Maurice R. Greenberg, the former chief executive of American International Group, reached an unexpected settlement ending a tumultuous, decade-long battle over civil accounting fraud charges first brought in 2005 by New York Attorney General Eliot Spitzer, the New York Times DealBook blog reported on Friday. Greenberg, 91, and his co-defendant, Howard Smith, AIG’s former chief financial officer, reached the agreement with the current New York attorney general, Eric T. Schneiderman, who announced it on Friday. In the settlement, the two men acknowledged that they had participated in and approved two transactions that inaccurately portrayed AIG’s financial results over four years. They agreed to give up more than $9.9 million that they received as performance bonuses from 2001 through 2004, with Greenberg paying most of that amount. But it is a fraction of the more than $50 million the state had sought.