entities (VIEs) (Narrative) (Details) Details http://www.comerica.com/role/VariableInterestEntitiesViesTables 63 false false R64.htm 2410403 - Disclosure - Variable Interest Entities (VIEs) (Impact Of VIEs On The Consolidated Statements Of Comprehensive Income) (Details) Sheet http://www.comerica.com/role/VariableInterestEntitiesViesImpactOfViesOnConsolidatedStatementsOfComprehensiveIncomeDetails Variable Interest Entities (VIEs) (Impact Of VIEs On The Consolidated Statements Of Comprehensive Income) (Details) Details http://www.comerica.com/role/VariableInterestEntitiesViesTables 64 false false R65.htm 2413402 - Disclosure - Medium- And Long-Term Debt (Narrative) (Details) Sheet http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails Medium- And Long-Term Debt (Narrative) (Details) Details http://www.comerica.com/role/MediumAndLongTermDebtTables 65 false false R66.htm 2413403 - Disclosure - Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details) Sheet http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details) Details http://www.comerica.com/role/MediumAndLongTermDebtTables 66 false false R67.htm 2415402 - Disclosure - Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Loss) (Details) Sheet http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveLossDetails Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Loss) (Details) Details http://www.comerica.com/role/AccumulatedOtherComprehensiveLossTables 67 false false R68.htm 2416402 - Disclosure - Net Income Per Common Share (Narrative) Sheet http://www.comerica.com/role/NetIncomePerCommonShareNarrative Net Income Per Common Share (Narrative) Uncategorized 68 false false R69.htm 2416403 - Disclosure - Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details) Sheet http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details) Uncategorized 69 false false R70.htm 2418402 - Disclosure - Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) Sheet http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) Uncategorized 70 false false R71.htm 2420401 - Disclosure - Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Narrative) (Details) Sheet http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Narrative) (Details) Uncategorized 71 false false R72.htm 2423401 - Disclosure - Contingent Liabilities (Narrative) (Details) Sheet http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails Contingent Liabilities (Narrative) (Details) Uncategorized 72 false false R73.htm 2425402 - Disclosure - Restructuring Charges (Narrative) (Details) Sheet http://www.comerica.com/role/RestructuringChargesNarrativeDetails Restructuring Charges (Narrative) (Details) Uncategorized 73 false false R74.htm 2425403 - Disclosure - Restructuring Charges (Schedule of Changes in Restructuring Reserves) (Details) Sheet http://www.comerica.com/role/RestructuringChargesScheduleOfChangesInRestructuringReservesDetails Restructuring Charges (Schedule of Changes in Restructuring Reserves) (Details) Uncategorized 74 false false R75.htm 2426402 - Disclosure - Business Segment Information (Narrative) (Details) Sheet http://www.comerica.com/role/BusinessSegmentInformationNarrativeDetails Business Segment Information (Narrative) (Details) Uncategorized 75 false false R76.htm 2426403 - Disclosure - Business Segment Information (Business Segment Financial Results) (Details) Sheet http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails Business Segment Information (Business Segment Financial Results) (Details) Uncategorized 76 false false R77.htm 2426404 - Disclosure - Business Segment Information (Market Segment Financial Results) (Details) Sheet http://www.comerica.com/role/BusinessSegmentInformationMarketSegmentFinancialResultsDetails Business Segment Information (Market Segment Financial Results) (Details) Uncategorized 77 false false R78.htm 2427402 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts with Customers (Details) Sheet http://www.comerica.com/role/RevenueFromContractsWithCustomersRevenueFromContractsWithCustomersDetails Revenue from Contracts with Customers Revenue from Contracts with Customers (Details) Uncategorized 78 false false All Reports Book All Reports cma-20180331.xml cma-20180331.xsd cma-20180331_cal.xml cma-20180331_def.xml cma-20180331_lab.xml cma-20180331_pre.xml http://xbrl.sec.gov/invest/2013-01-31 http://fasb.org/us-gaap/2017-01-31 http://xbrl.sec.gov/dei/2014-01-31 http://xbrl.sec.gov/stpr/2011-01-31 true true