Deposits with no stated maturity Deposits With No Stated Maturity Deposits with no stated maturity. Schedule of Components of Short-Term Borrowings Schedule of Short-Term Debt [Table Text Block] Net unrealized gains (losses) on derivative financial instruments, tax Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), Adjustments, Tax Commodity Commodity Contract [Member] Probability of default Measurement Input, Default Rate [Member] Held-to-Maturity Securities, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date [Abstract] Netting adjustments Derivative assets, netting adjustments Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash, Offset Against Derivative Asset Award Timing Predetermined Award Timing Predetermined [Flag] Servicing retained from loan sales Servicing Asset at Amortized Cost, Other Changes that Affect Balance, Amount Credit and liquidity discount Measurement Input, Credit And Liquidity Discount [Member] Measurement Input, Credit And Liquidity Discount Entity File Number Entity File Number Credit Credit Risk Contract [Member] Capital Surplus Additional Paid-in Capital [Member] Tabular List, Table Tabular List [Table Text Block] Discount rate assumption Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Discount Rate Moderate Risk Level, Medium [Member] Charge-offs Financing Receivable, Allowance for Credit Loss, Writeoff Combination Combination Loan Modification [Member] Combination Loan Modification Schedule of Fair Value Disclosures of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Maximum Potential Undiscounted Future Payments Guarantor Obligations, Maximum Exposure, Undiscounted Noninterest-bearing deposits Noninterest-Bearing Deposit Liabilities, Domestic Position [Axis] Position [Axis] Measurement Basis [Axis] Measurement Basis [Axis] Adjustment to Compensation: Adjustment to Compensation [Axis] Fair value, 12 months or longer Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Revenue from Contracts with Customers Revenue from Contract with Customer [Text Block] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] Schedule of Stock by Class [Table] Stock, Class of Stock [Table] Other collateral Counterparty And Cash Collateral Netting [Member] Counterparty and Cash Collateral Netting [Member] Total charge-offs, including discontinued operations Financing Receivable, Allowance for Credit Loss, Writeoff, Including Discontinued Operations Financing Receivable, Allowance for Credit Loss, Writeoff, Including Discontinued Operations Loans, net of unearned income (residential), measurement input Loans Held-For-Investment, Measurement Input Loans Held-For-Investment, Measurement Input Netting adjustments Derivative liabilities, netting adjustments Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Offset Residential mortgage reserve Residential Mortgage Reserve [Member] Residential Mortgage Reserve [Member] Continuing Operations Continuing Operations [Member] Discontinued assets Disposal Group, Including Discontinued Operation, Assets Adjustment to Compensation, Amount Adjustment to Compensation Amount Consolidation Consolidation, Policy [Policy Text Block] Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense Notional Amount Derivative Asset, Notional Amount Employee Stock Option Share-Based Payment Arrangement, Option [Member] Loans, net of allowance Financing Receivable, after Allowance for Credit Loss Other Other Loan Modification [Member] Other Loan Modification Cash dividends declared on common shares Dividends, Common Stock, Cash Total equity Beginning balance Ending balance Equity, Attributable to Parent Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-Sale [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Insider Trading Policies and Procedures [Line Items] Effect on Fair Value of a 20% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Discount Rate Common shares, shares authorized (in shares) Common Stock, Shares Authorized Interest Income - securities Interest Income, Securities [Member] Interest Income, Securities Recurring Fair Value, Recurring [Member] Originations of loans held for sale, net of repayments Originations Of Loans Held For Sale Net Of Repayments Originations of loans held for sale net of repayments. Cover [Abstract] Cover [Abstract] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Discontinued Operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Maximum Maximum [Member] Loans transferred to OREO Real Estate Owned, Transfer to Real Estate Owned Temporarily impaired securities, fair value, 12 months or longer Available for Sale Securities and Held to Maturity Securities Continuous Unrealized Loss Position Twelve Months or Longer Fair Value Available for sale securities and held to maturity securities continuous unrealized loss position twelve months or longer fair value. Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position Due after ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Comparability factor Measurement Input, Comparability Adjustment [Member] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Weighted-average Term Extension (in years) Financing Receivable, Modified, Weighted Average Term Increase from Modification INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Revolving Loans Converted to Term Loans Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Total interest expense Interest Expense, Operating 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 Derivative assets before collateral Derivative Assets Before Cash Collateral Derivative assets before cash collateral. Document Fiscal Period Focus Document Fiscal Period Focus Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Schedule of Quantitative Information about Level 3 Fair Value Measurements Fair Value Option, Disclosures [Table Text Block] Award Timing Method Award Timing Method [Text Block] Total Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, after Allowance for Credit Loss Award Type Award Type [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Parent Company Parent Company [Member] Total recoveries, including discontinued operations Financing Receivable, Allowance for Credit Loss, Recovery, Including Discontinued Operations Financing Receivable, Allowance for Credit Loss, Recovery, Including Discontinued Operations Trading Symbol Trading Symbol Long-term debt Interest expense — Long-term debt Interest Expense, Long-Term Debt Common Shares reissued (returned) for stock options and other employee benefit plans (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Accrued expense and other liabilities Accrued Liabilities and Other Liabilities Entity Address, City or Town Entity Address, City or Town Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Net reduction to interest income Net Reduction To Interest Income Net reduction to interest income. Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Increase (decrease) in ALLL (as a percent) Financing Receivable, Allowance For Credit Loss, Percentage Financing Receivable, Allowance For Credit Loss, Percentage Entity Emerging Growth Company Entity Emerging Growth Company Gross unrealized losses, less than 12 months Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Total noninterest income Noninterest income Total noninterest income Noninterest Income Beginning balance, Common Shares (in shares) Ending balance, Common Shares (in shares) Common Stock, Shares, Outstanding Net losses (gains) on sales of loans held for sale Gain (Loss) on Sales of Loans, Net Schedule of Range and Weighted-Average of Significant Unobservable Inputs Schedule Of Estimation Of Fair Value Of Servicing Rights Using Key Economic Assumptions [Table Text Block] Schedule of estimation of fair value of servicing rights using key economic assumptions. 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 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 Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] 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. Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Liability Recorded Guarantor Obligations, Current Carrying Value Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] 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 Commercial Bank Corporate Banking [Member] Corporate banking. 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 Commercial and Industrial [Member] Commercial and Industrial Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Income taxes Income Tax Expense (Benefit) Income (loss) from discontinued operations, net of taxes (in usd 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] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Hedge accounting basis adjustment - active hedges Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Hedging Relationship [Axis] Hedging Relationship [Axis] Cash and other 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 Unpaid principal balance outstanding of loans sold Recorded Unconditional Purchase Obligation Discontinued Operations and Disposal Groups [Abstract] Indirect investments Principal Indirect Investments [Member] Principal indirect investments. Schedule of Guarantor Obligations [Table] Guarantor Obligation [Table] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Class of Treasury Stock [Table] Class of Treasury Stock [Table] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Mortgage Servicing Assets Mortgage Servicing Assets [Text Block] Mortgage servicing assets. NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Escrow earn rate assumption 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 Debt securities, held-to-maturity, purchase of senior notes Debt Securities, Held-To-Maturity, Purchase of Senior Notes Debt Securities, Held-To-Maturity, Purchase of Senior Notes Proceeds from sales of securities available for sale Proceeds from Sale of Debt Securities, Available-for-Sale Securities available for sale Total securities available for sale Fair Value Total Debt Securities, Available-for-Sale, Excluding Accrued Interest Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Recoveries Financing Receivable, Allowance for Credit Loss, Recovery NET INTEREST INCOME Interest Income (Expense), Operating Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Loans transferred to portfolio from held for sale Loan, Transfer from Held-for-Sale to Held-in-Portfolio Derivative liabilities Derivative Liabilities Derivative Liability, Subject to Master Netting Arrangement, before Offset Equity Components [Axis] Equity Components [Axis] Three years prior Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Consumer mortgage income Consumer Mortgage Income [Member] Consumer Mortgage Income [Member] Servicing Asset [Abstract] Servicing Asset [Abstract] Total commercial real estate loans Commercial Real Estate [Member] Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Entity Address, State or Province Entity Address, State or Province Total interest income Interest and Dividend Income, Operating Financial Asset, Period Past Due [Domain] Financial Asset, Aging [Domain] Financial Asset, Aging [Domain] 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. Individual: Individual [Axis] Entities [Table] Entities [Table] Amortization of investment Amortization Number of loan modifications Financing Receivable, Modifications, Number of Loans Financing Receivable, Modifications, Number of Loans Balance at beginning of period Balance at end of period Servicing Asset at Amortized Cost Maximum Exposure to Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Payments on long-term debt Repayments of Long-Term Debt Leases Lessor, Sales-type Leases [Text Block] Entity Interactive Data Current Entity Interactive Data Current Interest expense – long-term debt Interest Expense, Long-Term Debt [Member] Interest Expense, Long-Term Debt [Member] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Securities available for sale Interest Income - securities Interest Income, Debt Securities, Available-for-Sale, Operating Financing Receivable, Troubled Debt Restructuring [Line Items] Financing Receivable, Modified [Line Items] INTEREST INCOME Interest and Dividend Income, Operating [Abstract] Total noninterest expense Noninterest Expense Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Deposits Interest Expense, Deposits NONINTEREST INCOME Noninterest Income [Abstract] Series D Preferred Stock Series D Preferred Stock [Member] Other consumer loans Other consumer loans Other Consumer Loans [Member] Other Consumer Loans Entity Central Index Key Entity Central Index Key PEO Name PEO Name Senior Notes Due 2027-2037 Senior Notes Due 2027-2037 [Member] Senior Notes Due 2027-2037 Schedule of Changes in Liability for Credit Losses on Off-Balance Sheet Exposures Financing Receivables, Off-Balance Sheet, Liabilities [Table Text Block] Financing Receivables, Off-Balance Sheet, Liabilities [Table Text Block] Total revenue (TE) Revenues Total net gains (losses) Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Schedule of Financing Receivable Credit Quality Indicators Financing Receivable Credit Quality Indicators [Table Text Block] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Book value (net of capital surplus) Preferred Stock, Including Additional Paid in Capital, Net of Discount Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Fair value at end of period Servicing Asset at Amortized Cost, Fair Value Other mortgage-backed securities Mortgage-Backed Securities, Other [Member] Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Class of Stock [Domain] Class of Stock [Domain] Hedge accounting basis adjustment Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) Fair Value Option, Disclosures [Table] Fair Value Option, Disclosures [Table] Balance Sheet Location [Axis] Statement of Financial Position Location, Balance [Axis] Maximum length of time over which forecasted transactions are hedged (in years) Maximum Length Of Time Over Which Forecasted Transactions Are Hedged Maximum length of time over which forecasted transactions are hedged. Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] 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 Accumulated Other Comprehensive Income (Loss) 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] Revolving Loans Converted to Term Loans Amortized Cost Basis, writeoff 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 Assessment [Domain] Internal Credit Assessment [Domain] Derivatives and Hedging Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Real Estate Residential Mortgage and Home Equity Loans Real Estate Residential Mortgage And Home Equity Loans [Member] Real Estate Residential Mortgage And Home Equity Loans Fair Value as of Grant Date Award Grant Date Fair Value Allocated bad debt deductions Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Bad Debt Reserve for Tax Purposes of Qualified Lender Four years prior Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year Schedule of Components of Long-Term Debt Schedule of Long-Term Debt Instruments [Table Text Block] Personnel Personnel expense Labor and Related Expense Cards and payments income Cards And Payments [Member] Cards And Payments [Member] Unpaid principal balance of loans sold during the period Continuing Involvement with Transferred Financial Assets, Principal Amount Outstanding Servicing Asset at Amortized Cost [Table] Servicing Asset at Amortized Cost [Table] Effect of Common Share options and other stock awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Document Quarterly Report Document Quarterly Report Fair value, less than 12 months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Corporate-owned life insurance income Bank Owned Life Insurance Income Long-term debt, fair value Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Financial Instrument Performance Status [Axis] Financial Instrument Performance Status [Axis] Gross unrealized losses, 12 months or longer Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Other income Other Income [Member] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Loans Insured or Guaranteed by Government Authorities [Domain] Loans Insured or Guaranteed by Government Authorities [Domain] Investment Type [Axis] Investment Type [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Net interest income (TE) Interest Income (Expense), Net, Taxable Equivalent Interest Income (Expense), Net, Taxable Equivalent Non-PEO NEO Non-PEO NEO [Member] Amortization of losses Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gain (Loss) Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Net Actuarial Gain (Loss) Attributable to Parent Position [Domain] Position [Domain] Other Corporate And Reconciling Items [Member] Corporate And Reconciling Items [Member] Preferred stock, dividend rate (as a percent) Preferred Stock, Dividend Rate, Percentage Other investments Interest Income, Other Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Sale of Stock [Axis] Sale of Stock [Axis] Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Reduction of secured borrowing and related collateral Reduction Of Secured Borrowing And Related Collateral Reduction of secured borrowing and related collateral. All Award Types Award Type [Domain] Net Gains (Losses) Recognized in OCI Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax Education Lending Education Lending [Member] Education lending. Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Trial Modification Plans Trial Modification Plans [Member] Trial Modification Plans Federal funds purchased and securities sold under repurchase agreements Interest Expense, Federal Funds Purchased and Securities Sold under Agreements to Repurchase Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Foreign exchange Foreign Exchange Contract [Member] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Estimate of Fair Value Measurement Estimate of Fair Value Measurement [Member] Accrued Income And Other Assets Accrued Income And Other Assets [Member] Accrued Income And Other Assets [Member] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Derivative Assets, net Derivative Asset, Subject to Master Netting Arrangement, before Offset of Collateral Due after one through five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Fair Value, Option, Quantitative Disclosures [Line Items] Fair Value, Option, Quantitative Disclosures [Line Items] Financing receivable, unearned income Financing Receivable, Deferred Commitment Fee Due after five through ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Financing Receivable, Past Due [Line Items] Financing Receivable, Past Due [Line Items] Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Credit cards Consumer Credit Card [Member] Consumer credit card. Financial Instruments [Domain] Financial Instruments [Domain] Due after ten years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Guarantee obligations (as a percent) Guarantor Obligations, Liquidation Proceeds, Percentage Commercial loans Commercial Loans Fair Value Disclosure Commercial loans fair value disclosure. Low Risk Level, Low [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Net Gains (Losses) Reclassified From AOCI Into Income Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Pledging Purpose [Domain] Pledging Purpose [Domain] Effect on Fair Value of a 10% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Prepayment Speed Minimum Minimum [Member] Net interest income after provision for credit losses Interest Income (Expense), after Provision for Loan Loss Accrued interest Financing Receivable, Accrued Interest, before Allowance for Credit Loss Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Company Selected Measure Name Company Selected Measure Name Fair Value Measurement [Domain] Fair Value Measurement [Domain] Loss given default Measurement Input, Loss Given Default [Member] Measurement Input, Loss Given Default [Member] Borrowings Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Discontinued operations Discontinued Operations [Member] Due after ten years Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 10 Net gain (loss) on cash flow hedging relationships Cash Flow Hedges Derivative Instruments at Fair Value, Net [Abstract] Total ALLL, including discontinued operations, beginning balance Total ALLL, including discontinued operations, ending balance Financing Receivable, Allowance For Credit Loss, Including Discontinued Operations Financing Receivable, Allowance For Credit Loss, Including Discontinued Operations Weighted-average Common Shares and potential Common Shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Commercial Bank Commercial Bank [Member] Commercial Bank [Member] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Home equity loans Home Equity Loan [Member] Proceeds from corporate-owned life insurance Proceeds from Life Insurance Policy Deposits in domestic offices: Deposits, Domestic [Abstract] Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Net decrease (increase) in loans, excluding acquisitions, sales and transfers Net Decrease Increase In Loans Excluding Acquisitions Sales And Transfers The net change in the total loans, excluding acquisitions, sales and transfers. Beginning balance, Preferred Shares (in shares) Ending balance, Preferred Shares (in shares) Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Document Transition Report Document Transition Report Due after one through five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Long-term debt Long-Term Debt [Member] Preferred stock, amount outstanding Preferred Stock, Value, Outstanding Underlying Securities Award Underlying Securities Amount Gross realized gains Debt Securities, Available-for-Sale, Realized Gain Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date Subsequent Events Subsequent Events, Policy [Policy Text Block] Income Taxes Income Tax Disclosure [Text Block] Net asset value Fair Value, Investments, Entities That Calculate Net Asset Value Per Share, Fair Value Fair Value, Investments, Entities That Calculate Net Asset Value Per Share, Fair Value Hedged asset, fair value hedge, portfolio layer method, hedged layer, fair value, cumulative increase (decrease) Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Fair Value, Cumulative Increase (Decrease) Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Provision for credit losses Financing Receivable Allowance For Credit Losses lending related commitments Financing receivable allowance for credit losses lending related commitments. Hedged layer amount Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Amount Document Type Document Type Level 3 Fair Value, Inputs, Level 3 [Member] Earnings Per Common Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Marketing Marketing and Advertising Expense Capital surplus Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Federal Home Loan Bank advances Long-Term Federal Home Loan Bank Advances Writeoff, Revolving Loans Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Revolving, Writeoff Total revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Proceeds from sales of loans held for sale Proceeds from Sale, Loan, Held-for-Sale Statistical Measurement [Axis] Statistical Measurement [Axis] Trust and investment services income Trust And Investment Services Income Trust And Investment Services Income Amount authorized to be repurchased Share Repurchase Program, Authorized, Amount Credit Score, FICO [Domain] Credit Score, FICO [Domain] Writeoff, one year period Writeoff, one year Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff Loans Interest income – loans Interest income — Loans Interest and Fee Income, Loan and Lease, Held-in-Portfolio Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Disposal Group Name [Axis] Disposal Group Name [Axis] Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Investment banking and debt placement fees Investment Banking And Debt Placement [Member] Investment Banking And Debt Placement [Member] Net income (loss) attributable to Key common shareholders Net income (loss) attributable to Key common shareholders Net Income (Loss) Available to Common Stockholders, Basic Commercial mortgage servicing fees Fees and Commissions, Mortgage Banking and Servicing Standby letters of