Unmanageable and uninvestible. That is how investors have long considered Citigroup. For over a decade the bank, which was once the largest and most valuable in America, has been a basket case. It trades at half the value it did in 2006, making it the only big American bank to fetch a valuation lower than its peak before the global financial crisis. Pick any measure and Citi is invariably dead last compared with its rivals. The firm has more staff than Bank of America, yet makes only a third of the profit.