Mich. Comp. Laws § 487.3509

Sec. 509. Except where required or permitted under the federal reserve act, chapter 6, 38 Stat. 251, or the federal home loan bank act, chapter 522, 47 Stat. 725, a savings bank shall not deposit an amount in excess of 10% of the capital and surplus of a stock savings bank, or 10% of the total capital of a mutual savings bank, with any other savings bank, state chartered bank, association, or national bank. A savings bank may deposit an amount not to exceed 15% of the capital and surplus of a stock savings bank, or 15% of the total capital of a mutual savings bank in any legal depository in a reserve city designated by the commissioner.