Michigan Compiled Laws, Chapter 500. Insurance Code of 1956 § 500.2812

(a) A provision substantially to the effect that the insurers executing the policy shall be severally liable for the full amount of any loss or damage, according to the terms of the policy, or for specified percentages or amounts thereof, aggregating the full amount of the insurance under the policy.

(b) A provision substantially to the effect that service of process, or of any notice or proof of loss required by the policy, upon any of the insurers executing the policy, shall be considered service upon all the insurers.