In 2004, Ameren acquired the third partner from the 1952 Midwest Power Pool system, Illinois Power Company, from Dynegy Inc. 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 reorganized as a holding company, Illinova Corporation, 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 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 Ameren's acquisition of Illinois Power, that subsidiary began doing business as AmerenIP. The IP acquisition made Ameren the major investor-owned power company in downstate Illinois.