Pros
Most of the organizations in Fannie Mae are full of senior leadership that encourages a culture of "you scratch-my-back-I'll scratch-yours". To enable this, they surround themselves with people who are "Yes Men". Most of the promotions are based on this dynamics of favoritism culture. It is more evident in the IT/Technology groups. Fannie Mae has some very bright people, but they stick around because either they have developed inertia or they are not employable outside. Most of leadership in IT/Technology is non-technical (including tons of managers and directors) who don't have a depth/breadth of technology comparable to a fresh CS graduate from a decent university. But they are in the top paying jobs because of their ability to "network".
Cons
Excellent benefits, decent work-life balance (even though it is deteriorating fast), okay pay structure.