S&P Global Ratings upgraded its ratings for First Horizon National Corp. and its unit, First Tennessee Bank NA, citing the company's improved asset quality and low likelihood of outsized charges related to its legacy mortgage business.

The rating agency raised the Memphis, Tenn.-based company's long-term issuer credit rating to BBB- from BB+ and the banking subsidiary's long- and short-term ratings to BBB/A-2 from BBB-/A-3.

The outlook on both long-term ratings is stable.

S&P credit analyst Shameer Bandeally said the stable outlook reflects the rating agency's view that the company's nonperforming assets will continue to decline and the legal and repurchase risks associated with the mortgage business have been "largely dealt with."

S&P Global Ratings and S&P Global Market Intelligence are owned by S&P Global Inc.