Not to mention, murder is a state crime and lack of funding sometimes means the release of a murderer well before their sentence is served. That doesn't happen as much in the federal system. Skilling will probably serve at least 15 years before any chance of parole.
According to the legal talking heads on our local newscasts, there is no parole in federal prison. He will have to serve all of it, except any small breaks he earns for good behavior.