Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

Accounting Guidance Adopted in 2020

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2016-13, Measurement of Credit Losses on Financial Instruments ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments— Credit Losses ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments— Credit Losses ASU 2019-05, Financial Instruments— Credit Losses: Targeted Transition Relief ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments—Credit Losses ASU 2020-02, Financial Instruments—Credit Losses (Topic 326)— Amendments to SEC Paragraphs	January 1, 2020	The ASUs amend ASC Topic 326, Financial Instruments-Credit Losses, and significantly change how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The standard replaces today’s “incurred loss” approach with an “expected loss” model for instruments such as loans and held-to-maturity securities that are measured at amortized cost. The standard requires credit losses relating to available-for-sale debt securities to be recorded through an allowance rather than a reduction of the carrying amount. It also changes the accounting for purchased credit-impaired debt securities and loans. The ASUs retain many of the current disclosure requirements in current GAAP and expand certain disclosure requirements. The new guidance also allows optional relief for certain instruments measured at amortized cost with an option to irrevocably elect the fair value option in ASC Topic 825, Financial Instruments.	On January 1, 2020, we adopted ASC 326, Financial Instruments-Credit Losses, using the modified retrospective method. This new guidance affects the accounting for our loans, debt securities held to maturity and available for sale, and liabilities for credit losses on unfunded lending related commitments as well as purchased financial assets with a more-than insignificant amount of credit deterioration since origination. Our cross-functional implementation team, including finance, credit, and modeling, has completed the development and testing of loss forecasting models, including establishment of macroeconomic forecasting methodologies and approaches to meet the requirements of the new guidance. We completed parallel runs through the third and fourth quarters of 2019. We utilized a two-year reasonable and supportable forecast period for all portfolio segments and reverted to our historical loss experience outside of the forecast period over 1 year, leveraging historical macroeconomic variables. Based on our expectations of macroeconomic forecasts and our loans and net investment in leases as of January 1, 2020, we expect the allowance for loan and lease losses to increase by approximately 20% to 25% as compared to our current reserve levels as a result of the adoption of this guidance. The estimated allowance for loan and lease losses on longer duration consumer loans and lines of credit is expected to more than triple to cover the full remaining expected life of loans and commitments. The estimated overall increase is offset by an expected decrease in the allowance for loan and lease losses for our shorter duration commercial loans and leases. We do not expect to record an allowance for credit losses on available-for-sale or held-to-maturity debt securities as a result of the adoption of this guidance. The allowance for credit losses to be recorded at the January 1, 2020 transition date may differ from our estimate due to finalization of certain accounting, reporting, and governance processes.
ASU 2017-04, Simplifying the Test for Goodwill Impairment	January 1, 2020	The ASU amends ASC Topic 350, Intangibles - Goodwill and Other and eliminates the second step of the test for goodwill impairment. Under the new guidance, entities will compare the fair value of a reporting unit with its carrying amount. If the carrying amount exceeds the reporting unit’s fair value, the entity is required to recognize an impairment charge for this amount. The new method applies to all reporting units and the performance of a qualitative assessment is still allowable. The guidance should be implemented using a prospective approach.	We will monitor for impairment indicators and conduct our annual goodwill test as of October 1, 2020. The adoption of this accounting guidance is not expected to have a material effect on our financial condition or results of operations.

