Exelon Corporation is an electricity generating and distributing company headquartered in the Chase Tower in the Chicago Loop area of Chicago. It was created in October, 2000 by the merger of PECO Energy Company and Unicom, of Philadelphia and Chicago respectively. Unicom owned Commonwealth Edison. Exelon has 5.4 million electricity customers and serves 485,000 natural gas customers in the Philadelphia suburbs. In October, 2009 Exelon had full or majority ownership of 17 nuclear reactors in 10 nuclear power plants.