Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

Accounting Guidance Adopted in 2021

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2019-12, Simplifying the Accounting for Income Taxes	January 1, 2021	This ASU simplifies the accounting for income taxes by removing certain exceptions to the existing guidance, such as exceptions related to the incremental approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss, and the recognition of deferred tax liabilities when a foreign subsidiary becomes an equity method investment and when a foreign equity method investment becomes a subsidiary. Along with general improvements, it adds simplifications related to franchise taxes, the tax basis of goodwill, and the method for recognizing an enacted change in tax laws. The guidance also specifies that an entity is not required to allocate the consolidated amount of certain tax expense to a legal entity not subject to tax in its own separate financial statements. The guidance should be applied on either a retrospective, modified retrospective, or prospective basis depending on the amendment.	The adoption of this accounting guidance did not have a material effect on our financial condition or results of operations.
ASU 2020-01, Clarifying the Interactions between Topic 321,Investments —Equity Securities; Topic 323, Investments— Equity Method and Joint Ventures; and Topic 815, Derivatives and Hedging	January 1, 2021	This guidance clarifies that when applying the measurement alternative in Topic 321, companies should consider certain observable transactions that require the application or discontinuance of the equity method under Topic 323. It also clarifies that companies should not consider whether the underlying securities in certain forward contracts and purchased options would be accounted for under the equity method or fair value option when determining the method of accounting for those contracts. This guidance should be applied on prospective basis.	The adoption of this accounting guidance did not have a material effect on our financial condition or results of operations.
ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs	January 1, 2021	This ASU clarifies that at each reporting period an entity should reevaluate whether a callable debt security is within the scope of ASC 310, which says that to the extent the amortized cost basis of an individual callable debt security exceeds the amount repayable by the issuer at the earliest call date, the premium shall be amortized to the earliest call date, unless prepayment guidance is applied. This guidance should be applied on a prospective basis.	The adoption of this accounting guidance did not have a material effect on our financial condition or results of operations.
ASU 2021-01, Reference Rate Reform (Topic 848)	January 1, 2021	The ASU clarifies that certain optional expedients and exceptions related to contracts modified as a result of reference rate reform and hedge accounting apply to derivatives affected by the discounting transition, such as those that use an interest rate for margining, discounting, or contract price alignment. The guidance may be applied on a full retrospective basis as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020.   Alternatively, it may be applied on a prospective basis to new modifications from any date within an interim period that includes or is subsequent to the date of the issuance of a final Update, until the financial statements are available to be issued.	Key adopted this guidance on January 1, 2021, on a prospective basis and will assess the impact in conjunction with the reference rate transition. We have elected to apply certain optional expedients for contract modifications and hedging relationships to derivative instruments impacted by the market-wide discounting transition. These optional expedients remove the requirement to remeasure contract modifications or dedesignate hedging relationships due to reference rate reform. We plan to elect any optional expedients for contract modifications and hedging relationships to any other financial instruments falling under the scope of reference rate reform.
Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services— Investment Companies (Topic 946)	December 31, 2021	The FASB updated the SEC section of the Codification to reflect two releases issued in 2020 to improve disclosure rules related to depository lending and investment companies. Disclosure requirements have been updated to codify certain Guide 3 disclosure items and eliminate other Guide 3 disclosure items that overlap with Commission rules and U.S. GAAP. Further, codified disclosure requirements were moved to a new part of Regulation S-K.	The adoption of this accounting guidance did not materially impact Key’s financial statement disclosures. Updates to disclosures included the elimination of duplicative disclosures already required by the SEC and U.S. GAAP, as well as streamlining the presentation of prior period information in MD&A to align with periods presented in the financial statements. Additional disclosures regarding uninsured deposits amounts and loan categories required by Regulation S-K were also included.

Accounting Guidance Adopted in 2022

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40)	January 1, 2022 Early adoption is permitted.	The ASU simplifies the accounting for convertible debt instruments by eliminating the legacy accounting models for convertible instruments with beneficial conversion features or cash conversion features. The guidance also amends the guidance used to determine if a freestanding financial instrument or an embedded feature qualifies for a scope exception from derivative accounting. For freestanding financial instruments and embedded features that have all the characteristics of a derivative instrument and are potentially settled in an entity’s own stock, the guidance simplifies the settlement assessment that entities are required to perform. Also, the Update now requires the use of the if-converted method for all convertible instruments and includes the effect of potential share settlement in diluted EPS if the effect is more dilutive. The new guidance also makes clarifications to the EPS calculation. Further, the ASU expands disclosure requirements. The guidance should be applied on a modified retrospective or retrospective basis.	The adoption of this accounting guidance did not have a material effect on our financial condition or results of operations.