Pros
Outstanding benefis, plenty of room for advancement and pay-increases beyond the usual merit bump (just don't expect it to be dropped in lap, you need to express interest and show that you're serious), and many opportunities for job-specific training, mentoring/shadowing, and higher education. Very challenging projects wtih aggressive timelines that will expand your experience (and your resume) by leaps and bounds.
Cons
Departments are often short-staffed in relation to the workloads - A project that should have 10 team members may only have three or four. If you're not flexible and willing to balance multiple roles and pick up work that falls outside your 'comfort zone', this organization isn't for you. Do not expect to keep your head down, work a normal 9-to-5 and get ahead at this company. Those types of jobs are plentiful at BNYM, but you won't move up. The hard work pays off, but expect 10-12 hour days, off-hours conference calls (this is a global company with offices in practically every time zone), heavy travel, and plenty of 'working weekends'. You have to be vocal about what you want and what your career goals are, or management will assume you're comfortable with the status quo. Still plenty of politics due to the merger between Mellon and BofNY - enough that it can occasionally hinder progress. Learn to play nice in the sandbox and try to bridge the gaps between the legacy-company teams, and you'll be fine.