Correct answer for this question is: Five independent agencies—A.M. Best, Fitch, Kroll Bond Rating Agency (KBRA), Moody's and Standard & Poor's—rate the financial strength of insurance companies. Each has its own rating scale, its own rating standards, its own population of rated companies, and its own distribution of companies across its scale.
The title of my answer can be How to assess the financial strength of an insurance company