Aug 16 (Reuters) - Insurance broker Willis Towers Watson said on Monday company insider Carl Hess would be its next CEO and president, weeks after the collapse of a planned $30 billion merger with rival Aon Plc.

Hess, who currently heads the firm's investment, risk and reinsurance segment, will take over the chief executive officer role on Jan. 1 after the retirement of John Haley.

Willis and London-based rival Aon called off their merger following an "impasse" with the U.S. Department of Justice. Had it been approved, the deal would have created the world's largest insurance broker.

Hess joined Willis in 1989. He will take on the president role immediately. (Reporting by Niket Nishant in Bengaluru; Editing by Maju Samuel)