(a) An insurer shall not have at any one time any single investment or combination of investments in or loans upon the security of the obligations, property, or securities of any one person aggregating in cost to the insurer in excess of the greater of 10 percent of such insurer's assets or the total of its capital and surplus, as shown in the latest annual report of the insurer filed pursuant to subsection (a) of Section 27-3-26 of the Alabama Insurance Code, less the minimum capital and surplus required of said insurer for authority to transact insurance by Sections 27-3-7 and 27-3-8 of the Alabama Insurance Code. The restriction of this subsection shall not apply to evidences of indebtedness issued, assumed, or guaranteed by the United States of America or any department, agency, or instrumentality thereof or by any state of the United States.