Nothing surprising there. However this number shouldn't be disregarded at all. They have either lost this amount of money (showing signs of corruption) or they have been doing secret projects everywhere that nobody really knows anything about.
I don't think that most of the money was lost to corruption. It seems that most of it was spent on classified projects, all over the world. The United States have been doing all sort of dirty work around the world for the last 70 years or so. This includes bribing local dictators and politicians, and supporting terrorist organizations. All this require money.