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Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Proceeds from sales of premises and equipment Proceeds from Sale of Property, Plant, and Equipment Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Amortization of mortgage servicing rights Amortization of Mortgage Servicing Rights (MSRs) Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Schedule of Income Taxes Paid, Net of Refunds Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Total interest expense Interest Expense, Operating Net unrecognized prior service credit Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Due in one year or less Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Year One INCOME (LOSS) FROM CONTINUING OPERATIONS Income (loss) from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Schedule of Weighted-Average Rates to Determine Actuarial Present Value of Benefit Obligations Weighted Average Rates To Determine Actuarial Present Value Of Benefit Obligations [Table Text Block] Weighted Average Rates To Determine Actuarial Present Value Of Benefit Obligations [Text Block] Derivative assets before collateral Derivative Assets Before Cash Collateral Derivative assets before cash collateral. 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Schedule of Details of Securities Marketable Securities [Table Text Block] Gross Unrealized Losses Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss Accrued income and other assets Other Assets, Fair Value Disclosure Federal Reserve Bank of Cleveland Federal Reserve Bank Of Cleveland [Member] Federal Reserve Bank Of Cleveland [Member] NONINTEREST EXPENSE Noninterest Expense [Abstract] Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Cash and due from banks Cash and Due from Banks OTHER FINANCIAL DATA Other Financial Data [Abstract] Other financial data. Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Noncurrent assets Assets for Plan Benefits, Defined Benefit Plan Currently payable: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis Fair Value Assets And Liabilities Measured On Recurring Basis [Table Text Block] Fair Value Assets And Liabilities Measured On Recurring Basis Issuance of common shares (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Shares Issued in Period Liability Recorded Guarantor Obligations, Current Carrying Value Schedule of Finite-Lived Intangible Assets, Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Due after one through five years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Amount of offset in excess of securities collateral held Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Securities Collateral Held Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Securities Collateral Held Weighted-average Interest Rate Change Financing Receivable, Modified, Weighted Average Interest Rate Decrease from Modification Number of Nonvested Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] First Niagara Bank, N.A. First Niagara Bank, N.A. [Member] First Niagara Bank, N.A. [Member] Pledged Status [Domain] Pledged Status [Domain] Commercial and Industrial Commercial And Industrial [Member] Commercial and Industrial Entity Address, Postal Zip Code Entity Address, Postal Zip Code Income taxes Total income tax expense (benefit) Income taxes Income tax (expense) benefit Income Tax Expense (Benefit) Income (loss) from discontinued operations, net of taxes (in dollars per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Accrued income and other assets Other Assets Government National Mortgage Association (GNMA) Government National Mortgage Association (GNMA) [Member] All subsequent years Time Deposit Maturities, after Year Five Designated as Hedging Instrument Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Hedging Relationship [Axis] Hedging Relationship [Axis] Premises and equipment Property, Plant and Equipment, Gross Cash and short-term investments Cash, Cash Equivalents, and Short-Term Investments Due in one year or less Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Low-income housing/New markets Effective Income Tax Rate Reconciliation, Tax Credit, Low-Income Housing And New Markets, Percent Effective Income Tax Rate Reconciliation, Tax Credit, Low-Income Housing And New Markets, Percent Unpaid principal balance outstanding of loans sold Recorded Unconditional Purchase Obligation Schedule of Plans ABO in Excess of Plan Assets Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Table Text Block] Discontinued Operations and Disposal Groups [Abstract] Discontinued Operations and Disposal Groups [Abstract] Principal investments: Indirect Indirect investments Principal Indirect Investments [Member] Principal indirect investments. Guarantor Obligation [Table] Guarantor Obligation [Table] Federal Home Loan Bank Branch [Domain] Federal Home Loan Bank Branch [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Cash received from options exercised Proceeds from Stock Options Exercised Less: Accumulated depreciation and amortization Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, Accumulated Depreciation and Amortization U.S. Federal Income Tax Paid, Federal, after Refund Received Buildings and improvements Building and Building Improvements [Member] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] Weighted-average remaining life, exercisable Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Tax-exempt interest income Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent ABO Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation Outstanding, beginning balance (in shares) Outstanding, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Mortgage Servicing Assets Mortgage Servicing Assets [Text Block] Mortgage servicing assets. Income (loss) before equity in net income (loss) less dividends from subsidiaries Income Loss before Equity in Net Income Loss Less Dividends from