Ameren Corporation is a utility holding company. The Company's subsidiaries include Ameren Missouri, Ameren Illinois and Ameren Transmission Company (ATXI). It operates through four segments. The Ameren Missouri segment includes all of the operations of Ameren Missouri. The Ameren Illinois Electric Distribution segment consists of the electric distribution business of Ameren Illinois. The Ameren Illinois Natural Gas segment consists of the natural gas business of Ameren Illinois. The ATXI segment consists of the aggregated electric transmission businesses of Ameren Illinois and ATXI. Ameren Missouri operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Illinois operates rate-regulated electric distribution, electric transmission and natural gas distribution businesses in Illinois. ATXI operates a Federal Energy Regulatory Commission rate-regulated electric transmission business.