NEW YORK - Brian Williams, who remade his career as an MSNBC host after losing his job as NBC "Nightly News" anchor for making false claims about a wartime story, is leaving the network after 28 years.Williams said in a note to colleagues that "following much reflection," he had decided to exit when his contract ends in December."This is the end of a chapter and the beginning of another," Williams wrote. "There are many things I want to do, and I'll pop up again somewhere."Willliams, 62, said he will take a few months off to spend time with his family.FILE - Brian Williams attends the 2011 Museum of the Moving Image Gala.