Bank of America ( BAC) cleared the buyback of up to 200 million additional shares over the next 12 to 18 months.The Charlotte, N.C., bank said its board authorized it to spend $14 billion on buybacks. The board last approved an authorization of 200 million shares in April 2006. As of today, there are about 63 million shares remaining in that authorization. At year-end, Bank of America had 4 billion common shares outstanding. Shares fell 9 cents to $53.23.