Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

Accounting Guidance Adopted in 2017

Standard	Date of Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2016-09, Improvements to Employee Share-Based Payment Accounting	January 1, 2017	The ASU requires entities to recognize the income tax effects of share-based awards in the income statement when the awards vest or are settled (i.e. the additional paid-in capital pools will be eliminated). The guidance on employers’ accounting for an employee’s use of shares to satisfy the employer’s statutory income tax withholding obligation and for forfeitures is changing. The standard also provides an entity the option to make an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur.	During the year ended December 31, 2017, the application of this guidance resulted in recognition of $28 million in excess tax benefits within “income taxes” on our income statement. Adoption did not materially affect our Consolidated Statements of Cash Flows, nor did it affect retained earnings as of the beginning of the period of adoption. We elected to retain our existing accounting policy of estimating award forfeitures upon the award’s grant date.
ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220)	October 1, 2017	On December 22, 2017, the TCJ Act was signed into law. Under current U.S. GAAP, deferred tax assets and liabilities are to be adjusted for the effect of a change in tax laws or rates with the effect included in income from continuing operations in the reporting period that includes the enactment date. This accounting treatment resulted in the tax effect of items within accumulated other comprehensive income not reflecting the appropriate tax rate. This ASU allows stranded tax effects resulting from the TCJ Act to be reclassified from accumulated other comprehensive income to retained earnings.	We early adopted this guidance during the quarter ended December 31, 2017, resulting in a reclassification of $141 million from accumulated other comprehensive income to retained earnings to adjust the tax effect of items within accumulated other comprehensive income to reflect the newly enacted federal corporate income tax rate. Refer to Note 14, Income Taxes, for additional information.

Accounting Guidance Pending Adoption at December 31, 2017

Standard	Required Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ASU 2015-14, Deferral of Effective Date ASU 2016-08, Principal versus Agent Considerations ASU 2016-10, Identifying Performance Obligations and Licensing ASU 2016-11, Rescission of SEC Guidance because of Accounting Standard Updates 2014-09 and 2014-16 pursuant to Staff Announcements at the March 3, 2016 EITF Meeting ASU 2016-12, Narrow-scope Improvements and Practical Expedients ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers	January 1, 2018 Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2016	These ASUs supersede the revenue recognition guidance in ASC 605, Revenue Recognition, and most industry-specific guidance. The core principle of these ASUs is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. These ASUs can be implemented using a retrospective method, or a cumulative-effect approach to new contracts and existing contracts with performance obligations as of the effective date.	We have identified the revenue line items within the scope of the new guidance and have finalized our contract testing related to trust and investment services income, investment banking and debt placement fees, service charges on deposit accounts, and cards and payments income. The new guidance will change our presentation of certain underwriting and credit and debit card related costs. Underwriting costs will change from a net presentation to a gross expense. Certain credit and debit card related costs will change from a gross presentation to a reduction in revenue. Additionally, we will expand our qualitative and quantitative disclosures pursuant to the new requirements Key will adopt using a cumulative-effect approach. The adoption of this accounting guidance will not have a material effect on our financial condition or results of operations.

