CHATTANOOGA, Tenn. (AP) — BlueCross BlueShield of Tennessee has proposed raising premiums next year by an average of more than 36 percent after losing $141 million during its first year of offering individual health plans through the federal Affordable Care Act.The state's biggest health insurer said it initially underestimated the number and cost of the medical claims filed by new enrollees, the Times Free-Press reports.BlueCross Vice President Roy Vaughn said the insurer's mission was to serve the entire state as affordably as possible under the Affordable Care Act."It was a new market, and as we filed our initial rates for 2014 we had no data on the population that we would cover.