Jan 4 - Fitch Ratings has assigned a 'BBB-' rating to The Allstate Corporation's (Allstate) $500 million subordinated debentures. Allstate issued $500 million of fixed-to-floating rate subordinated debentures with an initial coupon of 5.10% and a maturity of 2053. After January 2023, the fixed coupon changes to a floating rate of three-month LIBOR plus 3.165%. Interest on the notes is cumulatively deferrable for up to five years. Additionally, the notes are callable by Allstate with various res