Standard	Required Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities	January 1, 2018 Early adoption is not permitted, except under certain circumstances	The ASU amends ASC Topic 825, Financial Instruments-Overall, and requires equity investments, except those accounted for under the equity method of accounting or consolidated, to be measured at fair value with changes recognized in net income. If there is no readily determinable fair value, the guidance allows entities the ability to measure investments at cost less impairment, whereby impairment is based on a qualitative assessment. The guidance eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost and changes the presentation of financial assets and financial liabilities on the balance sheet or in the footnotes. If an entity has elected the fair value option to measure liabilities, the new accounting guidance requires the portion of the change in the fair value of a liability resulting from credit risk to be presented in OCI. With the exception of disclosure requirements that will be adopted prospectively, the ASU must be adopted on a modified retrospective basis.	The adoption of this guidance will not have a material effect on our financial condition or results of operations.
ASU 2016-02, Leases (Topic 842)	January 1, 2019 Early adoption is permitted	The ASU creates ASC Topic 842, Leases, and supersedes Topic 840, Leases. The ASU 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, the ASU will require both types of leases to be recognized on the balance sheet. It also requires disclosures to better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. Upon transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach.	Key has formed a cross-functional team to oversee the implementation of this ASU. Implementation efforts are ongoing, including the review of our lease portfolios and related lease accounting policies, the review of our service contracts for embedded leases, and the deployment of a new lease software solution. Key’s adoption of this ASU will result in an increase in right-of-use assets and associated lease liabilities, arising from operating leases in which Key is the lessee, on our Consolidated Balance Sheet. The amount of the right-of-use assets and associated lease liabilities recorded upon adoption will be based primarily on the present value of unpaid future minimum lease payments, the amount of which will depend on the population of leases in effect at the date of adoption. Key’s minimum future rental payments under noncancelable operating leases would be measured and recognized when the new guidance is adopted (refer to Note 22 (“Commitments, Contingent Liabilities, and Guarantees”). While these leases represent a large majority of the leases that are within scope of the new leasing standard, we will continue to review service contracts up through the effective date and may identify additional leases embedded in those arrangements that will be within the scope of the new standard. In addition to final determination of the lease portfolio at the effective date, the initial measurement of the right-of-use asset and the corresponding liability will be affected by certain key assumptions such as expectations of renewals or extensions and the interest rate to be used to discount the future lease obligations. We do not expect the adoption of this guidance to have a material impact on our Consolidated Statements of Income.
ASU 2016-13 Measurement of Credit Losses on Financial Instruments	January 1, 2020 Early adoption is permitted as of January 1, 2019	The ASU amends ASC Topic 326, Financial Instruments-Credit Losses, and significantly changes 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 HTM securities that are measured at amortized cost. The standard requires credit losses relating to AFS 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 ASU retains many of the current disclosure requirements in current GAAP and expands certain disclosure requirements.	This new guidance will affect 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. Key has formed a cross-functional implementation working group comprised of teams throughout Key, including finance and credit. The implementation team has developed a high-level project plan, is identifying and researching key interpretive issues, and is in the process of developing models that meet the requirements of the new guidance. The implementation team is also in the process of assessing forecast accuracy and potential macroeconomic factors that will be used to determine the reasonable and supportable forecast period. Key expects that the new guidance will generally result in an increase in its allowance for credit losses, as it will cover credit losses over the full remaining expected life of loans and commitments and will consider future changes in macroeconomic conditions. Since the magnitude of the anticipated increase in the allowance for credit losses will be impacted by economic conditions and trends in the Company’s portfolio at the time of adoption, the quantitative impact cannot yet be reasonably estimated.

