Federal sentencing guidelines take into account many things. You get (bad) points (called levels) for how many people you harmed, dollar value of the harm, whether or not you used "sophisticated" means, etc, etc. These points are then converted to a sentence length according to this[1] chart. The main contributor in a case like this is going to be the dollar amount of the fraud (which is huge), as those points stack up quickly, capping out at 30 levels for a fraud of over $550M. So if as assume he gets the highest level, that's 30 levels on its own, which if you read the guideline chart linked means a recommended sentence of 8 years for a first time offender just from those levels alone. Add all the other levels in and you can get to 43 (life imprisonment for first time offenders) pretty quickly.
