Ameren is the holding company for the following:
The AmerenUE subsidiary owns Bagnell Dam on the Osage River, which forms the Lake of the Ozarks. AmerenUE is responsible for managing water levels on the lake according to federal regulations; if levels are not appropriate, the lake must be closed until Ameren can solve the problem.
In 1931, Union Electric Light and Power sought additional generating sources (interurbans being one need) and the company began buying power from the Keokuk, IA dam, 150 miles north of St. Louis. Union Electric later bought the dam, providing 134 megawatts of hydroelectricity carried over a longer distance than had ever been achieved before.
By the 1950s Union Electric owned gas operations in and around Alton, Illinois, and acquired other utilities to become the third largest distributor of natural gas in Missouri.
In 1952, Ameren's second major constituent, the Central Illinois Public Service Company, became a major pooled energy power distributor with its future Ameren mate, Union Electric Company. The arrangement formed the Midwest Power Pool system. The CIPS Meredosia, Illinois Power Station became a key contributor to the pool, which also included the later Ameren subsidiary Illinois Power Company.
In 1963 Union Electric completed construction of one of the largest pumped storage plants at that time, the then-350-megawatt Taum Sauk Plant, in Reynolds County, Missouri.
The merger was completed on December 31, 1997, when the two public companies became one, as Ameren Corporation, which then began to trade publicly on the New York Stock Exchange with the ticker symbol AEE.
The former CIPSCO Inc. utility, Central Illinois Public Services Company, is now a subsidiary of the Ameren Corporation holding company, known as AmerenCIPS.
Following the merger, Union Electric began doing business as AmerenUE. Today, with nine power plants AmerenUE serves 1.2 million power customers and 110,000 gas customers, primarily in Missouri, where more than half of its customers reside in the St. Louis metropolitan area. It also serves adjoining parts of Illinois, and formerly served Iowa as well through the mid-1990s.
In 2000, Ameren formed the holding company, AmerenEnergy Resources. It contained two further subsidiaries, AmerenEnergy Marketing, and AmerenEnergy Generating.
In 2003, Ameren acquired the Central Illinois Light Company. That utility's holding company, CILCORP, Inc., had traded on the NYSE with ticker symbol CER, and by the mid-1990s had become a member of the S&P Small Cap 600 index. CILCORP had been another pioneer utility in the region, which had paid a dividend since 1921. By 1996, it had grown to over US$150 million in assets, and carried US$330 million in long-term debt. Following the 2003 Ameren acquisition, that utility then became the subsidiary, AmerenCILCO.
In 2004, Ameren acquired (from Dynegy Inc.) its third partner from the 1952 Midwest Power Pool system, Illinois Power Company. That utility had traded publicly on the NYSE under the ticker symbol IPC through the 1980s, and paid dividends since 1947. As of the late 1980s, the company generated electricity and natural gas, almost entirely from coal plants, with less than 1% fueled from oil and gas. By then, with about $360 million in assets, it carried long-term debt of over US$2 billion. In 1991, Illinois Power became the subsidiary of holding company Illinova Corp., which traded on the NYSE with ticker symbol ILN. Illinova had grown to an S&P Midcap 400 stock by 1996, with over US$415 million in assets, and had brought the IP utility's debt down to US$1.8 billion by then. In a merger completed February 1, 2000, Illinova Corp. became a wholly-owned subsidiary of Dynegy Inc. in which Chevron Corporation also took a 28% stake. Dynegy in turn had been created in June 1998, from the merger of Chevron's natural gas and natural gas liquids businesses with Dynegy's predecessor, NGC Corp. (former ticker NGL). NGC had been an integrated natural gas services company around since 1994. Following the 2004 Ameren acquisition of the IP utility, that subsidiary became AmerenIP.
AmerenUE owns the Taum Sauk pumped storage plant, which failed on December 14, 2005, because Ameren pumped water over the upper reservoir wall. FERC fined Ameren $15 million. The State of Missouri has sued Ameren for actual and punitive damages, alleging Ameren recklessly operated the plant and put financial considerations from sale of power to other companies over safety, maintenance and engineering. The plant was operated by remote control with no one onsite during pumping operations. Missouri Attorney General Jay Nixon has been criticized by Republican officials and others for soliciting campaign contributions from Ameren during the Taum Sauk investigation. He has been cleared by a state ethics panel and returned the money.