Her untimely departure comes as ComEd and Exelon are entangled in a federal corruption probe of several current and former politicians in Illinois. The most recent of those centers on state Sen. Martin Sandoval, whose daughter Angie works for ComEd and was hired while Pramaggiore, 61, served as CEO.

A Sept. 23 federal search warrant identified, but did not name, four separate Exelon officials in a request for items “related to” them “and/or any issue supported by any of those businesses or individuals, including but not limited to rate increases.”

Exelon and ComEd disclosed Oct. 9 that they were a focus of the Sandoval probe and that Exelon had established a special committee made up of independent directors to oversee compliance with the federal investigation. Two days later, the search warrant was made public.

A short time before, on Oct. 4, ComEd disclosed in a Securities & Exchange Commission filing that Fidel Marquez, senior vice president at ComEd in charge of government affairs, had retired Oct. 2.

The terse wording in Exelon’s press release didn’t give a reason for Pramaggiore’s retirement. A spokesman declined to comment on whether it had anything to do with the probe.

Succeeding Pramaggiore, at least for now, is Calvin Butler Jr., who steps up from his current role as CEO of Exelon-owned Baltimore Gas & Electric. Butler, 49, moved to Baltimore from Chicago, where he had served years ago in various executive roles at ComEd. Butler’s position is interim, but ComEd CEO Joseph Dominguez, as well as other heads of Exelon’s various utilities, will report to him.

Pramaggiore’s elevation to CEO of all of Exelon’s utilities, announced last year, identified her as a potential successor to Exelon CEO Chris Crane. Until now, she had been perceived as a rising star at ComEd and Exelon ever since she joined ComEd in 1998. She was the first female CEO in ComEd’s 100-year-plus history when she succeeded Frank Clark in 2012.

Under her tenure, ComEd pushed major initiatives through Springfield, most notably the 2011 smart-grid law that authorized $2.6 billion in grid-modernization investments over a decade and permitted the utility to set its rates annually via a formula that gave regulators little latitude to change. Those delivery rates then jumped 37 percent from 2013 to 2019, padding ComEd’s profits and aiding its parent company Exelon at a time when power prices were falling and pressuring its nuclear plants financially.