Prudential Financial Inc.’s Japan insurance head vowed to bolster governance after revelations that improper actions by more than 100 current and former staff cost customers about $20 million.The chief executive officer of the unit, Kan Mabara, “deeply” apologized for “multiple inappropriate cases,” at a news conference in Tokyo. Prudential Life Insurance Co. had said in a statement last week that employees had received ¥3.14 billion ($20 million) from customers through improper acts. It said last week that ...