Sullivan & Cromwell successfully stayed a federal court decision that threatened to erode the work product doctrine and attorney-client confidentiality in a widely followed appeal that will have a big impact on corporate internal investigations. The appeal stemmed from a securities class action filed against FirstEnergy Corp. in an Ohio federal court, which sought billions of dollars in damages. On a “mandamus” appeal—which is rarely granted—the U.S. Court of Appeals for the Sixth Circuit issued the August 7 stay.