Businessweek

Ameren Corporation operates as a public utility holding company. The company’s subsidiaries operate rate-regulated electric generation, transmission and distribution businesses, rate-regulated natural gas transmission and distribution businesses, and merchant electric generation businesses in Missouri and Illinois. Subsidiaries Union Electric Company, or Ameren Missouri, operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 127,000 customers. Ameren Illinois Company, or Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business 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. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 806,000 customers. Ameren Energy Resources Company, LLC (AER) consists of non-rate-regulated operations, including Ameren Energy Generating Company (Genco), AmerenEnergy Resources Generating Company (AERG), Ameren Energy Marketing Company (Marketing Company) and, through Genco, an 80% ownership interest in Electric Energy, Inc. (EEI) that operates merchant electric generation energy centers and Federal Energy Regulatory Commission (FERC)-regulated transmission facilities in Illinois. History Ameren Corporation was founded in 1881.