Mich. Comp. Laws § 830.422

Sec. 12. Bonds issued by the building authority under this act are securities in which banks, bankers, savings banks, trust companies, savings and loan associations, investment companies, and other persons carrying on a banking business, insurance companies, insurance associations, and other persons carrying on an insurance business, and administrators, executors, guardians, trustees, and other fiduciaries may properly and legally invest funds belonging to them or within their control.