May 13 (UPI) -- UnitedHealth Group announced Tuesday CEO Andrew Witty will step down, citing "personal reasons." Witty will leave the role of CEO and be replaced by Stephen J. Hemsley, effective immediately. "Leading the people of UnitedHealth Group has been a tremendous honor as they work every day to improve the health system and they will continue to inspire me," Witty said in a statement without providing further details on his decision to step away from the role. Witty will continue to