Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2024

Accounting Policies [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

Accounting Guidance Adopted in 2024

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2022-03, Fair Value Measurement - Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions (Topic 820)	January 1, 2024	The amendments clarify that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and is not considered in measuring fair value. Entities cannot, as a separate unit of account, recognize and measure a contractual sale restriction. The amendments require disclosures for equity securities subject to contractual restrictions including; the fair value of equity securities subject to contractual sale restrictions reflected in the balance sheet, the nature and remaining duration of the restriction(s) and the circumstances that could cause a lapse in the restriction(s). The guidance should be applied prospectively with any adjustments from the adoption of the amendments recognized in earnings and disclosed on the date of adoption.	The guidance did not have a material impact on Key’s financial condition or results of operations.
ASU 2023-07 Segment Reporting (Topic 280)	January 1, 2024	This guidance requires certain segment disclosures in annual and interim periods. It also clarifies that companies may report on additional measures if the chief operating decision maker uses more than one measure of a segment’s profit or loss in assessing segment performance and deciding how to allocate resources. The guidance should be applied on a retrospective basis.	This guidance did not have a material impact on Key’s financial condition or results of operations. Key updated its segment disclosures in Note. 25, Business Segment Reporting, to reflect this new guidance.

Accounting Guidance Adopted in 2025

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2023-09 Income Taxes (Topic 740)	Annual periods beginning January 1, 2025 Early adoption is permitted.	This guidance requires certain tax disclosures related to rate reconciliation and income taxes paid. The guidance should be applied on a prospective or retrospective basis.	The guidance is not expected to have a material impact on Key’s disclosures.