In ascertaining the reasonableness of a rate or charge to be made by a public utility, no charge for services rendered by a holding or affiliated company, or charge for material or commodity furnished or purchased from a holding or affiliated company, shall be given consideration in determining a reasonable rate or charge unless there be a showing made by the utility affected by the rate or charge as to the actual cost to the holding or affiliated company furnishing such service and material or commodity. Such showing shall consist of an itemized statement furnished by the utility setting out in detail the various items, cost for services rendered and material or commodity furnished by the holding or affiliated company.