The length of time an employer is required to keep various types of employment records varies with both the state and the type of record involved. For example, I-9 forms need to be kept till a year after termination or three years after hire, whichever is longer. On the other hand, payroll records need to be kept three or four years (I forget which) and there are some records that need to be kept as long as 30 years.
Company policy only applies once the legal requirements have been met. For example, if the law requires that a particular record be kept for seven years, company policy cannot decide to only keep them five. On the other hand, they can, if they so choose, opt to keep them for ten.
The regulatory agency for all records is not going to be the DOL. If you want to indicate what records you're concerned about, someone here may be able to direct you. But the regulatory agency for the specific record is going to have the answer for you; there's not going to be one single source that can tell you the length of time for ALL records, unless some employment attorney somewhere has put together a template or something on the subject.