Ameren is a utility holding company whose primary assets are its equity interests in its subsidiaries. It operates through four segments: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. The company is engaged in the rate-regulated electric generation, transmission, and distribution as well as rate-regulated natural gas distribution and transmission activities. It primarily generates electricity through coal, nuclear, and natural gas, as well as renewable sources, such as hydroelectric, methane gas, and solar. Ameren Corporation was formed as a result of a merger between Union Electric Company and Central Illinois Public Service Company.