Ameren Corporation operates as a public utility holding company in the United States. It operates in three segments: Ameren Missouri, Ameren Illinois, and Merchant Generation. The company engages in rate-regulated electric generation, transmission, and distribution businesses; and rate-regulated natural gas transmission and distribution businesses, as well as merchant electric generation businesses. It primarily generates electricity through coal, nuclear, natural gas, and hydroelectric sources. Ameren Corporation primarily serves residential, commercial, and industrial customers. The company was founded in 1881 and is headquartered in St. Louis, Missouri.