CHICAGO--(BUSINESS WIRE)--Fitch Ratings has placed Sirius International Group, Ltd.'s (Sirius) Issuer Default Rating (IDR) of 'BBB+', senior debt rating of 'BBB', and operating subsidiaries' Insurer Financial Strength (IFS) ratings of 'A' on Rating Watch Evolving. Fitch also affirmed White Mountains Insurance Group, Ltd.'s (White Mountains) IDR at 'BBB+'. A full list of rating actions follows at the end of this release. KEY RATING DRIVERS Fitch's rating action follows the announcement today tha