Dating back to 1879, Tokio Marine is Japan's oldest insurance company and was its top property and casualty insurer in terms of market share for many decades. After mergers of its smaller rivals in the past few years, the company is now roughly the same size in the domestic nonlife market as MS&AD and Sompo Holdings, but it remains the most valuable listed Japanese insurer in terms of market capitalization due to its larger overseas business portfolio. The majority of its overseas business is in the U.S., where it has purchased four specialty insurers since 2008: Philadelphia Consolidated, Delphi Financial, HCC, and PURE. It is a member of the Mitsubishi keiretsu group and holds minority stakes in a number of group companies that also rank among its shareholders.