credit Financial Standby Letter of Credit [Member] Entity Information [Line Items] Entity Information [Line Items] Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Total loans modified in last 12 months Financing Receivable, Excluding Accrued Interest, Modified, after 12 Months Level 1 Fair Value, Inputs, Level 1 [Member] Commercial lease financing Commercial Lease Financing [Member] Commercial lease financing. Consumer mortgage income Consumer Mortgage Income Consumer Mortgage Income Accrued expense and other liabilities Increase (Decrease) in Accrued Liabilities Net income (loss) attributable to Key common shareholders (in usd per share) Earnings Per Share, Diluted Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Noncash items: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Due after five through ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Loan restructuring trial modifications amount Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount Cash dividends declared on preferred stock Dividends, Preferred Stock, Cash Junior Subordinated Debentures Due 2028-2037 Junior Subordinated Debentures Due 2028-2037 [Member] Junior Subordinated Debentures Due 2028-2037 Treasury stock, shares (in shares) Treasury Stock, Common, Shares SUMMARY OF OPERATIONS Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract] Consolidation Items [Domain] Consolidation Items [Domain] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Collateral netted against derivative liabilities Cash Collateral Netted Against Derivative Liabilities Cash collateral netted against derivative liabilities. Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Loans and leases Average Loans And Leases Average loans and leases. Term Extension Extended Maturity [Member] Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] No Score FICO Score, No Score [Member] FICO Score, No Score [Member] Schedule of Credit Derivatives Sold and Held Disclosure of Credit Derivatives [Table Text Block] Income taxes paid (refunded) Income Taxes Paid, Net Servicing cost Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Servicing Cost Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Servicing Cost Subsidiaries Subsidiaries [Member] Premises and equipment Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Derivative assets, measurement input Derivative Asset, Measurement Input Loans, net of unearned income of $295 and $303 Total loans Total Loans, net of unearned income (residential) Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss Securities sold under repurchase agreements Securities Sold under Agreements to Repurchase Net income (expense) recognized on cash flow hedges Gain (Loss) on Derivative Instruments, Net, Pretax Schedule of Operating Lease, Lease Income Operating Lease, Lease Income [Table Text Block] Schedule of Securities in an Unrealized Loss Position Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Expiration Date Trading Arrangement Expiration Date Basis adjustments for securities Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Fair Value, Cumulative Increase (Decrease), Excluded from Amortized Cost Prepayment rate assumption Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed Net unrealized gains (losses) on securities available for sale, net of income taxes of $55 and $(136) Other Comprehensive Income (Loss), Available-for-Sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Investments Investments [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Construction Real estate — construction Construction Loans [Member] Entity Current Reporting Status Entity Current Reporting Status Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Consolidated Entities [Domain] Consolidated Entities [Domain] Due in one year or less Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One EARNINGS Earnings [Abstract] Earnings. Financial Instrument [Axis] Financial Instrument [Axis] Sales-type and direct financing leases Sales-Type And Direct Financing Lease, Lease Income [Abstract] Sales-Type And Direct Financing Lease, Lease Income [Abstract] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Executive Category: Executive Category [Axis] Gross unrealized losses, 12 months or longer Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Market comparable pricing Valuation, Market Approach [Member] Net proceeds from issuance of long-term debt Proceeds from Issuance of Long-Term Debt Current Fiscal Year End Date Current Fiscal Year End Date Gross unrealized losses, less than 12 months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Collateral-dependent loans Impaired Loans, Fair Value Disclosure Impaired loans fair value disclosure. Total deposits Deposits Deferred compensation Adjustments To Additional Paid In Capital, Increase (Decrease) From Deferred Compensation Arrangement Adjustments To Additional Paid In Capital, Increase (Decrease) From Deferred Compensation Arrangement Schedule of Significant Macroeconomic Variables of Loan Portfolios Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Schedule of Guarantees Schedule of Guarantor Obligations [Table Text Block] Business services and professional fees Professional Fees Total derivative liabilities Derivative Liability Other expense Other expense Other Noninterest Expense Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Pass Pass [Member] Loan Restructuring Modification [Axis] Loan Restructuring Modification [Axis] Interest rate Interest Rate Contract [Member] Gross Unrealized Losses Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Tax credit of investment Investment Tax Credit Unrecognized tax benefits Unrecognized Tax Benefits WEIGHTED-AVERAGE COMMON SHARES Weighted Average Number of Shares Outstanding, Diluted [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Schedule of Past Due Loans Including Current Loans Financing Receivable, Past Due [Table Text Block] Short positions Bank Notes And Other Short-term Borrowings, Fair Value Bank Notes And Other Short-term Borrowings, Fair Value Leases Lessee, Operating Leases [Text Block] NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Measure: Measure [Axis] Provision Financing Receivable, Credit Loss, Expense (Reversal) Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Employee equity compensation program Common Share repurchases Payments for Repurchase of Other Equity Trust and investment services income Trust And Investment Services [Member] Trust And Investment Services [Member] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Total consumer loans Consumer Portfolio Segment [Member] Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items] Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items] Effect on Fair Value of a 20% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Prepayment Speed Schedule of Reclassifications Out of AOCI Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] 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 Loan Assumption Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Loan Assumption Rate Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Entity Tax Identification Number Entity Tax Identification Number Discounted cash flow Valuation Technique, Discounted Cash Flow [Member] Scotiabank Investment Agreement Scotiabank Investment Agreement [Member] Scotiabank Investment Agreement Schedule of Assumptions and Information for Originated Mortgage Servicing Right Additions Schedule of Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets [Table Text Block] Writeoff, three year period Writeoff, three year Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff Schedule of Variable Interest Entities Information Schedule of Variable Interest Entities [Table Text Block] Criticized (Nonaccruing) Criticized Nonaccruing [Member] Criticized Nonaccruing [Member] Short positions Short [Member] Common shares, shares issued (in shares) Common Stock, Shares, Issued Commercial Mortgage Backed Securities Agency commercial mortgage-backed securities Commercial Mortgage-Backed Securities [Member] Net losses (gains) on leased equipment Gains Losses On Leased