Citi is the last global wholesale bank offering all products to its clients everywhere. It operates in 100 countries and boasts a payment system handling $3 trillion of transactions a day, which no other bank is ever likely to emulate. It has taken the axe to its global consumer business, but still operates in 24 countries. Under the leadership of Michael Corbat, Citi has closed the share price discount to book value. It must now prove that a global universal bank can avoid the pitfalls of scale and deliver sustainable returns. If it does, it will be the only one