EXHIBIT 23(a) Consent of Independent Auditors We consent to the incorporation by reference in the registration statement (No. 333-04297) on Form S-3 of our report on the consolidated financial statements of Comerica Incorporated and subsidiaries dated January 16, 2003, incorporated by reference in the Annual Report on Form 10-K for the year ended December 31, 2002 filed with the Securities and Exchange Commission. /S/ ERNST & YOUNG LLP April 30, 2003 Detroit, Michigan