Standard	Required Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments.	January 1, 2018 Early adoption is permitted	The ASU amends ASC Topic 230, Statement of Cash Flows, and clarifies how cash receipts and cash payments in certain transactions should be presented and classified in the statement of cash flows. These specific transactions include, but are not limited to, debt prepayment or extinguishment costs, contingent considerations made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, and distributions from equity method investees. This guidance also clarifies that in instances of cash flows with multiple aspects that cannot be separately identified, classification should be based on the activity that is likely to be the predominant source of or use of cash flow. The guidance should be implemented using a retrospective approach.	The adoption of this accounting guidance will not have a material effect on the presentation of our Consolidated Statements of Cash Flows, as Key’s current policies are either already in-line with the clarifications in the updated guidance, or the related cash flows are not material.
ASU 2017-04, Simplifying the Test for Goodwill Impairment	January 1, 2020 Early adoption is permitted	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.	The adoption of this accounting guidance is not expected to have a material effect on our financial condition or results of operations.
ASU 2017-05, Other Income- Gains and Losses from the Derecognition of Nonfinancial Assets	January 1, 2018 Early adoption is permitted	The ASU amends ASC Topic 610-20, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets to clarify the scope of the Topic by clarifying the definition of the term "in substance nonfinancial asset" and also adding guidance for partial sales of nonfinancial assets. Under the new guidance, an entity will derecognize a nonfinancial asset when it does not have or ceases to have a controlling interest in the legal entity that holds the asset and when control of the asset has transferred in accordance with ASC 606. The ASU can be adopted on a retrospective or modified retrospective approach.	The adoption of this guidance will not have a material effect on our financial condition or results of operations.
ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost	January 1, 2018 Early adoption is permitted within the first interim period if the entity issues interim financial statements.	The ASU amends ASC Topic 715, Compensation - Retirement Benefits, and requires service costs to be included in the same line item as certain other compensation costs related to services rendered by employees. We record compensation costs under personnel expense on the income statement. Other elements of net benefit cost should be presented separately. The guidance should be implemented on a retrospective basis.	The adoption of this guidance will result in a reclassification of certain net benefit cost components from personnel expense to other expense on the income statement. There will be no material effect on our financial condition or results of operations.
ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities	January 1, 2019 Early adoption is permitted.	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 is not expected to have a material effect on our financial condition or results of operations.
ASU 2017-09, Scope of Modification Accounting	January 1, 2018 Early adoption is permitted, including interim periods.	The ASU amends ASC Topic 718, Compensation - Stock Compensation, and clarifies when changes to terms and conditions for share-based payment awards should be accounted for as modifications. Under the new guidance, entities should apply the modification guidance unless the fair value of the modified award is the same as the fair value of the original award immediately before modification, the vesting conditions of the modified award are the same as the vesting conditions of the original award immediately before modification, and the classification of the modified award (as equity or liability instrument) is the same as the classification of the original award immediately before modification. The guidance should be applied on a prospective basis.	The adoption of this guidance will not have a material effect on our financial condition or results of operations.

Standard	Required Adoption	Description	Effect on Financial Statements or Other Significant Matters
ASU 2017-01, Clarifying the Definition of a Business	January 1, 2018 Early application is allowed for certain transactions.	The ASU amends Topic 805, Business Combinations, and clarifies the definition of a business and removes the requirement for a market participant to consider whether it could replace missing elements in an integrated set of assets and activities. The guidance states that if substantially all of the fair value of the assets acquired or disposed of is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. The guidance should be implemented using a prospective approach.	The adoption of this guidance will not have a material effect on our financial condition or results of operations.
ASU 2017-12, Targeted Improvements to Accounting for Hedging Activities	January 1, 2019 Early adoption is permitted, including interim periods. Key anticipates early adopting this standard as of January 1, 2018.	The ASU amends ASC Topic 815, Derivatives and Hedging, to simplify the requirements for hedge accounting and facilitate financial reporting that more closely aligns with an entity’s risk management activities. Key amendments include: eliminating the requirement to separately measure and report hedge ineffectiveness, requiring changes in the value of the hedging instrument to be presented in the same income statement line as the earnings effect of the hedged item, and the ability to measure the hedged item based on the benchmark interest rate component of the total contractual coupon for fair value hedges. Additional disclosures are also required for reporting periods subsequent to the date of adoption. The guidance should be implemented on a modified retrospective basis to existing hedge relationships as of the adoption date.	We will adopt this ASU in the first quarter of 2018. Our financial statements for the quarter ended March 31, 2018, will include a cumulative-effect adjustment to opening retained earnings to reflect the application of the new guidance as of January 1, 2018. The primary impact to Key at adoption is the election to measure the change in fair value of the hedged item in fair value hedges on the basis of the benchmark interest rate component of contractual coupon cash flows. The cumulative-effect entry at adoption will reflect a cumulative basis adjustment for existing fair value hedges to be under the benchmark component approach. We expect adoption of this ASU to reduce hedge ineffectiveness going forward; however, we do not anticipate this guidance to have a material effect on our financial condition and results of operations.