Pros
Aon is willing to give you a chance even if you are not from the industry. The people are generally friendly and it is more laidback compared to others who have more aggressive targets and competitive environment. The companies differ greatly though so it depends very much which company, department, manager, and country! Aon Benfield has the intellectuals as they are very much into data and analytics so it is a great place to learn. You can grow fast as they do put you in front of client early. Aon Hewitt has a plethora of innovative new products and best benefits but it can be too casual - maybe it's the consulting nature so the staff tend to be more flippant. Aon Risk Solutions is the core business and its size contributes to the multiple lines of policies and expertise. You can learn from the seasoned staff or drown in its volume and administrative tasks. Top management ie. those in UK and USA speak the values and culture talk. Access to senior management is rather flat so you can grow fast if you put in extra effort to increase visibility.
Cons
Middle management doesn't implement the strategies nor do they ingrain the values and culture. They are busy building their own mini kingdoms; this is particularly true in local offices where the countries are far from HQ. Perception is that those who put in the effort and perform get "rewarded" with more work and higher expectations. They need to support slackers who get promoted due to their "boss management" skills and desperation level of that department to retain employees so they don't look bad. Internal promotions are not the culture so you need to really look for opportunities yourself. Your manager may just direct you to the company website! No active mentoring and annual review is the only time you get performance discussions. People managers are not really trained to be a leader but they get promoted due to years in company, relationship with the bosses, or desperation of the department to retain the staff to avoid looking bad in staff retention!