UnitedHealth Group on Tuesday said Chairman Stephen Hemsley will return to the helm of the health care conglomerate, succeeding CEO Andrew Witty.  Witty is stepping down for "personal reasons," effective immediately, UnitedHealth said. Hemsley served as chief executive from 2006 to 2017.The company didn't disclose other details about Witty's sudden departure, though Hemsley commended his "stewardship of UnitedHealth Group, especially during some of the most challenging times any company has ever faced." UNI ...