CHICAGO--(BUSINESS WIRE)--Fitch Ratings has assigned a senior unsecured debt rating of 'A-' to Marsh & McLennan Companies, Inc.'s (MMC) new issue of $600 million 3.75% senior notes due 2026. Fitch has also affirmed MMC's Long-term Issuer Default Rating (IDR) and existing senior unsecured debt ratings at 'A-' and short-term ratings at 'F2'. A full list of MMC's ratings follows at the end of this release. The Rating Outlook is Stable. KEY RATING DRIVERS Fitch expects MMC to use the net procee