"The Insurance Capital of the World" - you've heard the term if you've ever lived in Hartford. Many of the nation's insurance companies have at one point called the city home. The tradition started in 1810 with the founding the Hartford Fire Insurance Company (now the Hartford). The business's reach expanded greatly over time, as insurance became more popular. Aetna followed with a large local office in 1857. expanding several times over the years. Travelers followed shortly after. The last two left made their mark on the city by creating local historic landmarks.
So, how do you know if your ancestor was involved in the insurance industry? Check the census. Chances are this may be the only evidence of your ancestor's work. Aetna and others don't seem to have accessible archives.