The chiefs of Japan's top insurance companies are eager to keep pursuing mergers and acquisitions abroad because the domestic market is expected to shrink, interviews show.

In 2015, Nippon Life Insurance Co. bought smaller rival Mitsui Life Insurance Co. and National Australia Bank's insurance business, but still has ¥1 trillion ($8.3 billion) to spend on further acquisitions, according to President Yoshinobu Tsutsui.

He hinted that Nippon Life is seeking M&A deals in the United States, as that "is the largest market in the world."