220 ILCS 5/7-205
If any public utility is engaged in carrying on any business other than that of a public utility, which other business is not otherwise subject to the jurisdiction of the Commission, that public utility in respect of such other business shall be subject to inquiry, examination and inspection by the Commission in the same manner as the public utility business insofar as such inquiry, examination and inspection may be necessary to enforce any provision of this Act. The determination of the Commission that a necessity for any regulation of nonpublic business of a public utility exists shall be prima facie evidence of the fact in any action in a court of this State to enforce or set aside an order or ruling of the Commission.
Every public utility and affiliated interest thereof shall provide the Commission with access to books, records, accounts, documents and other data and information which the Commission finds necessary to effectively implement and effectuate the provisions of Section 7-204.
220 ILCS 5/7-205