Commonwealth Edison (ComEd) faces the not-so-common task of powering up Chicago. ComEd, a subsidiary of utility holding company Exelon, distributes electricity to 3.8 million homes and businesses in Chicago and surrounding areas of Northern Illinois, representing 70% of population of the the state. The utility owns manages more than 90,000 circuit miles of transmission and distribution lines; it receives most of its power supply from sister company Exelon Generation. ComEd works with regional operator PJM Interconnection, which manages wholesale activities on the utility's transmission grid.