Does the employer by law have to provide written notification of termination and if so, how far in advance?

A friend of mine had this question:

I was called at work in a large corporation in mid-September by HR and told orally that my last day of work would be 10/30 and I would get an email with the details of the severance the following day.  I never received anything, in writing or otherwise, until a FedEx package with the terms of the severance arrived at my house on 10/30, terminating me (and my health insurance) that day.

Does the employer by law have to provide written notification of termination and if so, how far in advance?  (The company’s handbook states either party can end employment at will.)