Equipment Gains on leased equipment. Loans transferred to held for sale from portfolio Loan and Lease, Transfer from Held-in-Portfolio to Held-for-Sale Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Operating lease income and other leasing gains Total operating lease income and other leasing gains Operating Lease, Lease Income Series E Preferred Stock Series E Preferred Stock [Member] Security Exchange Name Security Exchange Name Total lease income Lease Income 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 Loans held for sale Interest and Fee Income, Loan and Lease, Held-for-Sale Asset Quality Financing Receivables [Text Block] 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. Effect on fair value from 10% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Loan Assumptions Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Loan Assumptions Rate 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 usd 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. Asset Class [Domain] Asset Class [Domain] Total trading account assets Trading Accounts Asset Trading Accounts Asset Equity Investments Direct, NAV Equity Investments Direct, NAV [Member] Equity Investments Direct, NAV [Member] Statement [Line Items] Statement [Line Items] Subordinated Notes Due 2026- 2032 Subordinated Notes Due 2026- 2032 [Member] Subordinated Notes Due 2026- 2032 Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Consumer Bank Consumer Bank [Member] Consumer Bank [Member] Deferred income taxes (benefit) Increase (Decrease) in Deferred Income Taxes Common Shares Common Stock [Member] 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] Statistical Measurement [Domain] Statistical Measurement [Domain] NMTC NMTC [Member] NMTC Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Underlying Asset Class [Axis] Underlying Asset Class [Axis] Collateral-dependent loans, measurement input Impaired Loan, Measurement Input Impaired Loan, Measurement Input Short-term borrowings, fair value 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] Commercial mortgage Real estate — commercial mortgage Commercial Real Estate Commercial Mortgage [Member] Commercial real estate commercial mortgage. Corporate-owned life insurance Bank Owned Life Insurance Leases [Abstract] Leases [Abstract] Junior subordinated debentures Subordinated Long-Term Debt, Noncurrent Fair Value Debt Securities, Held-to-Maturity, Unrealized Loss Position, Fair Value Percentage of carrying amount of our commercial nonperforming loans outstanding (as a percent) Percentage Of Carrying Amount Of Our Commercial Nonperforming Loans Outstanding Percentage of carrying amount of our commercial nonperforming loans outstanding. Per Common Share: Earnings Per Share, Basic [Abstract] Operating Activities [Axis] Operating Activities [Axis] Securities Available for Sale Derivative Instrument, Debt Securities, Available For Sale [Member] Derivative Instrument, Debt Securities, Available For Sale Pledged Status [Axis] Pledged Status [Axis] Gross Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Net income (loss) attributable to Key common shareholders (in usd per share) Earnings Per Share, Basic LIABILITIES MEASURED ON A RECURRING BASIS Liabilities, Fair Value Disclosure [Abstract] Schedule of Fair Value of Derivative Assets by Type Schedule of Derivative Assets at Fair Value [Table Text Block] Cash dividends declared on preferred stock (in usd per share) Preferred Stock, Dividends Per Share, Declared Loan Portfolio Loans And Loans Held For Sale [Text Block] Discloses loans receivable and loans receivable held for sale. 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 speed 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 usd per share) Income (loss) from discontinued operations, net of taxes - assuming dilution (in usd 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 Gross Unrealized Gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain Time deposits, fair value Deposits, Fair Value Disclosure Measurement Input Type [Domain] Measurement Input Type [Domain] Equity Investments Indirect, NAV Equity Investments Indirect, NAV [Member] Equity Investments Indirect, NAV [Member] 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] 660 to 749 FICO Score, 660 to 749 [Member] FICO Score, 660 to 749 [Member] Writeoff, total Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Computer processing Communications and Information Technology Other Unconsolidated Variable Interest Entities Other Unconsolidated Variable Interest Entities [Member] Other Unconsolidated Variable Interest Entities Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Schedule of Accounts, Notes, Loans and Financing Receivable [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 short-term investments, excluding acquisitions 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] 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] 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] 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 AOCI, 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 Schedule of Credit Derivatives [Table] Credit Derivative [Table] Income (loss) from continuing operations before income taxes (TE) Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest and Tax Equivalents Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest and Tax Equivalents Net decrease (increase) in other investments Payments to Acquire Other Investments Treasury Stock, at Cost Treasury Stock, Common [Member] Current Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year Pay vs Performance Disclosure [Line Items] 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] Consumer Bank Community Banking [Member] Community banking. Preferred stock, liquidation preference per depositary share (in usd per share) Preferred Stock, Liquidation Preference Per Share LIABILITIES Liabilities [Abstract] Other direct noninterest expense Depreciation, Depletion and Amortization, Nonproduction Recognized on hedged items Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Schedule of Variable Interest Entities [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 Two years prior Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Writeoff, prior Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff Total commercial real estate loans Commercial Real Estate Loans [Member] Total commercial real estate loans. Comprehensive income (loss) attributable to Key Comprehensive Income (Loss), Net of Tax, Attributable to Parent Measurement Input Type [Axis] Measurement Input Type [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Name Measure Name Due in one year or less Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Equity Investments, Direct Equity Investments Direct [Member] Equity Investments Direct [Member] Net increase (decrease) in deposits Increase (Decrease) in Deposits Proceeds from prepayments and maturities of securities available for sale Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale Class of Stock [Line Items] Class of Stock [Line Items] Support and overhead Noninterest and Other Expense Noninterest and Other Expense Commitments Contingencies And Guarantees [Table] Commitments Contingencies And Guarantees [Table] Commitments Contingencies And Guarantees [Table] Deposits Average Deposits Average deposits. Income Tax Contingency [Table] Income Tax Contingency [Table] Long-term debt Long-term debt, carrying amount Total long-term debt Long-Term Debt Legal Entity [Axis] Legal Entity [Axis] Total assets VIE, assets that can only be used to settle obligations Total Assets Assets Cards and payments income Cards And Payments Income Cards And Payments Income Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Credit Derivatives Contract Type [Axis] Credit Derivatives Contract Type [Axis] Amount of offset in 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 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] OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Net derivatives 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] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Credit