Ameren Corporation is a utility holding company. The Company's primary assets are its equity interests in its subsidiaries, including Ameren Missouri, Ameren Illinois, and Ameren Transmission Company of Illinois (ATXI). The Company's business segments include Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas and Ameren Transmission. The Ameren Missouri segment includes all 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 Ameren Transmission segment primarily consists of the aggregated electric transmission businesses of Ameren Illinois and ATXI.