Pros
Decent Salaries, great bonuses, great benefits, insane 401k matching, and generally fun coworkers. Fidelity tries to figure out what makes their employees happy - for example they recently started helping with student loans which was incredible. Certain teams have great dynamics and click really well with each other. There's a ton of diversity, so you get interesting perspectives from everyone.
Cons
They tend to promote people based on who has the loudest mouth. They also have a streak of hiring incompetent people and then moving them around instead of firing them. There are politics abound in most of the upper management and they try to obfuscate everything from lower employees. It is difficult to move around in Fidelity. I tried several moves, but kept getting blocked so I ended up leaving.