Citigroup (C -0.30%) is one of the best-known banks in the United States and probably the world. But it doesn't have the best history when it comes to dealing with adversity, given its less-than-impressive performance during the Great Recession.Even though it is a much different company today than it was back then, investors can probably do better. Here's why and how.What does Citigroup do?Citigroup is a bank, providing basic financial services to consumers and businesses. This is the core of its business. ...