Friday December 6, 9:55 pm ET IRVING, Texas (Reuters) - Exxon Mobil Corp., the world's biggest publicly traded oil company, said on Friday a federal court in Alaska has decided it should pay $4 billion in punitive damages for the Exxon Valdez oil spill. Exxon Mobil, which argues that it should pay no more than $40 million for the 1989 tanker accident, said it planned to appeal the order. The decision was handed down by the federal court in Anchorage and reduced to $4 billion from $5 billion the amount of punitive damages awarded last year in connection with...