Subsidiaries Income Loss before Equity in Net Income Loss Less Dividends from Subsidiaries NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Escrow earn rate assumptions Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Escrow Earn Rate Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Escrow Earn Rate Securities related to purchase of senior notes Debt Securities, Held-To-Maturity, Purchase of Senior Notes Debt Securities, Held-To-Maturity, Purchase of Senior Notes Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Proceeds from sales of securities available for sale Proceeds from Sale of Debt Securities, Available-for-Sale Securities available for sale Fair Value Total Debt Securities, Available-for-Sale, Excluding Accrued Interest Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Useful life (in years) Property, Plant and Equipment, Useful Life Schedule of Assumptions Used in Options Pricing Model Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Recoveries Financing Receivable, Allowance for Credit Loss, Recovery NET INTEREST INCOME Interest Income (Expense), Operating Tier 1 risk- based capital, actual amount Banking Regulation, Tier 1 Risk-Based Capital, Actual Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Schedule of Commitments to Extend Credit or Funding Schedule Of Contractual Amounts Of Unused Lending Commitments To Extend Credit Table [Table Text Block] Schedule Of Contractual Amounts Of Unused Lending Commitments To Extend Credit Table [Text Block] Loans transferred to portfolio from held for sale Loan, Transfer from Held-for-Sale to Held-in-Portfolio Derivative liabilities Derivative liabilities, fair value Derivative Liability, Subject to Master Netting Arrangement, before Offset Equity Components [Axis] Equity Components [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Year four Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year Consumer mortgage income Consumer Mortgage Income [Member] Consumer Mortgage Income [Member] Number of reportable business segments Number of Reportable Segments Servicing Asset [Abstract] Servicing Asset [Abstract] Total commercial real estate loans Total commercial real estate loans Commercial Real Estate [Member] Common Shares reissued under Scotiabank investment agreement, net of issuance costs Stock Issued During Period, Value, Treasury Stock Reissued Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Entity Address, State or Province Entity Address, State or Province Thereafter Sales-Type and Direct Financing Leases, Payment to be Received, after Year Five Total interest income Interest and Dividend Income, Operating Financial Asset, Period Past Due [Domain] Financial Asset, Aging [Domain] Financial Asset, Aging [Domain] 2029 Defined Benefit Plan, Expected Future Benefit Payment, Year Four Unused secured borrowing capacity Debt Instrument, Unused Borrowing Capacity, Amount Temporarily impaired securities, gross unrealized losses Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position Aggregate Losses Available for sale and held to maturity securities continuous unrealized loss position aggregate losses. Payment / Performance Risk Credit Derivative Payment Performance Risk Percentage Credit derivative payment performance risk percentage. Vesting period Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Periods Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Periods Total expenses associated with saving plan Defined Contribution Plan, Cost Total premises and equipment Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, before Accumulated Depreciation and Amortization Operating lease payments Lessor, Operating Lease, Payment to be Received, Fiscal Year Maturity [Abstract] Income Tax Jurisdiction [Domain] Income Tax Jurisdiction [Domain] Entities [Table] Entities [Table] Amortization of investment Amortization Number of loan modifications Financing Receivable, Modifications, Number of Loans Financing Receivable, Modifications, Number of Loans Settlement loss Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement Balance at beginning of period Balance at end of period Servicing Asset at Amortized Cost Maximum Exposure to Loss Maximum Exposure To Loss Unconsolidated Vie Maximum exposure to loss unconsolidated VIE. 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Modified [Line Items] Funded status Defined Benefit Plan, Funded (Unfunded) Status of Plan INTEREST INCOME INCOME Interest and Dividend Income, Operating [Abstract] Expected to vest, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Share-based compensation expense Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-Based Payment Arrangement, Amount Total noninterest expense Noninterest Expense Schedule of Activity, Pricing and Other Information for Stock Options Disclosure of Share-Based Compensation Arrangements by Share-Based Payment Award [Table Text Block] Equity and gross receipts based taxes assessed in lieu of income tax recorded in noninterest expense Taxes In Lieu Of Income Tax Taxes In Lieu Of Income Tax Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Deposits Interest Expense, Deposits Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] NONINTEREST INCOME Noninterest Income [Abstract] Schedule of Minimum Future Lease Payments to be Received for Operating Leases Lessor, Operating Lease, Payment to be Received, Maturity [Table Text Block] Series D Preferred Stock Series D Preferred Stock [Member] Exercise rate of stock options granted to employees Share Based Compensation Arrangement By Share Based Payment Award, Vesting Percentage Of Stock Options Granted To Employees Other Than Executive Officers Share Based Compensation Arrangement By Share Based Payment Award, Vesting Percentage Of Stock Options Granted To Employees Other Than Executive Officers 2027 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Condensed Financial Statements [Table] Condensed Financial Statements [Table] Other consumer loans Other Consumer Loans [Member] Other Consumer Loans Entity Central Index Key Entity Central Index Key Schedule of Changes in Liability for Credit Losses on Off-Balance Sheet Exposures Financing Receivables, 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forecasted transactions are hedged, years Maximum Length Of Time Over Which Forecasted Transactions Are Hedged Maximum length of time over which forecasted transactions are hedged. Gross Carrying Amount Finite-Lived Intangible Assets, Gross Purchases Servicing Asset at Amortized Cost, Additions Temporarily impaired securities, gross unrealized losses, less than 12 months Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses Available for sale and held to maturity securities continuous unrealized loss position less than twelve months aggregate losses. Number of state branch footprint Number of States in which Entity Operates Entity Address, Address Line One Entity Address, Address Line One Effect on fair value from 20% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Other than 10 or 20 Percent Adverse Change in Prepayment Speed Accumulated Other Comprehensive Income (Loss) Total AOCI Attributable to Parent [Member] Liability for estimated repurchase obligations on loans sold Assets Sold under Agreements to Repurchase, Repurchase Liability Investments [Domain] Investments [Domain] Current period gross write-offs, Revolving Loans Converted to Term Loans Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Off-Balance-Sheet, Credit Loss, Liability [Roll Forward] Off-Balance-Sheet, Credit Loss, Liability [Roll Forward] Internal Credit 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Loans transferred to held for sale from portfolio Loan and Lease, Transfer from Held-in-Portfolio to Held-for-Sale Deposits with the federal reserve Cash Reserve Deposited At Federal Reserve Bank Cash Reserve Deposited At Federal Reserve Bank Schedule of Changes in Carrying Amount of Goodwill Schedule of Goodwill [Table Text Block] Operating lease income and other leasing gains Total operating lease income and other leasing gains Operating Lease, Lease Income Net unrecognized losses (gains) Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Series E Preferred Stock Series E Preferred Stock [Member] Security Exchange Name Security Exchange Name Total lease income Lease Income Other Defined Benefit Plans Other Pension Plan [Member] 30-89 Days Past Due Financial Asset, 30 To 89 Days Past Due [Member] Financial Asset, 30 To 89 Days Past Due Proceeds from sales of portfolio loans Proceeds from Sale, Loan, Held-for-Investment 2027 Lessor, Operating Lease, Payment to be Received, Year Two Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Loans held for sale Interest and Fee Income, Loan and Lease, Held-for-Sale Asset Quality Financing Receivables [Text Block] Capitalized computer software Capitalized Computer Software, Net Less: Dividends on preferred stock Dividends, Preferred Stock Temporarily impaired securities, fair value Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position Fair Value Available for sale and held to maturity securities continuous unrealized loss position fair value. Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Other assets (measured at NAV) Defined Benefit Plan, Other Assets [Member] Defined Benefit Plan, Other Assets [Member] Pledging Purpose [Axis] Pledging Purpose [Axis] Employee equity compensation program Common Share repurchases (in shares) Stock Repurchased During Period, Shares Income (loss) from continuing operations attributable to Key common shareholders (in dollars per share) Income Loss From Continuing Operations Attributable To Commons Shareholders Per Basic Share The amount of income (loss) from continuing operations after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period) per each share of common stock outstanding during the reporting period. Tier 1 risk based capital leverage, regulatory minimum with stress capital buffer Banking Regulation, Supplementary Leverage Ratio, Undercapitalized, Minimum Plan participants’ contributions Defined Benefit Plan, Plan Assets, Contributions by Plan Participant Asset Class [Domain] Asset Class [Domain] Discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Total trading account assets Trading Accounts Asset Trading Accounts Asset Equity Investments, Direct, NAV Equity Investments Direct, NAV [Member] Equity Investments Direct, NAV [Member] Noncurrent liabilities Liability, Defined Benefit Plan, Noncurrent Statement [Line Items] Statement [Line Items] Subordinated Notes Due 2026- 2032 Subordinated Notes Due 2026- 2032 [Member] Subordinated Notes Due 2026- 2032 Increase in number of shares that may be issued as equity awards (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized Consumer Bank Consumer Bank [Member] Consumer Bank [Member] Deferred income taxes (benefit) Increase (Decrease) in Deferred Income Taxes Common Shares Common Stock [Member] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Other Variable Rate Notes Other Variable Rate Notes [Member] Other Variable Rate Notes Due 2025 Other short-term borrowings Other Short-Term Borrowings NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Federal funds purchased Federal Funds Purchased Statistical Measurement [Domain] Statistical Measurement [Domain] NMTC NMTC [Member] NMTC Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Schedule of Condensed Balance Sheets Condensed Balance Sheet [Table Text Block] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Short-term borrowings Short-Term Debt, Fair Value Equity Investments Equity Investments [Member] Equity Investments [Member] Asset Class [Axis] Asset Class [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Real estate — commercial mortgage Commercial Real Estate Commercial Mortgage [Member] Commercial real estate commercial mortgage. Corporate-owned life insurance Bank Owned Life Insurance Equity in net income (loss) less dividends from subsidiaries Equity in net (income) loss less dividends from subsidiaries Income (Loss) from Equity Method Investments Leases [Abstract] Leases [Abstract] Junior subordinated debentures Subordinated Long-Term Debt, Noncurrent Increase for other tax positions of prior years Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Fair value, total Debt Securities, Held-to-Maturity, Unrealized Loss Position, Fair Value Percentage of carrying amount of our commercial nonperforming loans outstanding Percentage Of Carrying Amount Of Our Commercial Nonperforming Loans Outstanding Percentage of carrying amount of our commercial nonperforming loans outstanding. 