Pros
The large organization presents opportunities for advancement, and there are many training options available. The compensation is competitive, including a pension plan in addition to a 401k. Bonuses are also available, thought they are very dependent on overall company profits, and profits can be greatly affected by events outside the control of the company and its employees, such as natural disasters that require large cash payouts by the company. The working environments are generally good, with current equipment and tools, and offices well-maintained. The top management does a good job of communicating company goals and results, but upper management within each organization does not do as good a job.
Cons
There seems to be constant "right-sizing" that causes uncertainty by employees about the stability of their job. There are significant pressures to deliver within sometimes arbitrary target dates, and to work overtime to meet expectations. At the same time, the message from management is to support work/life balance. Each of the companies within the larger organization suffer cutbacks independently of other companies, so you may work in a company that is struggling and being part of a larger, succesful organization may not save your job. Within the IT organization, there seems to be a bit of age bias toward younger talent, so if you are over 50, opportunities are not as abundant.