A Michigan subsidiary of St. Louis-based Ascension Health is planning to buy U.S. Health and Life Insurance Co. for $50 million. That's according to documents filed with the Michigan Department of Financial and Insurance Services, Crain's Detroit Business reports. Ascension Health would acquire the insurance company through a newly formed subsidiary, Ascension Care Management LLC, according to the publication. U.S. Health and Life, which targets employers with fewer than 100 workers, has received…