Citibank announces shockingly large losses stemming from investments in subprime mortgages. That could completely wipe out fourth-quarter earnings for the largest bank in the country. It was the last straw for Citigroup Chairman and CEO Charles Prince. He resigned Sunday after an emergency meeting. That makes him the second Wall Street chief executive within a week to lose his job. Last week it was Stanley O'Neal, who was the CEO of Merrill Lynch, after losses of more than $8 billion. Neither executive had enough successes to make up for those losses. Citigroup's stock has fallen about 20 percent in the last month. Analysts and investors say Charles Prince failed in his strategy to remake Citigroup into a "universal bank" that pulls in revenue from all kinds of financial services.