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Also includes a roll-forward of the allowance for loan losses, a roll-forward for liability for credit losses on lending-related commitments, composition of the net investment in direct financing leases and minimum future lease payments receivables as well as the related allowance. Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Prepayment rate Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed Schedule of Selected Financial Data for Our Business Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Income (loss) from discontinued operations, net of taxes (in dollars per share) Income (loss) from discontinued operations, net of taxes — assuming dilution (in dollars per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Short-term borrowings, carrying amount Short-Term Debt 2030 Time Deposit Maturities, Year Five Gross Unrealized Gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain Time deposits Deposits, Fair Value Disclosure Measurement Input Type [Domain] Measurement Input Type [Domain] Partnership investments Deferred Tax Assets, Partnership Investment Deferred Tax Assets, Partnership Investment Equity Investments, Indirect, NAV Equity Investments Indirect, NAV [Member] Equity Investments Indirect, NAV [Member] Agency residential collateralized mortgage obligations Agency residential collateralized mortgage obligations Collateralized Mortgage Obligations [Member] Schedule of Assets and Liabilities Measured at Fair Value on Nonrecurring Basis Fair Value Measurements, Nonrecurring [Table Text Block] Leases, Excluding Ground Leases Leases, Excluding Ground Leases [Member] Leases, Excluding Ground Leases [Member] 660 to 749 FICO Score, 660 to 749 [Member] FICO Score, 660 to 749 [Member] Current period gross write-offs, total Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Operating lease liabilities Deferred Tax Assets, Tax Deferred Expense, Operating Lease Liabilities Deferred Tax Assets, Tax Deferred Expense, Operating Lease Liabilities Computer processing Communications and Information Technology Other Unconsolidated Variable Interest Entities Other Unconsolidated Variable Interest Entities [Member] Other Unconsolidated Variable Interest Entities Vesting Contingent on Service Conditions Vesting Contingent On Service Conditions [Member] Vesting Contingent On Service Conditions [Member] Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Accounts and Financing Receivables [Table] Accounts and Financing Receivables [Table] Trading account assets Total trading account securities Debt Securities, Trading, and Equity Securities, FV-NI Net decrease (increase) in other investments Proceeds from Sale of Other Investments Federal deposit insurance Effective Income Tax Rate Reconciliation, FDIC Insurance, Percent Effective Income Tax Rate Reconciliation, FDIC Insurance, Percent Net decrease (increase) in short-term investments, excluding acquisitions Net (increase) decrease in securities available for sale and in short-term and other investments Net Increase Decrease In Short Term Investments Net increase decrease in short term investments. Other comprehensive income before reclassification, net of income taxes OCI, before Reclassifications, Net of Tax, Attributable to Parent Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Total compensation expense for stock-based compensation plans Share-Based Payment Arrangement, Expense Expenditures for additions to long-lived assets Capital Expenditures Additions To Assets Capital Expenditures Additions To Assets Bank notes and other short-term borrowings Interest Expense, Short-Term Borrowings Excluding Federal Funds and Securities Sold under Agreements to Repurchase Hedging Designation [Domain] Hedging Designation [Domain] Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Operating leases Operating Lease, Lease Income [Abstract] Loans held for sale Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance Total liabilities and equity Liabilities and Equity Net pension and postretirement benefit costs Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Number of Options Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Schedule of Changes in Carrying Amount of Mortgage Servicing Assets Servicing Asset at Amortized Cost [Table Text Block] Senior notes Senior Notes, Noncurrent Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Amounts reclassified from accumulated other comprehensive income, net of income taxes Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Escrow earn rate Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Escrow Earn Rate Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Escrow Earn Rate Other Deferred Tax Assets, Other Net prepaid pension cost recognized Liability, Defined Benefit Plan Credit Derivative [Table] Credit Derivative [Table] General Business Tax Credit Carryforward General Business Tax Credit Carryforward [Member] Accounting Policies [Abstract] Accounting Policies [Abstract] Schedule of Lessee, Operating Lease, Maturities of Lease Liabilities Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Senior