AM Best has downgraded the Long-Term Issuer Credit Ratings (Long-Term ICR) to "a-" (Excellent) from "a" (Excellent) and the Long and Short-Term Issue Credit Ratings (Long-Term IR; Short-Term IR) of UnitedHealth Group Incorporated (UnitedHealth Group) (Minnetonka, MN) [NYSE: UNH]. Concurrently AM Best has downgraded the Financial Strength Rating (FSR) to A (Excellent) from A+ (Superior) and the Long-Term ICRs to "a+" (Excellent) from "aa-" (Superior) of the health and dental insurance subsidiaries of UnitedHealth Group, collectively referred to as UnitedHealthcare. The outlook of these Credit Ratings (ratings) has been revised to stable from negative. (See link below for a detailed listing of the companies and ratings.) Concurrently, AM Best has affirmed the FSR of A (Excellent) and the Long-Term ICR of "a" (Excellent) of Centurion Casualty Company (Centurion Casualty) (Omaha, NE). The outlook of these ratings is stable.