Japan's Meiji Yasuda Life Insurance said Friday it has agreed to buy StanCorp Financial Group for $5 billion as it aims to expand its overseas business in the face of limited growth at home.Meiji Yasuda said in its statement that the purchase of the U.S. group, one of the biggest transactions ever by a Japanese life insurance company, is part of its bid to expand profits.StanCorp will become a wholly-owned subsidiary of the Japanese insurer early next year, after approval by shareholders of the U.S. group and by U.S. regulators.