Andrew Witty, who largely led the U.S. healthcare giant from the U.K., made big bets on Medicare enrollees that backfired.

Andrew Witty is stepping down from his position as UnitedHealth's CEO for personal reasons, insurer says in surprise announcement.

UnitedHealth (UNH, Financials) shares gained 1% Monday after newly reinstated CEO Steve Hemsley apologized for the company's ...