The  Treasury could cut its stake in bailed-out insurer American International Group Inc (AIG.N) by a fifth through a large stock offering in the first half of 2011, sources familiar with the matter said. AIG and the Treasury would both sell stock in the offering, which could total more than $10 billion, according to the sources. That would place it among the largest U.S. stock offerings in history. The sources are anonymous because these discussions are not public.