Notes Due 2027-2035 Senior Notes Due 2027-2035 [Member] Senior Notes Due 2027-2035 Income (loss) from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Treasury Stock, at Cost Treasury Stock, Common [Member] Fair value of units/shares vested Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Year one Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year Tier 1 risk-based capital, leverage capitalized Banking Regulation, Tier 1 Leverage Capital Ratio, Well Capitalized, Minimum Operating lease liabilities Total operating lease liabilities Operating Lease, Liability Equity — International Defined Benefit Plan, Mutual Funds, Equity, Non-US [Member] Defined Benefit Plan, Mutual Funds, Equity, Non-US [Member] Total lease payments Lessor, Operating Lease, Payment to be Received Fair Value Of Assets And Liabilities Measured On Recurring And Non Recurring Basis [Table] Fair Value Of Assets And Liabilities Measured On Recurring And Non Recurring Basis [Table] Fair Value Of Assets And Liabilities Measured On Recurring And Non Recurring Basis [Table] 90 and Greater Days Past Due Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Personnel and other expense Personnel and Other Expense Personnel and Other Expense Preferred stock, liquidation preference (in dollars per share) Preferred Stock, Liquidation Preference Per Share LIABILITIES Liabilities [Abstract] Finance lease cost Finance Lease, Right-of-Use Asset, Amortization Soliciting Material Soliciting Material Minimum period of service at the time of termination hired before 2001 Minimum Period Of Service At Time Of Termination Hired Before Two Thousand One Minimum period of service at the time of termination hired before 2001. Commercial and other Commercial And Other [Member] Commercial And Other [Member] Servicing Assets Servicing Assets [Policy Text Block] Servicing Assets [Policy Text Block] PCCR intangibles Purchased Credit Card Relationship Intangible [Member] Purchased Credit Card Relationship Intangible [Member] Net prepaid pension cost recognized consists of: Liability, Defined Benefit Plan [Abstract] Goodwill impairment charges Goodwill, Impairment Loss Recognized on hedged items Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Regulatory Matters Regulatory Capital Requirements under Banking Regulations [Text Block] Percentage increase or decrease in assumed discount rate Percentage Increase Or Decrease In Assumed Discount Rate Percentage Increase Or Decrease In Assumed Discount Rate Variable Interest Entity [Table] Variable Interest Entity [Table] Accrued income and other assets Increase (Decrease) In Accrued Income And Other Assets Increase (Decrease) In Accrued Income And Other Assets Year three Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer 2028 Lessee, Operating Lease, Liability, to be Paid, Year Three Current period gross write-offs, prior Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff Mandatory deferred incentive awards, vesting rate Mandatory Deferred Incentive Awards Vest At Rate Mandatory Deferred Incentive Awards Vest At Rate Total commercial real estate loans Commercial real estate loans Commercial Real Estate Loans [Member] Total commercial real estate loans. 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excess of collateral posted Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Collateral Posted Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Collateral Posted Income Taxes Income Tax, Policy [Policy Text Block] Other tax benefits Other Tax Expense (Benefit) Net derivative liabilities with credit-risk contingent features Credit Risk Derivative Liabilities, at Fair Value Financing Receivable, Allowance for Credit Loss [Roll Forward] Financing Receivable, Allowance for Credit Loss [Roll Forward] Purchased Loans Acquired Loans Policy [Policy Text Block] Acquired Loans Policy [Text Block] OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Written Communications Written Communications Unguaranteed residual value Sales-Type And Direct Financing Leases, Unguaranteed Residual Asset Sales-Type And Direct Financing Leases, Unguaranteed Residual Asset Net derivatives in the balance sheet Derivative Financial Instruments Assets Liabilities Net [Member] Derivative Financial Instruments Assets Liabilities Net [Member] HELD-TO-MATURITY SECURITIES Held-to-maturity securities: Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss [Abstract] ASSETS MEASURED ON A RECURRING BASIS Assets, Fair Value Disclosure [Abstract] Net proceeds (payments) from issuance of long-term debt Proceeds from (Repayments of) Long-Term Debt and Capital Securities 2027 Time Deposit Maturities, Year Two Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] 2029 Finite-Lived Intangible Asset, Expected Amortization, Year Four Total risk-based capital, regulatory minimum, ratio Banking Regulation, Total Risk-Based Capital Ratio, Capital Adequacy, Minimum Credit Score, FICO [Axis] Credit Score, FICO [Axis] Held-to-maturity securities fair value Fair Value Total Debt Securities, Held-to-Maturity, Fair Value VIE 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Assets, Impact of 10 Percent Adverse Change in Discount Rate Effect on fair value from 20% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Escrow Earn Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Escrow Earn Rate Tax credit investment commitments Tax Credit Investment Commitments Tax Credit Investment Commitments Net change in: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Common equity Tier 1 risk-based capital, actual amount Banking Regulation, Common Equity Tier 1 Risk-Based Capital, Actual Change in valuation allowances Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Historical share price volatility Share-Based Compensation Arrangement by Share-Based 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Recovery of penalties related to unrecognized tax benefits