Pub. Util. Code, § 792

The commission may establish a system of accounts to be kept by the public utilities subject to its jurisdiction, or classify such public utilities and establish a system of accounts for each class, and may prescribe the manner in which such accounts shall be kept. It may also prescribe the forms of accounts, records, and memoranda to be kept by such public utilities, including the accounts, records, and memoranda of the movement of traffic as well as the receipts and expenditures of moneys, and any other forms, records, and memoranda which in the judgment of the commission may be necessary to carry out any of the provisions of this part.