If corporate: a week's pay/year worked, some allowance for medical expenses, paid out vacation at 40%, and maybe a couple extra weeks of pay. You will also get information regarding the very expensive COBRA insurance, but the marketplace is probably cheaper at this point in the year. Good luck negotiating. If you don't accept it, then you probably just don't get a severance.
They will also shut down your access to your computer almost immediately, so make sure any personal information and files are cleared. They track things you send through your computer, so they will know if you have transferred any company documents, and will contact you when they find out.