Accounting Guidance Adopted in 2019

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2016-02, Leases (Topic 842) ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient ASU 2018-10, Codification Improvements to Topic 842 ASU 2018-11, Leases (Topic 842): Targeted Improvements ASU 2018-20, Leases (Topic 842): Narrow Scope Improvements for Lessors ASU 2019-01, Codification Improvements to Topic 842	January 1, 2019	The ASUs create and amend ASC Topic 842, Leases, and supersede Topic 840, Leases. The new guidance requires that a lessee recognize assets and liabilities for leases with lease terms of more than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. Leveraged leases that commenced before the effective date of the new guidance are grandfathered. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, both types of leases are required to be recognized on the balance sheet. ASC 842 requires enhanced disclosures to better understand the amount, timing, and uncertainty of cash flows arising from leases. Qualitative and quantitative disclosures are required to provide additional information about the amounts recorded in the financial statements. Although substantially unchanged, certain amendments provide clarifications related to lessor accounting. The guidance should be implemented using a modified retrospective approach. However, entities may choose to measure and present the changes at the beginning of the earliest period presented or to reflect the changes as of the adoption date.	Key adopted this guidance on January 1, 2019, using the package of practical expedients, which allowed Key to maintain historic lease identification and classification, and permitted Key not to reassess initial direct costs under the new guidance. Key also elected the practical expedient on not separating lease components from nonlease components for all of its leases. Adoption resulted in an increase in right-of-use assets and associated lease liabilities arising from operating leases in which Key is the lessee of approximately $710 million on our Consolidated Balance Sheets at January 1, 2019. Right of use assets, lease liabilities, and other changes as a result of adoption are not reflected in comparable periods presented prior to that date. The adoption of this guidance did not have a material impact on the recognition of operating lease expense in our Consolidated Statements of Income. The amount of the right-of-use assets and associated lease liabilities recorded at adoption was based on the present value of unpaid future minimum lease payments. These payments were discounted using Key’s incremental borrowing rate, consistent with what Key would pay to borrow on a collateralized basis over a term similar to each lease. For more information, please see Note 10 (“Leases”).
ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities	January 1, 2019	The ASU amends ASC Topic 310-20, Receivables - Nonrefundable Fees and Other Costs, and shortens the amortization period to the earliest call date for certain callable debt securities held at a premium. Securities held at a discount will continue to be amortized to maturity. The guidance should be implemented on a modified retrospective basis using a cumulative-effect adjustment.	The adoption of this guidance did not have a material effect on our financial condition or results of operations.
ASU 2018-07, Stock Compensation - Improvements to Nonemployee Share-Based Payment Accounting	January 1, 2019	The ASU amends ASC Topic 718, Stock Compensation, and simplifies the accounting for share based payments granted to nonemployees for goods and services. The guidance should be implemented on a modified retrospective basis using a cumulative-effect adjustment.	The adoption of this guidance did not affect our financial condition or results of operations.
ASU 2018-13, Fair Value Measurement: Disclosure Framework	September 30, 2018 (removed disclosures only); January 1, 2019, remaining requirements An entity is permitted to early adopt any removed or modified disclosures upon issuance of this ASU and delay adoption of the additional disclosures until their effective date.	The ASU amends disclosure requirements related to fair value measurements. Specifically, entities are no longer required to disclose transfers between Level 1 and Level 2 of the fair value hierarchy, or qualitatively disclose the valuation process for Level 3 fair value measurements. The updated guidance requires disclosure of the changes in unrealized gains and losses for the period included in Other Comprehensive Income for recurring Level 3 fair value measurements. Entities also will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. The additional provisions of the guidance should be adopted prospectively, while the eliminated requirements should be adopted retrospectively.	Key removed the disclosures no longer required by the guidance as of September 30, 2018, and early adopted the additional provisions of the standard in the first quarter of 2019. The adoption of this standard did not result in significant changes to Key’s disclosures, and there was no effect to our financial condition or results of operations.
ASU 2018-14, Changes to the Disclosure Requirements for Defined Benefit Plans	December 31, 2019 Early adoption	The ASU amends the disclosure requirements for sponsors of defined benefit plans. Entities are required to provide new disclosures, including the weighted-average interest crediting rate for cash balance plans and explanations for the significant gains and losses related to changes in the benefit obligation for the period. Certain existing disclosure requirements are eliminated. The guidance should be adopted using a retrospective approach.	The adoption of this accounting guidance did not result in significant changes to our disclosures, and there was no effect on our financial condition or results of operations. Please see Note 18 (“Employee Benefits”) for updated disclosures.

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract	January 1, 2019 Early adoption	The ASU amends ASC Topic 350-40 to align the accounting for costs incurred in a cloud computing arrangement with the guidance on developing internal use software. Specifically, if a cloud computing arrangement is deemed to be a service contract, certain implementation costs are eligible for capitalization. The new guidance prescribes the balance sheet and income statement presentation and cash flow classification for the capitalized costs and related amortization expense. It also requires additional quantitative and qualitative disclosures. The guidance may be adopted prospectively or retrospectively.	Key early adopted this guidance effective January 1, 2019, on a prospective basis. The adoption of this guidance did not have a material effect on our financial condition or results of operations.
ASU 2019-04, Codification Improvements to Topic 815, Derivatives and Hedging (ASU Topic #3), and Topic 825, Financial Instruments (ASU Topic #4)	May 1, 2019 Early adoption upon issuance	The ASU provides technical corrections to previously adopted ASUs 2016-01 and 2017-12 and clarifies issues related to partial-term fair value hedges, fair value hedge basis adjustments, and how to measure changes in fair value of a hedged item. It also clarifies certain issues related to equity securities and the measurement alternative. Amendments related to ASU 2016-01 should be adopted using a modified retrospective approach, except for those related to equity securities without readily determinable fair values for which the measurement alternative is elected, which should be applied prospectively. We elected to apply amendments related to ASU 2017-12 on a prospective basis.	Key early adopted this guidance effective May 1, 2019. The adoption of this accounting guidance did not effect our financial condition or results of operations.