Score, FICO [Axis] Credit Score, FICO [Axis] Held-to-maturity securities fair value Fair Value Total Debt Securities, Held-to-Maturity, Fair Value Cash dividends declared on common shares (in usd per share) Common Stock, Dividends, Per Share, Declared Other investments Other Investments Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Bank notes and other short-term borrowings Short-Term Bank Loans and Notes Payable Due after five through ten years Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Level 2 Fair Value, Inputs, Level 2 [Member] Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Asset Pledged as Collateral Asset Pledged as Collateral [Member] Residential Mortgage Residential Mortgage [Member] Schedule of Sales-type Lease, Lease Income Sales-type Lease, Lease Income [Table Text Block] PEO PEO [Member] Effect on fair value from 10% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Default Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Default Rate Schedule of Securities by Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Effect on Fair Value of a 10% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial 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 Net change in: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Time deposits, carrying amount Time Deposits EARNINGS PER COMMON SHARE Earnings Per Common Share [Abstract] Earnings per common share. Retained Earnings Retained Earnings [Member] Fair value of collateral Valuation, Fair Value Of Underlying Collateral [Member] Valuation, Fair Value Of Underlying Collateral [Member] CASH AND DUE FROM BANKS AT BEGINNING OF PERIOD CASH AND DUE FROM BANKS AT END OF PERIOD Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Total derivative assets Derivative assets Derivative Asset Fair value, 12 months or longer Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Dividends paid per depositary share (in usd per share) Preferred Stock, Dividends, Per Share, Cash Paid Sale of Stock [Domain] Sale of Stock [Domain] Interest expense — Long-term debt Interest Expense [Member] Nonrecurring Fair Value, Nonrecurring [Member] Loans, net of unearned income (residential) Loans Held-For-Investment, Fair Value Disclosure Loans Held-For-Investment, Fair Value Disclosure Other intangible assets Intangible Assets, Net (Excluding Goodwill) Financing Receivable, Troubled Debt Restructuring [Table] Financing Receivable, Modified [Table] Other income Noninterest Income, Other Credit related to reserves on lending-related commitments Provision (credit) for losses on lending-related commitments Off-Balance-Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) Product and Service [Domain] Product and Service [Domain] SECURITIES AVAILABLE FOR SALE Securities available for sale: Debt Securities, Available-for-Sale [Abstract] Other noninterest income Other Noninterest Income [Member] Other Noninterest Income [Member] Securities pledged to secure securities sold under repurchase agreements Debt Securities, Available For Sale And Held To Maturity, Pledged Debt Securities, Available For Sale And Held To Maturity, Pledged Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Total liabilities on a recurring basis at fair value Liabilities measured at fair value on non recurring basis Liabilities, Fair Value Disclosure Notional Amount Derivative, Notional Amount Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Series H Preferred Stock Series H Preferred Stock [Member] Revolving Loans Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Revolving OREO and other Level 3 assets Other Real Estate City Area Code City Area Code Schedule of Financing Receivable, Allowance for Credit Loss Financing Receivable, Allowance for Credit Loss [Table Text Block] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] INVESTING ACTIVITIES Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Fair Value Hedging Fair Value Hedging [Member] Services charges on deposit accounts Service Charges On Deposit Accounts [Member] Service Charges On Deposit Accounts [Member] Schedule of Servicing Assets at Fair Value [Table] Servicing Asset at Fair Value, Activity [Table] Principal Investments Principal Investments [Member] Principal investments. Cash Flow Hedging Cash Flow Hedging [Member] Goodwill Goodwill Total sales-type and direct financing lease income Sales-type and Direct Financing Leases, Interest Income Default rate assumption Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Default Rate Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Default Rate Other long-term debt Other Long-Term Debt, Noncurrent Additional disclosures relative to cash flows: Supplemental Cash Flow Information [Abstract] Mortgage servicing assets excluded from OREO Mortgage Servicing Asset, Excluded From Other Real Estate Mortgage Servicing Asset, Excluded From Other Real Estate Other Performance Measure, Amount Other Performance Measure, Amount U.S. Treasury, agencies and corporations US Treasury and Government [Member] Loans Receivables [Abstract] Loans Receivables [Abstract] Loans Receivables [Abstract] Schedule of Direct Financing Lease, Lease Income Direct Financing Lease, Lease Income [Table Text Block] Derivative Instrument [Axis] Derivative Instrument [Axis] Total assets Average Assets Average total assets. Total commercial real estate loans Commercial Real Estate Portfolio Segment [Member] Leases Lessee, Finance Leases [Text Block] Entity [Domain] Entity [Domain] NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Loans Insured or Guaranteed by Government Authorities [Axis] Loans Insured or Guaranteed by Government Authorities [Axis] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Servicing Assets at Fair Value [Line Items] Servicing Assets at Fair Value [Line Items] Pretax gains related to the sale of mortgage loans Pretax Gains Related To The Sale of Mortgage Loans Pretax Gains Related To The Sale of Mortgage Loans Effective tax rate (as a percent) Effective Income Tax Rate Reconciliation, Percent 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 Default Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 20 Percent Adverse Change in Default Rate Equity Method Investment, Nonconsolidated Investee [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] Carrying Amount Reported Value Measurement [Member] Criticized (Accruing) Criticized Accruing [Member] Criticized Accruing [Member] Weighted-average remaining term for outstanding commercial mortgage loans (in years) Weighted Average Remaining Term For Outstanding Commercial Mortgage Loans Weighted-average remaining term for outstanding commercial mortgage loans. 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Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Series F Preferred Stock Series F Preferred Stock [Member] Government Guaranteed Loans Government Guaranteed Loans [Member] Government Guaranteed Loans [Member] Credit Derivatives Contract Type [Domain] Credit Derivatives Contract Type [Domain] Balance at beginning of period Balance at end of period Reserve for potential losses Off-Balance-Sheet, Credit Loss, Liability Federal funds purchased and securities sold under repurchase agreements Federal Funds Purchased and Securities Sold under Agreements to Repurchase ASSETS Assets [Abstract] Total provision, including discontinued operations Financing Receivable, Credit Loss, Expense (Reversal), Including Discontinued Operations Financing Receivable, Credit Loss, Expense (Reversal), Including Discontinued Operations Underlying Security Market Price Change Underlying Security Market Price Change, Percent Debt Instrument [Axis] Debt Instrument [Axis] Interest-bearing deposits Interest-Bearing Deposit Liabilities, Domestic Fair Value Measurements Fair Value Disclosures [Text Block] EQUITY Equity, Attributable to Parent [Abstract] Net increase (decrease) in short-term borrowings Proceeds from Short-Term Debt Schedule of Pre-Tax Net Gains (Losses) on Derivatives Not Designated as Hedging Instruments Pre Tax Net Gains Losses On Derivatives Not Designated As Hedging