Millennium Insurance was created in the aftermath of the Battle of Detroit. In the destruction that would end the City of Detroit itself, all the local insurance companies were insolvent trying to cover the insurmountable number of claims made by their clients.
Two generations of the de Raven family - Robert and Phillip - managed to orchestrate enough regulatory support and financial investors to buy out the remnants of those insolvent companies to create a new one... an insurance company for the "New Millennium" and for the new Millennium City.
Millennium Insurance offered whole coverage for all sorts of situations, including supervillain damage, monster attacks, and alien/extradimensional invasions.
Millennium Insurance has storefronts all through Millennium City.