in income tax expense Unrecognized Tax Benefits Including Income Tax Penalties And Interest Accrued Unrecognized Tax Benefits Including Income Tax Penalties And Interest Accrued Interest income – loans Interest Income [Member] Mortgage loans in process of foreclosure Mortgage Loans in Process of Foreclosure, Amount Thereafter Lessor, Operating Lease, Payment to be Received, after Year Five Short-term Debt [Line Items] Short-Term Debt [Line Items] Government-guaranteed and Private Education Lending Business Government-guaranteed And Private Education Lending Business [Member] Government-guaranteed And Private Education Lending Business Net deferred tax assets (liabilities) Deferred Tax Assets, Net Due after ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Lapsed or canceled (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period Carrying amount of hedged item Hedged Liability, Fair Value Hedge Per Common Share — assuming dilution: Earnings Per Share, Diluted [Abstract] 60-89 Days Past Due Financial Asset, 60 to 89 Days Past Due [Member] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Hedging Designation [Axis] Hedging Designation [Axis] Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block] Interest on other borrowed funds Interest Expense, Other Short-Term Borrowings Scenario [Axis] Scenario [Axis] Schedule of Change in Liability for Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Investment banking and debt placement fees Underwriting Discounts Fees And Commissions [Member] Underwriting Discounts Fees And Commissions [Member] Total expense Interest And Non Interest Expenses Interest And Non Interest Expenses PBO Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation California CALIFORNIA Federal deposit insurance Effective Income Tax Rate Reconciliation, FDIC Insurance, Amount Effective Income Tax Rate Reconciliation, FDIC Insurance, Amount Realized gains (losses) (pre-tax) reclassified from AOCI into net income Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Derivative Contract [Domain] Derivative Contract [Domain] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Net proceeds from reissuance of Common Shares Proceeds from Issuance of Common Stock 2030 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Realized (losses) Debt Securities, Available-for-Sale, Realized Loss Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Options expiration years Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Number of retail branches Number Of Retail Branches Number Of Retail Branches Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Schedule of Activity and Pricing Information for Nonvested Shares in Long-Term Incentive Compensation Program Activity and Pricing Information For Nonvested Shares in Long Term Incentive Compensation Program Text Block [Table Text Block] Activity and pricing information for nonvested shares in long term incentive compensation program. 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Net pension and postretirement benefit costs, net of income taxes of $(20), $8, and $0 Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Open market common share repurchases Payments For Repurchase Of Common Stock, Open Market Payments For Repurchase Of Common Stock, Open Market Federal tax credits Deferred Tax Assets, Tax Credit Carryforwards Commercial credit card Credit cards Credit Card Receivable [Member] Leases Lessor, Operating Leases [Text Block] Reclassification of net losses related to terminated cash flow hedges from AOCI to income Terminated Cash Flow Hedge Gain Loss Reclassified To Earnings Net Estimate The amount of net gains or losses on a terminated cash flow hedge expected to be reclassified in the next reporting period to earnings from accumulated other comprehensive income. Forecast Forecast [Member] Net capital loss carryforwards Deferred Tax Assets, Capital Loss Carryforwards Short-term investments Interest Income, Operating Title of 12(b) Security Title of 12(b) Security Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] State net operating losses and credits Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Age of employees under condition one Age Of Employees Under Condition One Age of employees under condition one. Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Percentage of estimated fair value in excess of carrying amount Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount Equipment Equipment Expense Income (loss) from continuing operations attributable to Key common shareholders (in dollars per share) Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in dollars per share) Income Loss From Continuing Operations Attributable To Key Commons Shareholders Per Diluted Share The amount of income (loss) from continuing operations after adjustments for income (loss) attributable to non-controlling interest and dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period) available to each share of common stock outstanding during the reporting period and each share that would have been outstanding assuming the issuance of common shares for all dilutive potential common shares outstanding during the reporting period. Earnings Per Share [Abstract] Earnings Per Share [Abstract] 2030 Lessee, Operating Lease, Liability, to be Paid, Year Five Credit carryforward Tax Credit Carryforward, Amount Current period gross write-offs, Year three Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff Net income (expense) recognized on fair value hedges Gain (Loss) on Fair Value Hedges Recognized in Earnings Purchases are limited to any calendar year Maximum Limit Of Purchase Of Shares In Any Calendar Year Maximum Limit Of Purchase Of Shares In Any Calendar Year Period of service under condition two Period Of Service Under Condition Two Period of service under condition two. Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Open market Common Share repurchases (in shares) Treasury Stock, Shares, Acquired Exercised (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Amount of offset in excess of cash collateral held Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Collateral Held Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Collateral Held LIHTC investments Variable Interest Sponsors [Member] Variable Interest Sponsors [Member] Servicing Asset at Amortized Cost [Line Items] Servicing Asset at Amortized Cost [Line Items] Measurement Frequency [Domain] Measurement Frequency [Domain] Federal Home Loan Bank advances Federal Home Loan Bank Advances [Member] ASSETS MEASURED ON A NONRECURRING BASIS Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract] Fair value, investments, entities that calculate net asset value per share, unfunded commitments Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments Amortization Servicing Asset at Amortized Cost, Amortization Shareholders' Equity Equity [Text Block] State Deferred State and Local Income Tax Expense (Benefit) Loan Restructuring Modification [Domain] Loan Restructuring Modification [Domain] Net loans Total loans Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss Illinois ILLINOIS NET INCOME (LOSS) Net income (loss) Net income (loss) attributable to Key Net Income (Loss) Attributable to Parent Recourse agreement with FNMA Recourse agreement with FNMA Underwriting And Servicing Program [Member] Underwriting and servicing program. Equity Method Investment, Nonconsolidated Investee [Domain] Equity Method Investment, Nonconsolidated Investee [Domain] Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $(137), $(104), and $(114) Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), after Adjustments and Tax, Parent Total risk-based capital, actual ratio Banking Regulation, Total Risk-Based Capital Ratio, Actual Construction in process Construction in Progress [Member] Operating lease income related to lease payments Operating Lease, Lease Income, Lease Payments Schedule of Total Income Tax Expense (Benefit) and Resulting Effective Tax Rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Short-term investments held for discharge of obligations Short Term Investments Held For Discharge Of Obligations Short Term Investments Held For Discharge Of Obligations Vesting period for compensation cost Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Weighted-average cost of common shares issued under the plan (in dollars per share) Weighted Average Cost Of Shares Issued Under Plan Weighted Average Cost Of Shares Issued Under Plan Insignificant level 3 assets, net of liabilities Insignificant Assets (Liabilities), Net, Fair Value Disclosure Insignificant Assets (Liabilities), Net, Fair Value Disclosure Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Repurchase of Treasury Shares Payments for Repurchase of Common Stock Contract assets Contract with Customer, Asset, after Allowance for Credit Loss Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Sale or repayments of advances to subsidiaries Proceeds from Collection of Long-Term Loans to Related Parties Line of Credit Line of Credit [Member] Stock-Based Compensation Compensation Related Costs, Policy [Policy Text Block] Retained earnings Retained Earnings (Accumulated Deficit) Number of days to designate the charge-off policy for most consumer loans taking effect, payment due period Allowance For Consumer Loans Payment Due Period Allowance for consumer loans payment due period. Residual cash flows discount rate Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate Purchases of held-to-maturity securities Payments to Acquire Held-to-Maturity Securities Increase in cash surrender value of corporate-owned life insurance Life Insurance, Corporate or Bank Owned, Change in Value Class of Stock [Axis] Class of Stock [Axis] Unrealized gains (losses) on derivative financial instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Employees contribution to saving plan Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Common equity Tier 1 risk-based capital, regulatory minimum with stress capital buffer Banking Regulation, Capital Conservation Buffer, Common Equity Tier 1 Risk-Based Capital, Actual Other Deferred Tax Liabilities, Other Retirement Plan Type [Axis] Retirement Plan Type [Axis] Credit Derivatives [Line Items] Credit Derivatives [Line Items] Statement [Table] Statement [Table] Actual return on plan assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Total deferred Deferred Income Tax Expense (Benefit) Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] FINANCING ACTIVITIES Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Less than 660 FICO Score, Less than 660 [Member] FICO Score, Less than 660 [Member] Contract liabilities Contract with Customer, Liability Allocated income taxes (benefit) and TE adjustments Income Tax Expense (Benefit) and Taxable Equivalent Adjustments Income Tax Expense (Benefit) and Taxable Equivalent Adjustments Trading account assets Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI Interest Rate Reduction Contractual Interest Rate Reduction [Member] Amendment Flag Amendment Flag Fixed price per share (in dollars per share) Sale of Stock, Price Per Share Total income tax benefit recognized for stock-based compensation plans Share-Based Payment Arrangement, Expense, Tax Benefit Authorized number of shares that may be issued as equity awards (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized Available-for-sale securities, accrued interest Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss Postretirement Benefit Plan Other Postretirement Benefits Plan [Member] Rolling period in which a certain percentage of common stock cannot be granted as options Share-based Compensation Arrangement by Share-based Payment Award, Period Applicable to Outstanding Stock Maximum Share-based Compensation Arrangement by Share-based