OLDWICK, N.J.--(BUSINESS WIRE)--A.M. Best has upgraded the financial strength rating to A (Excellent) from A- (Excellent) and the issuer credit rating to “a” from “a-” of The Mutual Risk Retention Group, Inc. (The Mutual) (headquartered in Walnut Creek, CA). The outlook for the ratings has been revised to stable from positive. The ratings of The Mutual reflect its excellent balance sheet strength, long-term underwriting and operating profitability and the advantages gained from its core special