Ameren Corp. operates as a public utility holding company that provides electric and natural gas services. It operates through the following business segments: Ameren Missouri and Ameren Illinois. The Ameren Missouri segment operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri. The Ameren Illinois segment operates a rate-regulated electric and natural gas transmission and distribution business in Illinois. The company was founded in 1997 and is headquartered in St. Louis, MO.