By Karlee Weinmann (July 25, 2013, 11:47 AM EDT) -- A mammoth initial public offering worth as much as $40 billion could be on the way for Japan Post Holdings Co. Ltd., the conglomerate that runs 20,000 post offices as well as its home country's biggest financial services and insurance operations, Reuters reported Wednesday. The much-anticipated deal could come as soon as spring 2015, half a year ahead of a previously outlined schedule thanks to the group's thriving insurance branch. Feeding into that success, Japanese media have closely followed an agreement between Japan Post and American Family Life Insurance Co., the U.S. firm known as Aflac, to sell Aflac's cancer insurance offerings through its network of Japanese post offices. When it has discussed its public float in the past, Japan Post has has said it would help raise money for redevelopment in areas destroyed by the earthquake and tsunami that walloped the region in March 2011....