Ameren Corporation (Ameren) is a utility holding company. The Company operates in two segments: Ameren Missouri and Ameren Illinois. The Company's subsidiaries include Ameren Missouri and Ameren Illinois. Ameren also has a subsidiary, ATXI that operates a FERC rate-regulated electric transmission business. Ameren Missouri operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas transmission and distribution business in Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. Ameren Illinois operates rate-regulated electric and natural gas transmission and distribution businesses in Illinois. Ameren Illinois supplies electric and natural gas utility service to portions of central and southern Illinois in an area of 40,000 square miles.