CHICAGO--(BUSINESS WIRE)--Fitch Ratings has affirmed the ratings of RenaissanceRe Holdings Ltd. (NYSE: RNR) and its subsidiaries, including the Issuer Default Rating (IDR) for RNR at 'A', and the Insurer Financial Strength (IFS) rating of Renaissance Reinsurance Ltd. at 'A+'. Fitch has also upgraded RNR's preference shares to 'BBB+' from 'BBB'. The Rating Outlook is Stable. A full list of ratings follows at the end of this release. KEY RATING DRIVERS The upgrade of the preference shares reflect