After losing nearly $15 billion in just six months, America's biggest bank laid out its plan for a comeback. New Citigroup CEO Vikram Pandit unveiled his strategy for reviving the bank. His plan: shed $400 billion in assets such as real estate, leveraged loans, and complex debt investments. ---restructure to yield $15 billion in benefits -- grow revenues by up to 10 percent annually. Gone is the idea of Citigroup being a one-stop shop for all things financial. Some investors called it a first good step, but wondered if Pandit can pull it off. Citigroup has suffered more than $45 billion in writedowns and credit losses due to the housing slump and bad mortgage loans. Guillermo Kopp is a former Citi executive who now works at Tower Group. "There are other institutions that are a little bit further ahead. So the challenge is can Vikrim execute fast enough, while still healing from the financial surgery and overtake some of their competitors?" Citigroup said it would bring back...