Pros
Ameren includes Dental, standard Health, and Vision insurance as their employee health benefits. They also offer special savings accounts such as HSAs (Health Savings Accounts which are exempt on taxes for your health expenses). They also offer a 401k from the get-go and a company pension after being vested in the company for a number of years. Pair this with the reputation of the company and the general willingness to try and constantly improve and make both the company and the business better it is a great place to work. I have talked with many managers and supervisors across the company through email and everyone works very harmoniously and patiently with each other, for the most part.
Cons
There are some individuals, as I am sure there are everywhere that do not get properly disciplined for their work ethic or behavior. These always seem to be HR nightmares or from supervisors/managers not wanting to have to deal with it. Most promotions across Ameren are horizontal over periods of a year. If you want rapid raises you need to hop up to either higher technical jobs or management.