Instruments [Table Text Block] Pre tax net gains losses on derivatives not designated as hedging instruments. Schedule of Modified Financing Receivables Financing Receivable, Modified [Table Text Block] Senior Notes Due 2027-2039 Senior Notes Due 2027-2039 [Member] Senior Notes Due 2027-2039 Net gains (losses) on fair value hedging relationships Effect of Fair Value Hedges on Results of Operations [Abstract] Common Share repurchases Amount repurchased during period Treasury Stock, Value, Acquired, Cost Method Stated rate Debt Instrument, Interest Rate, Stated Percentage Originated Mortgage Servicing Rights Originated Mortgage Servicing Rights [Member] Originated Mortgage Servicing Rights 30-59 Days Past Due Financial Asset, 30 to 59 Days Past Due [Member] Schedule of Credit Risk Contingent Feature Credit Risk Contingent Feature [Table Text Block] Credit risk contingent feature. Remaining actual life of standby letters of credit (in years) Remaining Actual Life Letters Of Credit Remaining actual life letters of credit. Derivative Liabilities, net Derivative Liability, Not Subject to Master Netting Arrangement Due after five through ten years Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 5 through 10 Contingent Liabilities and Guarantees Commitments Contingencies and Guarantees [Text Block] Derivative assets Derivative Assets Derivative Asset, Subject to Master Netting Arrangement, before Offset Commitments outstanding to lend additional funds Financing Receivable, Modified, Commitment to Lend Depreciation, amortization, and accretion, net Depreciation, Amortization and Accretion, Net Held-to-maturity securities Interest Income, Debt Securities, Held-to-Maturity Entity Registrant Name Entity Registrant Name Loss expected to be reclassified Cash Flow Hedge Gain (Loss) to be Reclassified within 12 Months Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Number Of Reportable Segments Not Disclosed Flag Number Of Reportable Segments Not Disclosed Flag Number Of Reportable Segments Not Disclosed Flag Total assets on a recurring basis at fair value Assets, Fair Value Disclosure Provision for credit losses Provision for credit losses Provision for Loan, Lease, and Other Losses Total Past Due and Non-performing Loans Financial Asset, Past Due [Member] Other equity investments Equity Securities without Readily Determinable Fair Value, Amount Real estate — residential mortgage Real Estate Residential Mortgage [Member] Real estate - residential mortgage. Cash collateral netted against derivative assets Plus(Less): Related collateral Cash Collateral Netted Against Derivative Assets Cash collateral netted against derivative assets. Fair value, less than 12 months Debt Securities, Held-to-Maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value Restatement Determination Date: Restatement Determination Date [Axis] Interest income on deferred fees and costs Sales-Type And Direct Financing Lease, Interest Income, Deferred Fees And Costs Sales-Type And Direct Financing Lease, Interest Income, Deferred Fees And Costs Common Shares reissued (returned) for stock options and other employee benefit plans Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Interest income related to accretion of unguaranteed residual asset Sales-type Lease, Interest Income, Unguaranteed Residual Asset Name Trading Arrangement, Individual Name Underlying Asset Class [Domain] Underlying Asset Class [Domain] Cash dividends declared Dividends, Cash [Abstract] Maximum potential amount of undiscounted future payments possibly required as percentage of principal balance of loans outstanding (as a percent) Guarantor Obligations, Maximum Exposure, Undiscounted as Percentage of Total Loans Outstanding Guarantor Obligations, Maximum Exposure, Undiscounted as Percentage of Total Loans Outstanding Financial receivable, modifications, subsequent default, recorded investment Financing Receivable, Modified, Subsequent Default Loans held for sale Loans held for sale (residential) Loan, Held-for-Sale, Fair Value Disclosure High Risk Level, High [Member] Contractual fee income from servicing commercial mortgage loans Fees And Commissions Mortgage Banking And Servicing Before Amortization Fees and commissions, mortgage banking and servicing before amortization. Schedule of Loans by Category Loans By Category [Table Text Block] Loans by category. Net pension and postretirement benefit costs, tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Preferred Stock Preferred Stock [Member] Investment banking and debt placement fees Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions AVERAGE BALANCES Average Balances [Abstract] Average balances. Name Awards Close in Time to MNPI Disclosures, Individual Name Due after one through five years Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year One through Five Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Credit Loss [Abstract] Credit Loss [Abstract] Total other investments Other investments Alternative Investment Interest income on lease receivable Sales-type Lease, Interest Income, Lease Receivable Impairment loss Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount Net unrealized gains (losses) on securities available for sale, tax OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Segments [Domain] Segments [Domain] Income Statement Location [Axis] Statement of Income Location, Balance [Axis] Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Service charges on deposit accounts Service Charges On Deposit Accounts Service Charges On Deposit Accounts Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Written options Written Put Options, Guarantees [Member] Written Put Options, Guarantees Amount of offset in excess of securities collateral posted Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Securities Collateral Posted Derivative Instrument, Subject To Master Netting Arrangement, Collateral, Offset, Excess Securities Collateral Posted Balance Sheet Location [Domain] Statement of Financial Position Location, Balance [Domain] Percentage of loans held for sale and other nonperforming assets (as a percent) Percentage Of Loans Held For Sale And Other Nonperforming Assets Percentage of loans held for sale and other nonperforming assets. Unrealized gains (losses) on securities available for sale AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] INTEREST EXPENSE Interest Expense, Operating and Nonoperating [Abstract] Increase (decrease) in ALLL Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) Senior Notes Senior Notes [Member] Purchases of securities available for sale Payments to Acquire Debt Securities, Available-for-Sale Preferred stock Preferred Stock, Value, Issued States and political subdivisions US States and Political Subdivisions Debt Securities [Member] Securities Available for Sale, Fair Value Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] One year prior Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year Held-to-Maturity Securities, Fair Value Debt Securities, Held-to-Maturity, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Servicing Asset at Amortized Cost, Balance [Roll Forward] Servicing Asset at Amortized Cost, Balance [Roll Forward] Subordinated notes Subordinated Debt [Member] Financial Asset, Period Past Due [Axis] Financial Asset, Aging [Axis] Financial Asset, Aging [Axis] All Executive Categories All Executive Categories [Member] Common Shares, $1 par value; authorized 2,100,000,000 shares; issued 1,256,702,081 shares Common Stock, Value, Issued Short-term investments Short-Term Investments Recognized on derivatives designated as hedging instruments Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments Operating Activities [Domain] Operating Activities [Domain] Trading account assets Interest Income, Debt Securities, Trading, Operating Liquidation preference Preferred Stock, Liquidation Preference, Value Key Corp Key Corp [Member] Keycorp. Writeoff, current period Writeoff, current year Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff Measured at NAV Fair Value Measured at Net Asset Value Per Share [Member] Business Combination [Axis] Business Combination [Axis] Weighted average life of written put options (in years) Weighted Average Life Of Written Put Options Weighted average life of written put options. Interest income – loans Interest Income [Member] Government-guaranteed And Private Education Lending Business Government-guaranteed And Private Education Lending Business [Member] Government-guaranteed And Private Education Lending Business PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Due after ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 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] Loan assumption rate Interest Rate Used To Account For Mortgage Loan At Fair Value Upon Assumption Interest rate used to account for mortgage loan at fair value upon assumption. 