Pros
Especially for people in the earlier stages of their careers, Northern Trust serves as a great training ground. I learned to run meetings, influence groups and stake holders, practice lots of public speaking, and generally become an all around more professional person. I also learned how to play office politics well--this may not be a particularly noble skill, but it is a valuable one in the realities of many workplaces.
Cons
Compensation is less than competitive, especially compared to other investment management firms. Politics and bureaucracy are all around stifling. There's also a good amount of talking behind people's back and general back stabbing. Senior leadership is wanting on many, many levels. One of their main job duties seems to be regularly re-organizing and re-shuffling the different units (at least on the investment side) so that they can send company-wide announcements on the changes. At least that keeps them busy so that the minions can get actual work accomplished.