It is the intent of the legislature by the adoption of this act, insofar as possible to make the provisions of the Idaho act identical to the provisions of the Federal Internal Revenue Code relating to the measurement of taxable income, to the end that the taxable income reported each taxable year by a taxpayer to the internal revenue service shall be the identical sum reported to this state, subject only to modifications contained in the Idaho law; to achieve this result by the application of the various provisions of the Federal Internal Revenue Code relating to the definition of income, exceptions therefrom, deductions (personal and otherwise), accounting methods, taxation of trusts, estates, partnerships and corporations, basis and other pertinent provisions to gross income as defined therein, resulting in an amount called "taxable income" in the Internal Revenue Code, and then to impose the provisions of this act thereon to derive a sum called "Idaho taxable income"; to impose a tax on residents of this state measured by Idaho taxable income wherever derived and on the Idaho taxable income of nonresidents which is the result of activity within or derived from sources within this state. All of the foregoing is subject to modifications in Idaho law including, without limitation, modifications applicable to unitary groups of corporations, which include corporations incorporated outside the United States.