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 Gross realized losses Debt Securities, Available-for-Sale, Realized Loss All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Name Forgone Recovery, Individual Name Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Nonperforming loans on nonaccrual status with no allowance Financing Receivable, Nonaccrual, No Allowance Corporate services income Banking Services Income Banking services income. Effect on fair value from 10% adverse change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Escrow Earn Rate Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of 10 Percent Adverse Change in Escrow Earn Rate Securities Available for Sale, Amortized Cost Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract] Writeoff, four year period Writeoff, four year Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff Schedule of Fair Values, Volume of Activity and Gain (Loss) Information Related to Derivative Instruments Schedule of Derivative Instruments [Table Text Block] Commitments Contingencies And Guarantees [Line Items] Commitments Contingencies And Guarantees [Line Items] Commitments Contingencies And Guarantees [Line Items] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Corporate services income Corporate Services [Member] Corporate Services [Member] Weighted average servicing fee rate Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Servicing Fee Rate Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Servicing Fee Rate Gross Unrealized Losses Debt Securities, Held-to-Maturity, Unrealized Loss Position, Accumulated Loss Schedule of Pre-Tax Net Gains (Losses) on Fair Value Hedges Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Total commercial loans Commercial Portfolio Segment [Member] Other operating activities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Net pension and postretirement benefit costs, net of income taxes of $(1) and $(21) 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 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. Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Short-term investments Interest Income, Operating Title of 12(b) Security Title of 12(b) Security Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Equipment Equipment Expense Income (loss) from continuing operations attributable to Key common shareholders (in usd per share) Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in usd 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] Writeoff, two year period Writeoff, two year 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 Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Common Share repurchases (in shares) Shares repurchased during period (in shares) Treasury Stock, Shares, Acquired 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 Award Timing Disclosures [Line Items] 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] 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] Loan Restructuring Modification [Domain] Loan Restructuring Modification [Domain] Net loans Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss NET INCOME (LOSS) Net income (loss) Net Income (Loss) Attributable to Parent 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 $29 and $(62) Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), after Adjustments and Tax, Parent Operating lease income related to lease payments Operating Lease, Lease Income, Lease Payments 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 Adoption Date Trading Arrangement Adoption Date Contract assets Contract with Customer, Asset, after Allowance for Credit Loss Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Retained earnings Retained Earnings (Accumulated Deficit) Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] LIHTC LIHTC investments LIHTC [Member] LIHTC Residual cash flows discount rate 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] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Credit Derivatives [Line Items] Credit Derivatives [Line Items] Statement [Table] Statement [Table] 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 and TE adjustments Income Tax Expense (Benefit) and Taxable Equivalent Adjustments Income Tax Expense (Benefit) and Taxable Equivalent Adjustments Basis of Presentation and Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Trading account assets Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI All Adjustments to Compensation All Adjustments to Compensation [Member] Interest Rate Reduction Contractual Interest Rate Reduction [Member] Amendment Flag Amendment Flag Debt securities, available for sale, accrued interest Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss Transfers and Servicing [Abstract] Treasury stock, at cost (169,409,323 and 154,301,387 shares) Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Less: Allowance for loan and lease losses Beginning balance Ending balance Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest 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). Weighted-average Common Shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Investment banking and debt placement fees Investment Banking and Debt Placement Fees [Member] Investment Banking and Debt Placement Fees 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] Segment Reporting [Abstract] Segment Reporting [Abstract] Ownership interest per depositary share ratio Entity Listing, Depository Receipt Ratio Operating lease expense Operating Lease, Expense 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. 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. 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] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Consolidated Entities [Axis] Consolidated Entities [Axis] Common shares, par value (in usd per share) Common Stock, Par or Stated Value Per Share Loans included in divestiture Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Leases Lessor, Direct Financing Leases [Text Block] Cash dividends paid Payments of Dividends Combined federal and state statutory tax rate (as a percent) Effective Income Tax Rate Reconciliation Federal And State Effective income tax rate reconciliation federal and state. Net occupancy Occupancy, Net Insider Trading Arrangements [Line Items] 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. Other operating leasing gains (losses) Operating Lease, Other Operating Leasing Gains (Losses) Operating Lease, Other Operating Leasing Gains (Losses) Amortized Cost Basis (as a percent) Financing Receivable, Excluding Accrued Interest, Modified in Period, to Total Financing Receivables, Percentage Total residential loans Residential Loans [Member] Residential Loans Series G Preferred Stock Series G Preferred Stock [Member] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Financial Instrument Performance Status [Domain] Financial Instrument Performance Status [Domain] Income (loss) from discontinued operations Income (loss) from discontinued operations, net of taxes 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] 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: $8,742 and $8,313) Held to maturity securities Amortized Cost Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Collateral posted Collateral Already Posted, Aggregate Fair Value