Payment Award, Period Applicable to Outstanding Stock Maximum Schedule of Allocation of Plan Assets Schedule of Allocation of Plan Assets [Table Text Block] Transfers and Servicing [Abstract] Treasury stock, at cost (154,301,387 and 149,915,630 shares) Treasury Stock, Common, Value 2026 Sales-Type and Direct Financing Leases, Payment to be Received, Year One 2028 Time Deposit Maturities, Year Three Allowance for loan and lease losses Beginning balance Ending balance Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Net investment in sales-type and direct financing leases Net Investment In Sales-Type And Direct Financing Leases Net Investment In Sales-Type And Direct Financing Leases Amortization period of stock-based compensation awards Stock Awards Amortization Period Stock Awards Amortization Period Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Income (loss) from continuing operations attributable to Key common shareholders Income (loss) from continuing operations attributable to Key common shareholders Income Loss From Continuing Operations Attributable To Key Common Shareholders Income (loss) from continuing operations after adjustments for noncontrolling interest and dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period). Nonbank subsidiaries Nonbank Subsidiaries [Member] Nonbank Subsidiaries [Member] Weighted-average Common Shares outstanding (in shares) Weighted-average Common Shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic New Jersey NEW JERSEY Unrecognized tax benefits Balance at beginning of year Balance at end of year Unrecognized Tax Benefits that Would Impact Effective Tax Rate Secured borrowing Secured Borrowing [Member] Secured Borrowing Due Through 2025 [Member] Schedule of Basic and Diluted Earnings Per Common Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Exercisable, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number Segment Reporting [Abstract] Segment Reporting [Abstract] Ownership interest per depositary share ratio Entity Listing, Depository Receipt Ratio Operating lease expense Operating Lease, Expense Number of performance units vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested, Number of Shares Debt Disclosure [Abstract] Debt Disclosure [Abstract] Temporarily impaired securities, fair value, less than 12 months Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value Available for sale and held to maturity securities continuous unrealized loss position less than twelve months fair value. Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Scenario [Domain] Scenario [Domain] Remaining weighted-average life of standby letters of credit in years Remaining Weighted Average Life Of Standby Letters Of Credit Remaining weighted-average life of standby letters of credit. Restricted Stock Unit Restricted Stock Unit [Member] Restricted Stock Unit [Member] Expected defaults Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses Appraised value Valuation, Appraised Value [Member] Valuation, Appraised Value [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Consolidated Entities [Axis] Consolidated Entities [Axis] Common shares, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Employee benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits 2030-2034 Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Loans included in divestiture Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Use of Estimates Use of Estimates, Policy [Policy Text Block] Leases Lessor, Direct Financing Leases [Text Block] Total risk-based capital, actual amount Banking Regulation, Total Capital, Actual Current liabilities Liability, Defined Benefit Plan, Current Cash dividends paid Payments of Dividends Net occupancy Occupancy, Net Lease receivables Sales-type and Direct Financing Leases, Lease Receivable Prior Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year Current Financial Asset, Not Past Due [Member] Schedule of Derivative Instrument Cash Flow Hedge Earning Recognized by Income Statement Location Schedule Of Cash Flow Hedging Instruments Statements Of Financial Performance [Table Text Block] Schedule of cash flow hedging instruments statements of financial performance. Total liabilities VIE, liabilities Total Liabilities Liabilities Temporarily impaired securities, gross unrealized losses, 12 months or longer Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Aggregate Losses Available for sale and held to maturity securities continuous unrealized loss position twelve months or longer aggregate losses. Percentage of Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Modified in Period, to Total Financing Receivables, Percentage Series G Preferred Stock Series G Preferred Stock [Member] Financial Instrument Performance Status [Domain] Financial Instrument Performance Status [Domain] Income (loss) from discontinued operations Income (loss) from discontinued operations, net of taxes Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax Asset-backed securities Asset-Backed Securities [Member] Consolidation Items [Axis] Consolidation Items [Axis] Estimated change in net pension cost due to discount rate Estimated Change In Net Pension Cost Due To Discount Rate Estimated Change In Net Pension Cost Due To Discount Rate Proceeds from prepayments and maturities of held-to-maturity securities Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities Held-to-maturity securities (fair value: $8,313 and $6,837) Held-to-maturity securities Amortized Cost Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss Vesting Contingent on Performance and Service Conditions - Payable in Stock Vesting Contingent On Performance And Service Conditions, Payable In Stock [Member] Vesting Contingent On Performance And Service Conditions, Payable In Stock [Member] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Collateral posted Collateral Already Posted, Aggregate Fair Value