31 CFR § 1010.430 - Nature of records and retention period.
(a) Wherever it is required that there be retained either the original or a copy or reproduction of a check, draft, monetary instrument, investment security, or other similar instrument, there shall be retained a copy of both front and back of each such instrument or document, except that no copy need be retained of the back of any instrument or document which is entirely blank or which contains only standardized printed information, a copy of which is on file.
(b) Records required by this chapter to be retained by financial institutions may be those made in the ordinary course of business by a financial institution. If no record is made in the ordinary course of business of any transaction with respect to which records are required to be retained by this chapter, then such a record shall be prepared in writing by the financial institution.
(c) The rules and regulations issued by the Internal Revenue Service under 26 U.S.C. 6109 determine what constitutes a taxpayer identification number and whose number shall be obtained in the case of an account maintained by one or more persons.
(d) All records that are required to be retained by this chapter shall be retained for a period of five years. Records or reports required to be kept pursuant to an order issued under § 1010.370 of this chapter shall be retained for the period of time specified in such order, not to exceed five years. All such records shall be filed or stored in such a way as to be accessible within a reasonable period of time, taking into consideration the nature of the record, and the amount of time expired since the record was made.