Greg Fleming's decision to step down as president and chief operating officer of Merrill Lynch leaves Thomas Montag, the head of the bank's global markets business, as the sole remaining survivor of a trio of top lieutenants appointed by chief executive John Thain less than three months ago.

On Monday, Bob McCann, US-based head of global wealth management and head of the retail brokerage abruptly resigned. McCann, along with Fleming and Montag, was handed a senior job in the combined business in October and Ken Lewis, chairman and chief executive of Bank of America, had described the wealth management business as the best in the world when the merger was announced in September.