NEW YORK ( TheStreet ) -- Standard & Poor's lowered its credit rating on American International Group 's ( AIG ) Chartis subsidiary on Monday, citing weaker-than-expected operating performance. But it also revised the outlook for AIG and all of its operating companies to stable from negative, believing the firm will become more competitive and build upon operating improvements since its bailout - particularly at its SunAmerica division. S&P downgraded Chartis' ratings one notch, to "A" from "A+." It kept the rest of AIG's ratings stable, including its overall "A-" rating and the "A+" rating on SunAmerica. Chartis, AIG's property & casualty division, reported a $4.1 billion charge last quarter to bolster reserves - a move some investors hadn't expected. In a conference call on Friday, CEO Robert Benmosche and other executives attempted to shore up confidence about Chartis' strength.