The commission, for the purpose of ascertaining just and reasonable rates and charges of public utilities, or for any other purpose authorized by law, shall investigate and determine the value of the property of every public utility, except railroads and motor carriers, used and useful for the service and convenience of the public, excluding therefrom the value of any franchise or right to own, operate, or enjoy the same in excess of the amount, exclusive of any tax or annual charge, actually paid to any political subdivision of the state as a consideration for the grant of the franchise or right, and exclusive of any value of the right by reason of a monopoly or merger. The commission shall prescribe the details of the inventory of the property of each public utility to be valued.