The first solid estimate of the economic harm caused by the Butte and Valley fires has arrived, and it’s a staggering number: nearly $2 billion in combined damages. The report by insurance company Aon Benfield confirms state officials’ fears that the twin wildfires, which transfixed much of Northern California during a two-week stretch in September, were among the costliest in the state’s history. The fires burned thousands of homes and other buildings, and left six people dead.