Ameren Corporation (Ameren) is a utility holding company. The Company's principal subsidiaries are Union Electric Company (Ameren Missouri), Ameren Illinois Company (Ameren Illinois) and Ameren Energy Resources Company, LLC (AER). The Company operates in three segments: Ameren Missouri, Ameren Illinois, and Merchant Generation. Ameren Missouri operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri. Ameren Illinois operates a rate-regulated electric and natural gas transmission and distribution business in Illinois. In December 2013, Dynegy Inc announced that its subsidiary, Illinois Power Holdings (IPH) completed its acquisition of New Ameren Energy Resources (AER), an Ameren subsidiary.