Basis of Presentation and Accounting Policies	6 Months Ended
Basis of Presentation and Accounting Policies	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation and Accounting Policies	BASIS OF PRESENTATION AND ACCOUNTING POLICIES Organization The accompanying unaudited consolidated financial statements were prepared in accordance with United States (U.S.) generally accepted accounting principles (GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, the statements do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation were included. The results of operations for the three and six months ended June 30, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. Certain items in prior periods were reclassified to conform to the current presentation. The accompanying unaudited financial statements should be read in conjunction with the consolidated financial statements and footnotes included in the Annual Report on Form 10-K of Comerica Incorporated and Subsidiaries (the Corporation) for the year ended December 31, 2023 (2023 Annual Report). Accounting Pronouncements Recently Adopted Effective January 1, 2024, the Corporation adopted the provisions of Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2023-02, "Investments-Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method (a consensus of the Emerging Issues Task Force)" (ASU 2023-02). ASU 2023-02 expanded the permitted use of the proportional amortization method, which was previously only available to low-income housing tax credit investments, to other tax equity investments if certain conditions are met. Under the proportional amortization method, the initial cost of an investment is amortized in proportion to the income tax benefits received and both the amortization of the investment and the income tax benefits received are recognized as a component of income tax expense. ASU 2023-02 was adopted on a modified retrospective basis of transition or, for certain changes, a prospective basis and resulted in a reduction to retained earnings as of January 1, 2024 of $4 million. Recently Issued Accounting Pronouncements In November 2023, the FASB issued ASU No. 2023-07 "Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures" (ASU 2023-07). The update requires enhanced disclosures about significant segment expenses, enhanced interim disclosure requirements, clarification for when multiple segment measures of profit or loss can be disclosed and other requirements intended to improve overall reportable segment disclosures in annual and interim periods. ASU 2023-07 is effective for the Corporation in the annual period beginning on January 1, 2024 and interim periods beginning on January 1, 2025 with retrospective application to all prior periods presented. Early adoption is permitted. The Corporation is evaluating the impact of ASU 2023-07 on its reportable segment disclosures. In December 2023, the FASB issued ASU No. 2023-09 "Income Taxes (Topic 740): Improvements to Income Tax Disclosures" (ASU 2023-09). ASU 2023-09 requires additional annual disclosures including further disaggregation of information in the rate reconciliation, additional information for reconciling items meeting a quantitative threshold, further disaggregation of income taxes paid and other required disclosures. ASU 2023-09 is effective for the Corporation in the annual period beginning on January 1, 2025 and applied on a prospective basis with both early adoption and retrospective application permitted. The Corporation is evaluating the impact of ASU 2023-09 on its income tax disclosures.