 Moodys Investors Service Moodys upgraded the senior unsecured rating of CenterPoint Energy Resources Corp. CERC to A3 from Baa1 and affirmed its Prime-2 short-term rating for commercial paper. The upgrade reflects the reduction in CERCs business risk effected through the completed sale of its energy marketing business and an expected cash flow-to-debt ratio of around 20, said Robert Petrosino, Moodys Vice President -- Senior Analyst. 