OLDWICK, N.J.--( BUSINESS WIRE )-- A.M. Best Co. has affirmed the financial strength rating (FSR) of A+ (Superior) and issuer credit ratings (ICR) of "aa-" of Berkley Insurance Company (BIC) (Wilmington, DE) and 24 of its reinsured subsidiaries and affiliates, collectively referred to as W. R. Berkley Insurance Group.