ComEd CEO Joseph Dominguez will give up that job and becomes CEO of the power-plant side of Exelon, effective immediately, Exelon announced this morning. That company will be dubbed Constellation, the current name of Exelon's retail power and natural supply business, which will be part of Dominguez's domain. Calvin Butler, 52, who currently runs Exelon's regulated utilities as a group, will take over as interim CEO of ComEd. Rounding out the executive appointments, Exelon Chief Financial Officer Joseph Nigro will continue in that role for the new Exelon.